RKGSl  Es? 

CoIumMa  ®nttier^itp 

mtl)e€itpof3lmlork 

^cfjool  of  l^ental  anb  0xal  burger? 


LIBRARY  OF 

Dr.  carl  F.  W.  BODECKER 

1846-1912 

The  gift  of 

Dr.  Henry  and  Dr.  Charles  Bodecker 

1929 


Digitized  by  tine  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/americantextbookOOessi 


LIST  OF  CONTillBUTOilS. 


BURCHARD,  HENRY  H.,  M.D.,  D.  D.S. ; 
ESSIG,  CHARLES  J.,  M.  D.,  D.D.S.; 
EVANS,  W.  W.,  D.  D.S.; 
GODDARD,  C.  L.,  A.M.,  D.  D.  S."; 
MOLYNEAUX,  GRANT,  D.  D.S.; 
OTTOLENGUI,  RODRIGUES,  M.D.S.; 
TEES,  AMBLER,  Jr.,  D.D.S.  ; 
THOMPSON,  ALTON  HOWARD,  D.D.S. 


/^       / ^   /^    t>^^i^  ^— (_^^^ — y 


>-— <w.^ 


THE 


AMERICAN  TEXT-BOOK 


or 


PROSTHETIC  DENTISTRY. 


IN  CONTRIBUTIONS  BY  EMINENT  AUTHORITIES. 


EDITED  BY 

CHARLES  J.  ESSIG,  M.D,  D.D.S., 

Professor  of  Mechanical  Dentistry  and  Metallurgy,  Department  of  Dentistry, 
University  of  Pennsylvania,  Philadelphia. 


ILLUSTRATED    WITH    983    ENGRAVINGS. 


Messrs.  Lea  Brothers  &  Co.  in- 
tend this  book  to  be  sold  to  the  Public 
at  the  advertised  price,  and  supply  it 
to  the  Trade  on  terms  which  will  not 
allow  of  discount. 


PHILADELPHIA  AND  NEW  YORK. 

1896. 


LIST  OF  CONTRIBUTORS. 


BURCHARD,  HENRY   H.,  M.D.,  D.D.S.; 
ESSIG,  CHARLES  J.,  M.  D.,  D.D.S. ; 
EVANS,  W.  W.,  D.  D.S.; 
GODDARD,  C.  L.,  A.M.,  D.D.S.'; 
MOLYNEAUX,  GRANT,  D.D.S.; 
OTTOLENGUI,  RODRIGUES,  M.D.S.; 
TEES,  AMBLER,  Jr.,  D.D.S.; 
THOMPSON, 


fL^/^/ZX 


THE 


^U^-^'^-C^^!L-f^i^ 


AMERICAN  TEXT-BOOK 


PROSTHETIC  DENTISTRY. 


IN  CONTRIBUTIONS  BY  EMINENT  AUTHOBITIES. 


EDITED  BY 

CHAELES  J.  ESSIG,  M.D,  D.D.S., 

Pkofessok  of  Mechanical  Dentistry  and  Metallurgy,  Department  op  Dentistry, 
University  of  Pennsylvania,  Philadelphia. 


ILLUSTRATED    WITH    983    ENGRAVINGS. 


LEA   BROTHERS   &   CO., 

PHILADELPHIA  AND  NEW  YORK. 

1896. 


Entered  according  to  Act  of  Congress  in  the  year  1896,  by 

LEA.  BROTHERS   &   CO., 

in  the  Office  of  the  Librarian  of  Congress,  at  Washington.     All  rights  reserved. 


WESTCOTT    &.    THOMSON,  PRESS    OF 

ELECTROTYPERS,    PHILADA-  WILLIAM  J.    DORNAN,   PHILADA. 


WITH  THE  CONSENT  OF  THE 

SEVERAL   CONTRIBUTORS 
THIS   VOLUME  IS   INSCRIBED   AS  A   RECOGNITION 

OF 

PROFESSIONAL  EMINENCE  AND  PRIVATE  WORTH 

TO 

LOUIS   JACK,  D.D.S., 

BY   HIS   FRIEND   AND   FORMER  ASSOCIATE 

THE   EDITOR. 

September  12, 1896. 


PREFACE. 


If  the  Editor  interprets  correctly  the  prevailing  opinion  of  the  den- 
tal profession  as  reflected  in  the  utterances  of  many  teachers,  the  issue 
of  an  extended  and  strictly  modern  text-book  upon  the  Principles  and 
Practice  of  Prosthetic  Dentistry  will  answer  a  need  of  the  times. 
During  the  past  thirty  years  the  practice  of  prosthesis  has  undergone 
a  transformation  parallel  with  that  of  operative  dentistry  during  the 
same  period.  Plans,  operations,  and  methods  which,  despite  the  retro- 
spective asseverations  of  many,  were  but  crude  and  indefinite,  have 
received  a  development  which  has  widened  this  branch  of  dental  practice 
and  greatly  increased  its  utility. 

There  is  contained  in  the  body  of  the  present  volume  the  material 
which  a  consensus  of  opinion  declares  the  best  that  dental  prosthetic  art 
has  evolved.  It  is  designed  to  answer  the  purposes  of  a  text-book  for 
the  under-graduate  student,  a  clear  and  thorough  laboratory  manual, 
and  a  work  of  reference  for  the  dental  practitioner. 

In  conformity  with  these  plans,  the  central  object  is  the  exposition  of 
principles  and  the  teaching  of  their  practical  application.  No  eifort  has 
been  spared  by  Editor  and  collaborators  to  survey,  arrange,  and  classify 
the  mass  of  data  gleaned  from  the  literature  of  the  past  fifty  years  and 
from  the  practice  of  those  who  have  raised  prosthetic  dentistry  to  its 
present  plane. 

In  arranging  this  vast  accumulation  of  material  so  that  one  case 
might  be  correctly  placed  as  representative  of  a  class,  matters  which  are 
not  directly  pertinent  to  the  subject  of  laboratory  technology  are  delib- 
erately excluded  from  these  pages,  it  being  confidently  believed  that  a 
mastery  of  the  technique  and  materials  presented  will  give  the  student 
a  command  of  the  subject  throughout  its  many  ramifications.  The 
means  employed  to  this  end  are  lucidity  of  description  and  such 
a  wealth  of  illustration  as  to  render  the  text  as  clear  as  words  and 
pictures  can  make  it.  Particularly  in  the  matter  of  engravings  the 
publishers  have  been  more  than  liberal,  desiring  that  the  book  should, 
above  all,  fill  the  gap  complained  of  by  teachers — the  want  of  a  complete 
and  modern  text-book  from  which  obsolete  and  useless  material  should 
be  expunged. 


10  PREFACE. 

It  is  a  prominent  purpose  of  the  work  to  sift  from  the  multitudes 
of  devices  and  operations  which  have  been  advanced,  those  which  have 
so  stood  the  test  of  time  as  to  receive  the  endorsement  of  continued 
application  by  the  most  skilled  and  experienced  prosthetists,  and  to 
describe  in  detail  those  principles  which  are  applicable  to  the  greatest 
number  of  cases.  From  the  beginning  of  dental  journalism  the  pages 
of  periodicals  have  teemed  with  processes  conceived  and  advanced  with 
the  avowed  purpose  of  time-saving.  A  careful  examination  and  test 
of  such  methods  has  exhibited  one  strikingly  common  feature — namely, 
that  economy  of  time,  when  made  the  main  purpose,  is  generally  effected 
at  the  expense  of  accuracy.  The  demand  for  precision  is  quite  as 
imperative  in  dental  prosthesis  as  in  any  other  art,  and  it  is  evident, 
therefore,  that  the  saving  of  time  should  be  made  a  subordinate  motive. 
These  observations  apply  with  peculiar  force  to  the  department  of  arti- 
ficial crowns  and  bridge-work.  The  past  twenty-five  years  have  created 
in  these  subjects  alone  a  literature  embracing  sufficient  material  to  make 
a  volume  much  larger  than  this.  Such  literature  has  been  carefully 
examined,  and  is  here  reduced  from  its  many  ramifications  into  basal 
principles  and  their  embodiments,  wdiich  will  be  found  to  include  all 
those  devices  which  have  merited  and  found  actual  and  continued 
clinical  use. 

Prosthetic  Dentistry,  it  is  almost  needless  to  state,  is  more  than  a 
mere  mechanical  art,  for,  contrary  to  the  nature  of  such  arts,  there 
are  but  few  entirely  constant  rules  upon  wdiich  its  practice  may  be 
based.  Rarely  is  any  operation  in  this  art  an  exact  repetition  of  a  pre- 
ceding one,  the  resemblance  which  one  case  bears  to  another  being 
more  often  remote  than  close.  The  taste,  experience,  and  judgment 
required  for  the  proper  practice  of  prosthetic  dentistry  place  it  in  near 
kinship  with  one  of  the  fine  arts. 

Full  credit  for  sources  of  information  has  been  accorded  by  the  con- 
tributors in  their  several  chapters.  In  addition  to  these,  the  Editor 
tenders  his  grateful  thanks  for  favors  and  courtesies  extended  by  Prof. 
S.  H.  Guilford,  Dr.  John  N.  Farrar,  Dr.  Eugene  S.  Talbot,  Prof."  E.  H. 
Angle,  Dr.  Norman  W.  Kingsley,  Prof.  E.  C.  Kirk,  and  especially  to 
Prof.  H.  H.  Burchard  for  assistance  rendered  in  the  editorial  w'ork  and 
in  the  revision  of  proofs ;  also  to  Dr.  N.  S.  Essig  for  his  valuable  assist- 
ance in  the  preparation  and  revision  of  illustrations. 

Acknowledgment  of  obligation  and  thanks  are  due  and  proiFered  to 
the  S.  S.  White  Dental  Manufacturing  Co. ;  the  Buffalo  Dental  Manu- 
facturing  Co. ;    the   Wilmington   Dental   Manufacturing  Co. ;    and   to 

Messrs.  Johnson  &  Lund. 

CHAKLES  J.  ESSIG. 
Philadelphia,  August,  1896. 


LIST  OF  CONTRIBUTORS. 


HENKY  H.  BURCHAED,  M.  D.,  D.  D.  S., 

Special  Lecturer  on  Dental   Pathology  and   Therapeutics,   Philadelphia   Dental 
College,   Philadelphia. 

CHAELES  J.  ESSIG,  M.  D.,  D.  D.S., 

Professor  of  Mechanical  Dentistry  and  Metallurgy,  Department  of  Dentistry,  Uni- 
versity of  Pennsylvania,  Philadelphia. 

W.  W.  EVANS,   D.  D.  S.,   Washington,  D.  C. 

C.  L.  GODDARD,  A.  M.,  D.  D.  S., 

Professor  of   Orthodontia,    College   of   Dentistry,   University  of   California,   San 
Francisco. 

GEANT  MOLYNEAUX,  D.  D.  S., 

Professor  of  Prosthetic  Dentistry  and  Metallurgy,  Ohio  College  of  Dental  Surgery, 
Cincinnati. 

RODEIGUES  OTTOLENGUI,   M.  D.  S.,   New  York, 
Editor  of  the  "  Items  of  Interest." 

AMBLEE  TEES,  Jr.,  D.  D.  S., 

Lecturer  on  the  Continuous-gum  Method,  Department  of  Dentistry,  University  of 
Pennsylvania,  Philadelphia. 

ALTON  HOWAED  THOMPSON,  D.  D.  S., 

Professor  of  Dental  Anatomy,  Kansas  City  Dental  College,  Kansas  City,  Mo. 


CONTENTS. 


CHAPTER  I. 

PAGE 

THE    DENTAL    LABORATOEY :     ITS    EQUIPMENT    AND    ARRANGE- 
MENT . 17 

By  Chaeles  J.  Essig,  M.  D.,  D.  D.  S. 

CHAPTER  II. 

METALS  AND  ALLOYS  USED  IN  PROSTHETIC  DENTISTRY 74 

By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 

CHAPTER  III. 

PRINCIPLES  OF  METAL  WORK 153 

By  C.  L.  Goddard,  A.  M.,  D.  D.  S. 

CHAPTER  IV. 

MOULDING  AND  CARVING  PORCELAIN  TEETH 210 

By  Charles  J.  Essm,  M.  D.,  D.  D.  S. 

CHAPTER  V. 

THE  PREPARATION  OF  THE  MOUTH  ;   CHOICE  OF  MATERIAL  AND 

TYPE  OF  DENTURE 270 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 

CHAPTER  VI. 

TAKING  IMPRESSIONS  OF  THE  MOUTH 277 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 

CHAPTER  VII. 

MAKING  OF  MODELS,  AND  THEIR  PREPARATION 297 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 

CHAPTER  VIII. 

DIES,  COUNTER-DIES,  AND  MOULDING 309 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 

13 


14  CONTENTS. 

CHAPTER  IX. 

PAGE 

SWAGED  METALLIC  PLATES 319 

By  H.  H.  Burchaed,  M.  I).,  D.  D.  S. 

CHAPTER  X. 

THE  "BITE"  OK  OCCLUSION 346 

By  Grant  Molyneaux,  M.  D.,  D.  D.  S. 

CHAPTER  XL 

SELECTING   AND  FITTING    THE   TEETH ;    ATTACHMENT    TO    THE 

PLATE;  FINISHING 398 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 

CHAPTER  XII. 

ENGLISH   TUBE    TEETIi :    THEIR    USE    IN    PLATE-,    CROWN-,    AND 

BRIDGE-WORK 430 

By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 

CHAPTER  XIII. 

CONTINUOUS-GUM  DENTURES 446 

By  Ambler  Tees,  D.  D.  S. 

CHAPTER  XIV. 

CAST  DENTURES  OF  ALUMINUM  AND  FUSIBLE  ALLOYS 468 

By  C.  L.  Goddard,  A.  M.,  D.  D.  S. 

CHAPTER  XV. 

VULCANIZED  RUBBER  AS  A  BASE  FOR  ARTIFICIAL  DENTURES   .    .    479 
By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 

CHAPTER  XVI. 

CELLULOID  AND  ZYLONITE 553 

By  W.  W.  Evans,  M.  D.,  D.  D.  S. 

CHAPTER  XVII. 

THE    TEMPERAMENTS   AND    THE  TEMPERAMENTAL  CHARACTER- 
ISTICS OF  THE  TEETH  IN  RELATION  TO  DENTAL  PROSTHESIS  .    578 
By  Alton  Howard  Thompson,  D.  D.  S. 

CHAPTER  XVIII. 

ARTIFICIAL  CROWNS 588 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 


CONTENTS.  15 

CHAPTER  XIX. 

PAGE 

THE  ASSEMBLAGE  OF  UNITED  CKOWNS  (BKIDGE-WORK) 648 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 

CHAPTER  XX. 

HYGIENIC  RELATIONS  AND  CARE  OF  ARTIFICIAL  DENTURES  ...    702 
By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 

CHAPTER  XXI. 

PALATAL  MECHANISM 712 

By  Rodrigues  Ottolengui,  M.  D.  S. 


PROSTHETIC  DENTISTRY. 


CHAPTER   I 


THE  MECHANICAL  LABORATORY,  ITS  EQUIPMENT  AND 
ARRANGEMENT. 

By  Chaeles  J.  Essig,  M.  D.,  D.  D.  S. 


It  is  highly  important  that  the  furniture  and  equipment  of  a  dental 
laboratory  should  be  neat,  appropriate,  and  adapted  especially  to  the 
comfort  of  the  workman  and  to  cleanliness  and  celerity  in  his  manipula- 
tions. In  order  to  correct  the  want  of  uniformity  in  methods  and  results 
which  is  a  noticeable  feature  of  the  average  dental  laboratory  operations, 
students  should  in  the  very  beginning  be  taught  to  be  systematic  in  the 
care  of  tools  and  instruments,  as  well  as  in  all  the  manipulative  stages  of 
their  work.  They  should  be  required  to  find  suitable  places  for  every 
article  which  enters  into  laboratory  work,  so  that  when  not  in  use  tools 
and  apparatus  should  be  returned  to  the  places  assigned  them. 

The  usual  equipment  of  a  dental  laboratory  consists  in  a  suitable 
work-bench  carefully  adapted  to  the  purposes  for  which  it  is  to  be  used ; 
a  moulding-box  ;  plaster-table  and  sink  ;  a  swaging-block  and  anvil ;  at 
least  two  lathes,  one  designed  especially  for  the  grinding  and  fitting  of 
teeth,  the  other  for  finishing  and  polishing  only  ;  a  mechanical  blowpipe 
table,  supplied  with  gas-burner  on  the  Bunsen  principle,  of  sufficient 
capacity  to  allow  of  the  soldering  of  full  dentures. 

In  addition  to  these  permanent  articles  of  laboratory  furniture  it  will 
be  necessary  to  provide  a  suitable  furnace  for  the  melting  of  zinc,  lead, 
and  alloys  commonly  used  in  making  dies  and  counter-dies,  and  also 
another  and  different  one  to  be  used  for  the  occasional  melting  of  gold 
and  silver  and  in  the  formation  of  alloys  to  be  used  as  solders. 

The  accessories  of  soldering,  moulding  rings  and  flasks,  ingot-moulds, 
rolling-mills,  draw-plates,  pickling  solutions,  with  the  most  suitable  ves- 
sels for  holding  the  same,  grinding  and  polishing  materials,  fluxes, 
varnishes,  adhesive  wax,  and  bench  tools,  all  necessarily  form  part  of 
the  equipment  of  the  dental  laboratory,  and  will  each  be  separately 
described  in  these  pages. 

The  ivork-bench  should  be  constructed  of  cherry,  ash,  or  well-seasoned 
oak :  it  should  be  provided  with  not  less  than  two  sets  of  drawers,  as 

2  17 


18 


THE  MECHANICAL  LABORATORY. 


shown  in  the  diagram,  the  two  lower  ones  (Fig.  1,  A)  being  reserved  for  the 
reception  respectively  of  gold  and  silver  scraps  and  filings,  while  the 
upper  drawers  (Fig.  1,  B)  will  be  found  convenient  for  the  reception  of  the 
ordinary  bench  tools,  such  as  pliers,  shears,  plate-punches  and  cutters, 
horn  mallet,  etc.  The  drawers  (A)  should  be  20  inches  long  by  15  inches 
wide,  inclusive,  and  should  consist  of  a  frame  of  cherry  or  oak  2  inches 
wide  by  1  inch  thick  and  a  tray  (C)  of  tin  or  zinc  1  inch  in  depth.  By 
this  means  the  workman  is  provided  with  a  spacious  tray  Avhich  he 

Fig.  1. 


draws  out  to  cover  his  lap  in  a  manner  to  catch  the  filings  and  cuttings 
of  the  precious  metals  while  he  works. 

The  height  of  the  work-bench  should  be  about  34  inches,  and  in 
length,  when  designed  for  the  convenience  of  two  workmen,  about  5  feet 
6  inches ;  the  width  may  be  24  inches.  The  top  should  be  2  inches  in 
thickness,  and  immediately  over  the  tool-drawers  (B)  should  be  arranged 
a  rest  for  convenience  in  filing  and  finishing.  These  rests  are  usually 
made  of  the  same  hard  wood  as  the  top  of  the  bench,  2  inches  wide  and 
about  3  inches  long,  tapering  from  1^  inches  in  thickness  where  it  is 
mortised  into  the  table  to  ^  an  inch  at  its  extremity.     (See  Fig.  1,  D.) 

Accessories  of  the  Worh-hench. — A  good  vise  is  an  important  adjunct 
to  the  work-bench,  and  is  indispensable  wdien  the  draw-plate  is  used  for 
reducing  the  size  of  gold,  platinum,  or  silver  wdre. 

Rubber  slabs  of  \  an  inch  in  thickness  by  6  inches  square  afford 
excellent  rests,  not  only  for  the  protection  of  the  top  of  the  bench  from 
injury  by  contact  with  dies  and  counter-dies  in  the  preliminary  stage  of 
plate-making,  but  also  as  pliant  and  elastic  rests  for  the  metallic  or  rub- 
ber denture  during  stoning  and  finishing. 

Moulding-box. — This  article  of  laboratory  furniture,  shown  by  Fig.  2, 
demands  special  attention  in  its  construction,  otherwise  it  will  prove  a 
constant  annoyance,  as  no  ordinary  wooden  box  will  remain  tight  enough 
to  prevent  the  moulding  sand  from  falling  through  its  seams  upon  the 
floor.  The  diagram  shows  the  general  design  of  one  which  has  been 
found  practical  and  convenient.  It  is  4  feet  long,  26  inches  wide,  and  36 
inches  high.  It  is  lined  icifh  sheet  zinc,  which  does  not  rust  by  contact 
with  the  moist  sand,  and  eifectually  prevents  the  escape  of  the  latter.  It 
is  provided  with  a  shelf  (A),  upon  which  each  completed  mould  may  be 
placed  while  others  are  being  prepared  or  until  ready  for  the  casting.  It 
has  two  drawers  (B),  18  inches  Avide  by  4  inches  deep,  in  which  may  be 
kept  either  plaster  or  the  smaller  moulding-flasks,  rings,  and  other  acces- 


MOULDING-BOX  AND  ACCESSORIES. 


19 


'sories  of  the  moulding  operation.  It  is  provided  with  a  lid,  and  should 
be  kept  closed  when  not  in  use,  so  as  to  exclude  all  foreign  substances 
which  might  seriously  interfere  with  casting. 

Accessories  of  the  moulding-box  consist  of  the  various  sizes  of  the 
"  Bailv  moulding-flask,"  which,  with  the  method  of  using  them,  will  be 
described  under  the  head  of  dies  and  counter-dies  ;  one  Hawes  flask  (see 
page  313)  and  two  or  three  sections  of  galvanized  iron  stove-piping,  each 
having  the  dimensions  of  about  6  inches  in  length  by  41  inches  in  diam- 
eter. This  simple  form  of  flask  is  very  desirable  for  many  moulding 
operations  of  the  dental  laboratory,  its  value  consisting  in  the  fact  that  it 
will  accommodate  all  si2;es  of  models,  and  that  it  is  less  liable,  on  account 
of  the  greater  quantity  of  moulding  sand  required  by  it,  to  the  "bubbling" 

Fig.  2. 


which  often  occurs  when  melted  zinc  is  poured  in  contact  with  the  scant 
and  tightly-packed  sand  in  the  "  Baily  flask." 

It  is  essential  that  all  moulding  operations  should  be  performed  upon 
perfectly  level  surfaces,  and  for  this  purpose  two  or  three  "  moulding- 
blocks"  of  seasoned  pine,  8  inches  square  by  2  inches  thick,  will  be 
found  convenient  aids.  In  order  to  avoid  lumpiness  and  to  secure 
uniformity  of  condition  in  the  sand  when  moistening  it  preparatory  to 
moulding,  a  sieve  of  not  less  than  12  inches  in  diameter,  with  meshes  of 
a  minimum  size  of  Jg-  of  an  inch,  will  be  found  of  value.  The  sieve  should 
be  formed  of  brass  or  copper  wire,  as  an  ordinary  iron-wire  sieve  will 
soon  become  useless  from  oxidation,  which  is  greatly  assisted  by  contact 
with  the  wet  moulding  sand.  A  painter's  brush,  1^  inches  in  diameter 
by  2  inches  in  length,  will  be  found  useful  and  convenient  for  the  pur- 
pose of  removing  adherent  particles  of  moulding  sand  from  the  surface 
and  interstices  of  the  plaster  model  each  time  it  is  drawn  from  the  sand 
matrix. 

Anvil  and  Swaging-block. — As  the  laboratory  is  often  situated  on 
an  upper  floor,  the  use  of  the  hammer  in  swaging  plates  may  be  the 
cause  of  much  annoyance  from  noise  and  vibration.  This,  however,  can 
be  entirely  avoided  by  interposing  rubber  between  the  block  and  the 
floor  upon  which  it  rests.     Fig.  3,  A,  shows  the  block  of  pine  or  poplar 


20 


THE  MECHANICAL  LABORATORY. 


wood,  7-|-  inches  square  by  23^  inches  high.  B  and  C  represent  a  sheet 
of  rubber  8|^  inches  square  by  1  ^  inches  thick,  securely  fastened  to  the 
lower  end  of  the  block  by  screws.  This  block  fits  into  a  box  made  of  1^- 
inch  pine  boards,  broader  below  than  above  (Fig.  4j  D),  furnished  with  a 
loose  bottom,  made  of  2-inch  seasoned  oak  or  ash,  and  provided  with  four 
pieces  of  solid  rubber  cylinder  (Fig.  3,  F)  1^  inches  in  diameter  by  2  inches 


Fig.  3. 


Fig.  4. 


Fig.  5. 


long,  let  into  it  by  holes  of  the  same  dimensions  bored  to  a  depth  of  1|- 
inches.  Two  thicknesses  of  rubber  are  thus  interposed  between  the  block 
upon  which  the  anvil  rests  and  the  floor  of  the  laboratory,  and  so  much 
of  the  sound  due  to  the  percussive  force  of  the  hammer  is  thereby  dead- 
ened that  scarcely  any  noise  or  vibration  will  be  observed  by  persons  in 
other  parts  of  the  house. 

The  anvil  (Fig.  5),  which  should  weigh  not  less  than  40  pounds, 
may  be  securely  fastened  to  the  block  upon  which  it  rests  by  strong  iron 

staples  (G),  and  the  box  or  outside  covering  of 
the  block  reinforced  by  iron  bands,  as  shown 
in  H.  A  swaging  block  so  constructed  may 
be  looked  upon  as  a  permanent  piece  of  labor- 
atory furniture,  and  one  that  will  not  be  likely 
to  get  out  of  order.  Two  swaging  hammers 
are  required — one,  weighing  about  2  pounds, 
is  of  much  use  in  starting  the  plate.  The 
heavier  one,  which  should  weigh  5|^  or  6 
pounds,  is  used  with  greater  force  after  the 
plate  has  been  made  to  partially  conform  to 
the  zinc  die  when  there  is  no  longer  danger 
of  its  pleating  or  folding. 

Plaster-table  and  Sink  (Fig.  6). — The  work- 
ing of  plaster,  which  forms  so  important  a  part 
of  the  operations  of  the  dental  laboratory,  is 
entitled    to    much    more    care    and    attention 
than  it  usually  receives  at  the  hands  of  the 
mechanical  dentist.     It  may  be  employed  with  neatness  and  precision, 
when  its  results  become  truly  artistic,  or,  as  is  too  often  the  case,  it  may 
be  handled  in  so  slovenly  and  untidy  a  manner  as  to  greatly  lower  the 


PLASTER-TABLE  AND  ACCESSORIES. 


21 


standard  of  results,  and,  unless  kept  carefully  within  the  precincts 
assigned  it,  cause  the  laboratory  to  become  a  most  unattractive  place. 
It  is  of  importance,  therefore,  that  a  suitable  table  be  provided  upon 
which  the  casting  and  subsequent  trimming  of  plaster  models  and  other 
parts  of  the  laboratory  work  depending  upon  the  employment  of  plaster 
may  be  performed.  The  plaster-table  should  also  be  supplied  with  a 
sink  and  receptacle  for  the  cuttings  and  refuse  fragments.  The  accom- 
panying diagram  shows  such  a  table  and  sink  which  the  author  has 
found  to  be  practical  and  convenient.  It  has  been  designed  especially 
to  protect  the  floor  and  other  parts  of  the  laboratory  from  contact  with 
plaster.  It  is  31  inches  high,  23  inches  wide,  and  27  inches  long,  and 
has  an  opening  (A)  8  inches  by  8  inches  square,  under  which  rests  a 


Fig.  6. 


Fig.  7. 


portable  box  (C),  12  by  12  inches  square,  intended  to  receive  all  cuttings 
and  refuse  plaster. 

The  table  is  provided  with  a  small  rest  (B)  for  convenience  in  resting 
the  model  while  trimming  to  proper  dimensions.  It  is  also  provided 
with  a  drawer  for  the  reception  of  plaster  knives,  spatulas,  and  camel's- 
hair  brushes  used  in  mixing  plaster  and  in  casting  and  trimming  models. 

The  accessories  of  the  plaster-table,  named  in  the  order  in  which  they 
are  used,  consist,  first,  of  two  short  broad-necked  bottles,  for  sandarac 
and  shellac  varnish,  two  or  more  flexible  rubber  plaster  bowls,  the  same 
number  of  bone,  ivory,  or  steel  spatulas  for  mixing,  one  or  more  "  plaster 
knives,"  such  as  are  sold  at  the  dental  depots  for  the  purpose  of  reducing 
the  size  of  plaster  models,  or  a  bench-knife,  as  shown  in  Figs.  7,  8,  will 
be  found  very  effective  in  cutting  down  hard  plaster  in  preparing  the 
model  for  flasking  in  rubber  or  celluloid  work,  and  a  number  of  different 
sizes  of  camel's-hair  brushes,  which  are  indispensable  in  carrying  the 
plaster  into  the  deeper  parts  when  running  or  casting  impressions  for 
partial  dentures,  and  indeed  all  impressions  having  deep  and  more  or 
less  inaccessible  points,  which  might  not  be  perfectly  reached  by  the 
gravitation  of  the  plaster  unassisted  by  some  such  means  as  is  suggested 
by  the  use  of  the  camel's-hair  pencils  or  brushes. 

Two  kinds  of  varnish  are  usually  employed  in  the  preparation  of  the 
surfaces  of  impressions  for  running  out  the  models^  so  as  to  prevent  too 


22  THE  MECHANICAL  LABORATORY. 

close  adhesion  of  one  to  the  other.  One  is  transparent  and  dries  upon 
the  plaster  without  color.  The  other  is  of  the  color  of  burnt  sienna,  and 
imparts  a  dark-yellow  stain  to  the  plaster.  The  first  is  made  by  dissolving 
5  ounces  of  gum  sandarac  in  a  quart  of  alcohol.  The  latter  is  formed  of 
gum  shellac  and  alcohol  in  the  same  proportions.  Gum  sandarac  dis- 
solves rather  slowly,  and  requires  a  good  quality  of  alcohol  free  from  a 
very  considerable  percentage  of  water ;  otherwise  it  will  have  a  milky 
appearance  and  will  not  afford  a  perfectly  glazed  surface  when  applied 
to  the  plaster  impression.  These  two  varnishes  are  employed  for  totally 
different  purposes.  In  running  out  an  impression  the  object  should  be 
to  obtain  a  perfect  surface  to  the  model,  one  that  is  free  from  air-bells 
or  roughness  of  any  kind,  as  such  imperfections  will  be  represented  on 
rubber  or  celluloid  dentures  by  multitudes  of  minute  globules  which  are 
highly  irritating  to  the  mucous  membrane  of  the  mouth.  The  shellac 
varnish  should  be  applied  first,  as  it  penetrates  the  plaster  and  discolors 
it  sufficiently  to  serve  as  a  guide  in  removing  impressions  from  models, 
and  thus  prevents  the  workman  from  injuring  the  teeth  or  prominent 
parts  of  the  model.  After  the  shellac  varnish  has  been  allowed  to  dry 
the  sandarac  should  be  applied  with  a  camel's-hair  brush  until  the  sur- 
face is  glazed.  It  should  be  laid  on  of  a  uniform  thickness,  but  not  in 
such  quantity  as  to  fill  up  deep  places  or  to  injure  the  correctness  of  the 
fac-simile  of  the  mouth. 

After  the  last  coat  of  varnish  has  been  allowed  to  dry,  if  the  glazing 
of  the  surface  is  satisfactory,  the  plaster  impression  merely  requires  to  be 
dipped  in  water  to  ensure  saturation  and  to  further  harden  the  varnish, 
when  it  is  ready  for  running  the  model.  Careful  attention  to  these  details 
will  produce  a  model  possessing  hardness  of  surface  and  with  the  glazed 
appearance  which  is  noticed  when  plaster  is  poured  and  allowed  to  set 
upon  glass.  This  result,  however,  cannot  be  obtained  when  oil  or  solu- 
tions of  soap  have  been  used  :  such  substances  should  never  be  applied 
to  plaster  impressions,  as  they  do  not  afford  surfaces  sufficiently  smooth 
or  hard  upon  which  to  form  rubber  or  celluloid  dentures.  To  get  the 
best  results  in  the  handling  of  plaster,  the  latter  in  mixing  should  be 
slowly  dropped  into  water  until  it  becomes  saturated  and  settles  to  the 
bottom  of  the  bowl,  so  as  to  expel  the  air.  The  surplus  of  water  is  then 
poured  off  and  the  plaster  well  stirred,  when  it  should  be  carried  to  the 
surface  of  the  impression  and  into  the  deep  parts  with  a  camel's-hair 
brush,  and  the  balance  built  up  with  the  spatula. 

Plaster  of  Paris  (calcium  sulphate,  CaSOJ  is  prepared  from  a  native 
calcium  sulphate,  containing  two  molecules  of  w^ater  of  crystallization 
(CaSOi+  2H2O),  called  gypsum  when  found  in  opaque  masses,  alabaster 
when  it  presents  a  semi-opaque  appearance,  and  selenite  when  it  occurs 
in  transparent  prisms.  The  first  is  the  common  source  of  plaster  of  Paris. 
It  is  prepared  by  heating  the  mineral  in  an  oven  where  the  heat  does 
not  exceed  127°  C.  (261°  F.),  by  which  the  water  of  crystallization  is 
expelled.  It  is  afterward  reduced  to  a  fine  powder,  and  when  mixed 
with  water  it  solidifies  after  a  short  time  from  the  re-formation  of  the 
same  hydrate ;  but  this  effect  does  not  happen  if  the  gypsum  has  been 
overheated  and  its  affinity  for  water  destroyed.  In  setting  there  is  always 
a  slight  evolution  of  heat  and  more  or  less  expansion. 

For  dental  purposes  there  should  be  two  kinds  of  plaster  provided. 


THE  CARE  OF  METALS.  23 

For  taking  impression  of  the  mouth,  a  finely-ground  plaster  is  re- 
quired, which  sets  quickly,  but  does  not  become  hard  enough  to  demand 
a  very  considerable  exhibition  of  force  in  its  fracture,  which  is  nearly 
always  unavoidable  in  removing  impressions  of  mouths  containing  natural 
teeth  and  perhaps  several  dovetailed  interdental  spaces. 

A  different  quality  of  plaster  is  demanded  for  running  models  and 
in  vulcanite  and  celluloid  work,  which  need  not  necessarily  possess 
the  quick-setting  property,  but  in  which  greater  hardness  and  strength 
are  indispensable  requirements.  (See  page  298.)  Plaster  when  not  being 
used  should  be  kept  covered  to  shield  it  from  occasional  dampness  of  the 
atmosphere  and  to  protect  it  from  water  and  foreign  substances  which 
might  accidentally  fall  into  it.  The  tin  cans  in  which  plaster  is  furnished 
by  the  dental  depots  are  admirably  suited  for  this  purpose,  and  no  im- 
provement over  them  need  be  looked  for. 

Care  of  Metals  used  in  the  Formation  of  Dies  and  Counter-dies. — 
Zinc  and  lead  are  the  metals  most  frequently  employed  for  this  purpose, 
but  there  are  also  several  alloys  which  have  found  favor  with  some  of  our 
most  skilful  and  experienced  mechanical  dentists.  The  composition, 
fusing-points,  and  physical  properties  of  all  of  these  will  be  described  in 
another  chapter.  There  are  other  alloys  used  in  crown-  and  bridge- 
work,  and  these  demand  special  care  in  their  storage  and  handling. 
First,  it  is  important  that  they  be  kept  strictly  apart  and  that  separate 
melting-pots  or  ladles  be  provided  for  each.  This  is  especially  true  with 
regard  to  zinc  and  lead,  two  metals  which  resemble  each  other  so  closely 
that  it  may  easily  happen  that  a  zinc  die  be  remelted  in  a  pot  already 
partly  full  of  lead.  The  necessity  for  carefully  keeping  these  two  metals 
separate  in  all  moulding  operations  will  readily  be  appreciated  when  it  is 
remembered  that  zinc  and  lead  combine  with  each  other  to  a  very  limited 
extent,  and  that  when  melted  together  and  allowed  to  cool  they  separate 
in  two  layers,  the  upper,  and  consequently  the  lighter  one,  zinc,  retaining 
1.2  per  cent,  of  the  lead,  while  the  lower  layer  consists  of  lead  alloyed 
with  1.6  per  cent,  of  zinc.  If  by  accident  lead  becomes  mixed  with  zinc 
used  for  dies,  the  lead  by  its  greater  specific  gravity  settles  to  the  bottom 
and  fills  up  the  deeper  portions  of  the  sand  matrix  representing  the 
alveolar  ridge,  the  most  prominent  part  of  the  die.  This  may  not  be 
discovered  until  an  attempt  to  swage  is  made,  when  the  die  will  be  found 
to  be  totally  unfit  for  the  purpose.  In  such  cases  the  mixed  metal  should 
be  discarded  and  new  zinc  substituted.  Lead  belongs  to  a  small  class  of 
metals  which  are  so  soft  that  they  can  be  scratched  by  the  finger-nail, 
while  zinc  is  so  much  harder  that  no  impression  can  be  made  upon  it 
by  that  means.  This  simple  test  is  therefore  an  excellent  way  of 
deciding  between  lead  and  zinc  as  they  appear  in  the  pot  or  ladle  after 
having  been  previously  melted. 

In  casting  metals  of  the  class  to  which  zinc  and  lead  belong  their 
fusing-point  should  be  borne  in  mind,  so  that  they  may  not  be  subjected 
to  temperatures  greatly  in  excess  of  that  which  is  sufficient  to  melt  them; 
otherwise  partial  oxidation  will  occur,  which  greatly  impairs  the  working 
qualities  of  the  metals  by  rendering  them  viscid  and  difficult  to  pour 
when  fused,  and  so  brittle  after  casting  as  to  be  unfit  to  bear  the  blows 
of  the  swaging  hammer  without  breaking. 

While  the  metals  used  in  the  formation  of  dies  and  counter-dies  are 


24 


THE  MECHANICAL  LABORATORY. 


melting  they  should  be  watched,  and,  when  the  last  solid  portion  becomes 
fluid,  removed  from  the  furnace  and  allowed  to  stand  for  a  few  moments 
until  the  fused  metals  are  observed  to  crystallize  at  the  edges,  when  they 
are  in  the  proper  condition  for  casting ;  for  when  zinc  or  lead  are  poured 
at  a  temperature  greatly  in  excess  of  their  fusing-points  the  shrinkage 
of  the  die  is  not  only  greater,  but  the  amount  of  vapor  generated  by 
contact  with  the  moist  moulding  sand  is  very  likely  to  cause  "  bubbling," 
which  is  nearly  always  fatal  to  the  die. 

The  Precious  Metals. — Scraps  and  filings  of  the  precious  metals,  such 
as  gold,  platinum,  and  silver,  shoidd  be  kept  free  from  contamination 
with  particles  of  zinc,  lead,  or  tin,  which  metals  are  constantly  being 
used  about  the  work-bench,  while  at  the  same  time  admixture  with  each 
must  be  avoided.  Small  pieces  of  pattern  tin  or  fragments  cut  from 
dies  and  counter-dies,  when  overlooked  and  melted  with  either  gold,  sil- 
ver, or  platinum,  reduce  their  fusing-points,  lessen  or  destroy  ductility 
and  malleability,  and  greatly  modify  color.  With  the  utmost  care  it  is 
almost  impossible  to  maintain  the  standard  of  these  metals,  and  a 
remelting  of  scraps  and  filings  of  gold  taken  from  the  drawer  of  the  work- 
bench will  always  be  found  to  be  below  the  grade  of  the  plate  from 
which  they  were  cut :  this  is  partly  due  to  impurities  such  as  have  been 
referred  to,  fragments  of  steel  from  the  files  used,  and  the  solder 
employed  in  the  construction  of  the  plate,  more  or  less  of  which  in- 
variably finds  its  way  into  the  gold  drawer  in  reducing  the  plate  to  its 
proper  dimensions.  When  it  becomes  necessary  to  remelt  scraps  for  the 
construction  of  backings,  for  instance,  filings  should  be  excluded  alto- 
gether, and  only  clean  scraps,  free  from  solder,  should  be  selected. 

Modes  of  Melting  Metals. — The  means  employed  for  this  purpose 
will  depend  upon  the  character  of  the  metal  or  alloy  to  be  fused.  The 
fusing-point  of  such  alloys  as  are  used  for  dies  and  counter-dies  in 
crown-  and  bridge- work,  which  melt  at  temperatures  ranging  from  1 58°  F. 
to  236°  F. — and  there  are  no  less  than  six  of  these  alloys  now  in  use — 
may  be  accomplished  by  simply  placing  a  sample  of  any  one  of  them  in 
a  small  iron  ladle  provided  with  a  suitable  handle,  and  holding  it  over  a 
gas-jet  or  the  flame  of  an  alcohol  or  oil  lamp,  or,  in  the  case  of  zinc, 

lead,  or  Babbitt's  metal,  in  an  ordinary  stove 
Fig.  9.  or  furnace,  or,  better  still,  when  gas  is  avail- 

able, by  one  of  the  gas-furnaces  devised  by  Mr. 
Fletcher  of  Warrington,  England,  for  melting 

Fig.  10. 


zinc  and  lead  for  dies  and  counter-dies  and  for  the  fusion  of  all  alloys 
which  may  be  melted  in  an  iron  ladle  at  or  below  red  heat. 


MODES  OF  MELTING  METAL. 


25 


Fig.  11. 


Figs.  9  and  10  show  an  improved  form  of  furnace  with  ladle  for 
melting  zinc,  lead,  and  other  metals  for  dies  and  counter-dies,  which  is 
believed  to  be  a  better  furnace  for  that  purpose  than  any  other  yet 
made.  It  works  equally  well  with  any  gas-supply  available  ;  the  speed 
of  working  is,  however,  proportionate  to  the  supply  of  gas.  The  burner 
can  be  removed  from  the  casing  and  used  for  other  purposes  if  desired. 

When  gas  is  not  available,  the  gasoline  furnaces  used  by  plumbers  for 
melting  solder  have  no  superiors  in  point  of  convenience  and  rapidity, 
while  the  cost  of  the  fuel  is  very  slight.  Fig. 
11  gives  an  illustration  of  this  furnace.  The 
lower  portion  is  a  galvanized  reservoir  which 
holds  the  gasoline.  In  the  top  of  the  reser- 
voir Is  a  stopcock  with  a  short  rubber  tube 
attached,  through  which  air  is  forcibly  blown 
for  a  moment  until  pressure  is  made  upon 
the  surface  of  the  gasoline,  which  forces  it 
out  through  a  tube  continuous  with  the 
supply-tube  of  the  burner  reaching  from 
the  bottom  of  the  tank,  and  conveys  it  to  the 
burner,  the  supply  to  which  is  regulated  by  a 
valve.  The  burner  is  so  constructed  that  the 
flame  from  the  burning  jet  of  gasoline  is  pro- 
jected upon  a  recurved  portion  of  the  supply- 
tube,  which  is  heated  thereby  to  a  tempera- 
ture sufficient  to  vaporize  the  gasoline  before 
it  makes  its  exit  at  the  jet.  The  result  is  a  large  volume  of  gasoline  vapor 
under  high  pressure,  burning  with  an  intensely  hot  flame,  without  any  dis- 
agreeable odor,  and  with  more  than  ample  heating  power  for  the  require- 
ments of  the  case.  When  once  started  the  action  is  perfectly  automatic. 
The  cast-iron  shell  around  the  burner  directs  the  heat  toward  the  sides  of 
the  melting-ladle,  which  stands  within  it  and  upon  a  support  immediately 
above  the  flame.  A  gauze  packing  in  the  exit-tube  interposed  between 
the  burner  and  the  gasoline  reservoir  prevents  any  danger  of  ignition  of 
the  fluid  in  the  latter  while  the  furnace  is  in  action.  The  form  of  this 
furnace,  made  by  C.  Gefrorer,  Philadelphia,  is  admirably  adapted  for  use 
with  the  Baily  melting-pots  commonly  used  in  the  dental  laboratory. 

"The  oxycarbon  dental  furnace"  (Fig.  12),  for  use  by  dentists 
who  are  located  where  gas  is  unattainable,  will  be  recognized  as  an 
improved  form  of  the  preceding  furnace.  It  gives  a  strong,  steady, 
and  continuous  heat,  the  flame  being  smokeless  and  nearly  odorless, 
and  is  capable  of  continuous  use,  if  required,  without  any  attention 
save  an  occasional  compression  of  the  rubber  bulb  to  keep  up  the  pres- 
sure upon  the  contents  of  the  reservoir.  When  put  to  continuous  use 
for  a  day  it  will  consume  about  half  a  gallon  of  gasoline.  It  is  claimed 
for  this  furnace  that  it  is  entirely  efl^ective  in  the  melting  of  gold  or  sil- 
ver, preparing  zinc  dies,  annealing  plates,  heating  up  invested  dentures 
preparatory  to  soldering,  and  for  all  purposes  of  the  dental  laboratory 
requiring  strong  heat. 

It  should  be  remembered  that  zinc  will,  under  favorable  conditions, 
unite  with  iron,  and  it  frequently  attacks  the  cast-iron  ladle  in  which  it 
is  melted,  and  may  penetrate  the  side  and  escape  into  the  fire.     Accidents 


26 


THE  MECHANICAL  LABORATORY. 


of  this  kind  are  more  likely  to  occur  when  the  ladle  is  new,  and  may  be 

avoided  by  coating  the  inside  with  whiting  previous  to  the  first  melting. 

The   melting  of  metals  which  require  very  high  temperatures  must 

necessarily  be  accomplished  in  crucibles.  These  are  made  of  clay  with 


Fig.  12. 


The  carbon  furnace. 


admixture  of  silica,  burnt  clay,  graphite,  or  other  infusible  material.  A 
crucible  should  possess  the  power  of  resisting  high  temperatures  without 
fusing  or  softening.  It  should  also  be  capable  of  retaining  sufficient 
strength  when  hot  to  prevent  its  crumbling  or  breaking  when  grasped 
by  the  tongs.  Lastly,  it  should  not  crack  either  in  heating  or  cooling. 
For  the  fusing  of  platinum,  which  requires  the  intense  heat  of  the 
oxyhydrogen  flame,  they  are  formed  of  blocks  of  thoroughly  burned 
lime.  The  furnace  usually  employed,  shown  in  Fig.  105,  also  serve& 
the  purpose  of  a  crucible.  In  form  it  may  be  described  as  a  sort 
of  basin  or  concavity  with  a  similar  piece  for  a  cover.  The  lower 
part  is  intended  for  the  reception  of  the  metal ;  through  the  centre  of 
the  upper  portion  or  cover  pass  the  tubes  for  the  oxyhydrogen  jet, 
while  the  lower  portion  is  provided  with  a  lip  or  spout  for  pouring 
the  melted  metal.  The  tubes  which  pass  through  the  top  for  the 
transmission  of  the  two  gases  are  generally  formed  of  copper  with 
platinum  tips.  The  outer  and  lower  tube  carries  hydrogen,  while 
the  inner  and  upper  one  carries  a  jet  of  oxygen  into  the  middle  of  the 
flame.  The  tubes  are  furnished  with  stopcocks,  so  that  the  supply  may 
be  regulated.  When  the  object  is  merely  to  fuse  some  scraps  of  platinum, 
the  lime-furnace  is  first  put  together ;  the  hydrogen  jet  is  lighted ; 
oxygen  is  then  turned  on,  and  the  interior  of  the  apparatus  soon  becomes 
heated.  The  platinum  is  then  introduced  in  pieces  through  a  small  hole 
at  the  side,  and  quickly  fuses  after  entering  the  furnace. 

The  ingot-mould  used  in  casting  melted  platinum  is  usually  formed 


THE  OXYHYDROGEN  BLOWPIPE. 


27 


of  coke  or  pieces  of  lime  or  graphite,  and  the  furnace  is  arranged  on 
centres,  so  that  it  can  be  tilted  sufficiently  to  allow  the  fluid  metal  to  flow 
into  the  mould. 

The  form  of  oxyhydrogen  blowpipe  invented  by  Dr.  J.  R.  Knapp, 
shown  by  Fig.  13,  is  a  complete  and  etfective  apparatus  for  soldering  and 
melting  operations  in  the  dental  laboratory.  It  may  be  used  with  equal 
facility  in  soldering  the  largest  piece  of  plate-work  or  the  most  delicate 
crown-work,  and  is  of  particular  value  to  dentists  who  give  attention  to 
continuous-gum  work,  enabling  them  to  readily  remelt  their  platinum 

Fig.  13. 


scraps.  It  is  provided  with  an  iron  stand,  in  which  is  secured  by  a  thumb- 
screw a  100-gallon  cylinder  of  nitrous-oxide  gas.  By  means  of  a  yoke 
and  set-screw  the  valve  of  the  cylinder  is  connected  with  the  tubes  and 
valves  of  the  blowpipe  in  such  a  manner  that  the  proportions  of  a  mix- 
ture of  nitrous-oxide  and  illuminating  gases  are  under  perfect  regulation 
and  control.  A  cylinder  of  nitrous-oxide  gas  is  placed  in  the  base  or 
stand,  and  fastened  with  the  thumb-screw  A.  The  yoke  carrying  the 
stopcocks  and  valves  is  attached  to  the  valve  of  the  cylinder  and  tight- 
ened with  the  screw  B.  The  pipe  C  is  connected  by  a  rubber  tube  to  an 
illuminating-gas  bracket.  When  the  apparatus  is  in  use  the  illuminating 
gas  is  turned  on,  and  its  flow  regulated  by  the  handle  D.  The  handle  G 
over  the  outlet  H  is  then  turned  ;  the  cylinder  valve  is  opened  by  means 
of  the  hand-wheel  I  sufficiently  to  permit  the  escape  of  enough  nitrous- 
oxide  gas  to  be  detected  by  touching  the  opening  H  with  the  finger. 

When  the  desired  quantity  of  nitrous-oxide  gas  is  obtained,  the  flow 
is  directed  to  the  mixing  chamber  and  controlled  by  the  handle  G,  which, 
when  in  position,  as  shown  in  the  cut,  allows  the  gas  to  pass  freely  into 


28 


THE  MECHANICAL  LABORATORY. 


Fig.  14. 


the  chamber  K,  where  it  mixes  with  illuminating  gas.  Either  or  both 
of  the  burners  may  be  used  and  the  desired  flame  obtained  by  regulating 
the  pressure  of  the  gases  by  the  handles  controlling  them.  It  is  an  in- 
strument of  much  greater  delicacy  than  the  blowpipes  commonly  used  by 
dentists.  The  flame  which  it  affords  is  very  small,  but  the  intensity  of 
its  heat  is  such  that  great  care  must  be  exercised  in  soldering  small 
objects  to  prevent  "  burning "  or  even  entire  fusion  of  the  parts  ad- 
jacent to  the  solder.  It  is  economical  of  time  and  materials,  and  its 
perfect  cleanliness  will  commend  it  to  all  who  work  in  the  higher 
branches  of  mechanical  dentistry. 

Dr.  J.  H.  Downie  has  devised  a  neat  and  efficient  nitrous-oxide  blow- 
pipe (Fig.  14),  which  is  a  simplified  form  of  the  preceding.  The  advan- 
tages claimed  for  it  are  that  there  is  so 
little  force  required  for  the  blast  that  the 
solder  and  borax  are  never  blown  out 
of  place,  and  yet  the  heat  is  so  intense 
that  all  soldering  operations  of  the  den- 
tal laboratory  may  be  accomplished 
without  delay  or  the  least  difficulty,  and 
that  its  simplicity  prevents  any  part  of 
it  from  getting  out  of  order.  The  coal 
gas  is  supplied  by  connection  with  one 
of  the  tubes  shown  in  the  cut,  and  the 
nitrous  oxide  to  the  other.  The  amount 
of  nitrous-oxide  gas  required  is  so  small 
that  it  need  scarcely  be  taken  into  con- 
sideration. It  may  be  used  in  small 
places  where  there  is  no  supply  of  the 
ordinary  illuminating  gas  by  substituting 
a  carburetter  furnished  by  the  manu- 
facturers of  the  blowpipe,  which,  it  is 
claimed,  will  run  it  equally  as  well  as 
coal  gas. 

A  process  of  melting  platinum  for 
dental  purposes,  recently  devised  by 
Dr.  L.  E.  Custer  of  Dayton,  Ohio,  in 
which  electricity  is  the  active  agent  (Fig.  1 5),  is  described  by  the  inventor 
as  follows  :  "  The  production  of  heat  by  electricity  depends  upon  two  fac- 
tors— the  quantity  of  electricity  and  the  resistance  of  the  conducting  agent. 
As  the  quantity  is  increased  the  heating  power  is  augmented,  but  this 
power  is  not  apparent  until  the  current  meets  with  some  resistance.  The 
unobstructed  flow  of  any  quantity  of  the  fluid  does  not  produce  heat. 
It  is  only  when  there  is  placed  in  the  circuit  a  poor  conductor  of  elec- 
tricity that  we  have  this  manifestation. 

"  All  metals  are  comparatively  good  conductors  of  electricity,  yet 
they  vary  in  their  conducting  power,  copper  ^  representing  one  extreme 
and  German  silver  the  other.  The  size  of  the  wire  is  another  factor  in 
the  determination  of  heat :  with  a  given  length  of  wire  the  resistance 
increases  as  the  diameter  of  the  wire  decreases.     In  other  words,  a  small 

^  Silver  is  the  best  conductor  amongst  the  metals,  standing  first  in  the  list,  with  cop- 
per second.     The  alloys  are  generally  poor  conductors. 


PROCESS  OF  MELTING  PLATINUM. 


29 


wire  has  less  carrying  capacity  than  a  large  one,  so  that  when  the  same 
amount  of  current  that  is  easily  conducted  by  the  large  one  is  forced 
through  a  small  wire  resistance  is  met  with  and  heat  is  produced. 

Fig.  15. 


"When  a  current  has  been  established  by  bringing  two  terminals 
together,  the  electricity  continues  to  flow  even  after  the  ends  have  been 
separated.  It  leaps  the  intervening  space  and  forms  a  voltaic  arc.  The 
heat  of  the  arc  is  so  intense  that  it  is  practically  without  limit.  The 
method  herein  described  is  a  device  for  making  and  using  the  voltaic  arc 
for  melting  metals  which  are  infusible  at  ordinary  temperatures.  The 
appliance  is  adapted  to  the  110-volt  current,  that  which  is  used  for 
incandescent  lighting,  and  which  is  the  ideal  current  for  dental  purposes. 
A  large  quantity  of  current  being  necessary,  the  safety  plugs  should  be 
as  large  as  No.  16  or  18  standard  gauge.  A  resistance  coil  of  eight 
pounds  of  No.  18  copper  wire  will  prevent  fusing  the  plug  and  at  the 
same  time  give  a  large  arc.     This  is  placed  at  a  convenient  point  in  the 


30 


THE  MECHANICAL  LABORATORY. 


circuit.     It  becomes  heated,  and  should  be  insulated  and  ventilated  on 
asbestos  if  used  for  a  considerable  length  of  time. 

"  A  block  of  carbon,  such  as  is  used  in  batteries,  is  connected  with  one 
wire  for  the  receptacle  and  a  carbon  pencil  is  attached  to  the  other  wire. 
Carbon  is  used  for  the  receptacle  because  it  is  a  conductor  of  electricity, 
a  poor  conductor  of  heat,  is  non-combustible,  and  can  be  easily  fashioned 
to  mould  the  melted  metal.  The  carbon  pencil  is  to  be  used  by  the 
right  hand ;  it  is  made  of  an  electric-light  carbon  five  or  six  inches 
long.  A  hole  is  drilled  two-thirds  its  length,  and  in  this  hole  is  inserted 
the  other  terminal  wire.  This  wire  is  so  insulated  that  only  the  end 
€omes  in  contact  with  the  carbon.  By  this  arrangement  the  upper  two- 
thirds  of  the  pencil,  although  charged  electrically,  does  not  become 
heated  and  answers  for  a  handle.  The  platinum  is  laid  on  the  carbon 
bed  and  the  pencil  is  brought  in  contact  with  it.  Immediately  there  is 
a  current  established  from  the  pencil  through  the  platinum  to  the  carbon 
bed  or  vice  versa.  Upon  raising  the  pencil  a  short  distance  an  arc  is 
formed  directly  upon  the  metal  and  it  is  melted.  The  arc  can  be  carried 
about  at  will  until  the  pieces  are  all  brought  into  one  mass. 


Fig.  16. 


Fig.  17. 


Small  quantities  of  gold  or  silver  may  be  melted  by  means  of  the 
ordinary  blowpipe  upon  a  support  formed  of  charcoal.     A  good  solid 


PBOCESS  OF  MELTING   GOLD  AND  SILVER. 


31 


•cylindrical  piece  of  thoroughly  charred  pine  coal  should  be  selected,  and 
divided  into  two  equal  halves  by  a  vertical  cut  with  a  saw,  as  shown  by 
Figs.  16,  17,  18.  Upon  the  end  of  one  half  a  depression  should  be  cut 
for  the  reception  of  the  metal  to  be  melted  (A).  On  the  flat  side  of  the 
other  half,  extending  to  the  end,  the  ingot-mould  should  be  carved,  of  a 
size  and  shape  governed  by  the  requirements  of  the  case  (B).  The  two 
halves  should  then  be  brought  together  and  secured  by  a  piece  of  iron  or 
copper  wire,  when  they  will  be  found  to  practically  combine  the  require- 
ments of  a  crucible  and  ingot-mould. 

The  depression  in  which  the  metal  is  to  be  melted  and  the  mould  or 
receptacle  should  be  connected  by  means  of  a  gutter  or  groove.  The 
flame  of  the  blowpipe  is  directed  upon  the  metal,  and  when  thor- 
oughly fluid  the  charcoal  is  tilted,  so  that  the  fused  metal  will  run  into 
the  mould  prepared  for  it  in  the  opposite  half  of  the  charcoal.  This  is 
probably  the  simplest  form  of  apparatus  by  which  small  quantities  of 
metal  can  be  melted,  and  is  often  employed  in  the  dental  laboratory  and 
by  jewellers. 

Mr.  Fletcher  has  devised  an  apparatus  embodying  the  same  general 
principles  as  the  one  just  described  for  quickly  obtaining  ingots  of  gold 
and  silver  without  the  use  of  a  furnace  (Fig.  19):    A  representing  a 

Fig.  19. 


crucible  of  moulded  carbon,  supported  in  position  by  an  iron  side-plate ; 
B,  the  ingot  mould ;  C,  clamp  holding  ingot-mould  and  crucible  in  posi- 
tion ;  D,  cast-iron  stand  upon  which  the  latter  swivels.  The  metal  to  be 
melted  is  placed  in  the  crucible  (A),  and  the  flame  of  the  blowpipe  is 
directed  upon  it  until  it  is  perfectly  fused.  The  waste  heat  serves  to 
make  the  ingot-mould  hot.  The  whole  is  tilted  over  by  means  of  the 
upright  handle  at  the  back  of  the  mould.  A  sound  ingot  may  be  ob- 
tained by  the  use  of  this  simple  little  apparatus  in  a  very  few  minutes. 

Fig.  20  represents  an  improved  form  of  the  preceding  melting  ar- 
rangement. It  differs  in  that  the  two  parts  of  the  ingot-mould  slide 
on  each  other  to  enable  ingots  of  any  width  to  be  cast,  and  the  blow- 
pipe is  part  of  the  rocking  stand.  The  bellows  is  connected  to  the 
upper  tube  and  the  gas  to  the  lower  by  the  usual  means  of  india-rubber 
tubing. 


32 


THE  MECHANICAL   LABORATORY. 


Fig.  20. 


Contrivances  of  this  kind  are,  however,  not  applicable  to  melting 
operations  involving  quantities  exceeding  one  ounce.     In  such  cases  it 

is  better  to  employ  a  crucible  and 
any  stove  or  furnace  in  which  the 
temperature  can  be  raised  suf- 
ficiently. This  may  be  accom- 
plished in  an  ordinary  cooking- 
stove,  a  blacksmith's  forge,  or  a 
small  fire-clay  furnace  by  the  use 
of  anthracite  coal,  coke,  or  char- 
coal. 

By  far  the  most  convenient, 
compact,  and  effective  furnace  for 
melting  from  one  to  ten  ounces  of 
gold  which  has  ever  been  used  is 
the  crucible  furnace  (Fig.  21)  in- 
vented by  Mr.  Fletcher,  which  can 
be  obtained  at  the  dental  depots.  It 
is  perfectly  adapted  to  the  wants  of 
-'-iCMv^^— ^  _       ^^  the  mechanical  dentist.     It  is  com- 

posed of  a  substance  resembling- 
fire-clay,  but  much  lighter  in  weight,  and  said  to  possess  only  one-tenth 
its  conducting  power  for  heat.     The  furnace  consists  of  a  simple  pot  for 


Fig.  21. 


holding  the  crucible,  with  a  lid  and  a  blowpipe,  all  mounted  on  a  suit- 
able cast-iron  base.  The  casing  holds  the  heat  so  perfectly  that  the 
most  refractory  substances  can  be  fused  with  ease  by  the  use  of  a  common 
foot-blower.  The  power  which  can  be  obtained  is  far  beyond  what  is 
required  for  most  purposes,  and  is  limited  only  by  the  fusibility  of  the 
crucible  and  casing.  The  graphite  crucible  made  especially  for  the 
Fletcher  furnace  will  hold  about  ten  ounces  of  gold.  An  ordinary  gas- 
supply  pipe  of  ^-  or  |-inch  diameter  will  work  it  efficiently.  It  re- 
quires a  much  smaller  supply  of  gas  than  any  other  furnace  known  : 
about  ten  cubic  feet  per  hour  is  sufficient  for  most  purposes.  A  gaso- 
line generator  has  been  devised  by  which  these  furnaces  can  be  satisfac- 
torily used  when  ordinary  illuminating  gas  is  not  attainable.  Fig.  22 
shows  the  generator  attached  to  the  furnace  with  foot-blower  complete. 
The  blast  is  obtained  by  means  of  a  foot-blower  connected  with  the 
blowpipe  by  a  flexible  rubber  tube.    The  reservoir  of  the  upper  portion, 


PROCESS  OF  MELTING   GOLD. 


33 


Fig.  22. 


which  holds  the  air,  is,  when  the  bellows  is  not  in  operation,  merely 
a  disk  of  thick  coffer-dam  rubber,  which  expands  under  the  pressure 

of  the  air  while  the  bellows  is  in 
motion,  and  thus  affords  a  very 
compact,  ])ovverfuI,  and  effective 
arrangement.  If  the  rubber  disk 
is  distended  until  forced  against  the 
net,  as  shown  by  Fig.  23,  the  pres- 
sure can  be  increased  to  almost  any 
extent  desired.  It  will  give,  if  re- 
quired, a  heavy  and  continuous  blast 
through  a  pipe  of  a  quarter-inch  bore. 
In  size  the  furnace  is  but  4 
inches  in  diameter  by  3  in  height. 
From  six  to  eight  ounces  of  gold 
require  from  seven  to  twelve  min- 
utes for  perfect  fusion,  the  time  de- 
pending on  the  gas-supply  and  the 
pressure  of  air  from  the  blower. 

In    melting   any  large    amount 
of  gold,   particularly   if  the   melt- 

FiG.  23. 


ing  operation  is  performed  in  an  ordinary  coal-stove,  there  is  always 
danger  of  loss  by  the  escape  of  the  precious  metal  through  some  defect 
in  the  bottom  or  sides  of  the  crucible,  when  its  recovery  from  amongst 
the  fuel  and  ashes  of  the  stove  is  almost  impossible  ;  but  should  such  an 
accident  occur  when  using  the  Fletcher  furnace,  the  complete  recovery 
of  the  gold  or  silver  would  not  be  attended  with  the  least  difficulty. 
A  modification  of  the  apparatus  has  been  made,  adapting  it  to  the 
use  of  refined  petroleum  instead  of  gas  as  a  fuel  (Fig.  24).  Thus  im- 
proved, it  is  said  to  be  in  no  way  inferior  in  efficiency  to  the  gas-furnace. 
The  burner  of  this  furnace  is  constructed  upon  the  principle  of  an 
atomizer,  which,  of  course,  dispenses  with  a  wick  ;  it  is  furnished  wdth  a 
device  for  regulating  the  supply  of  oil  which  is  operated  by  the  milled  nut 
A  shown  on  the  top  of  the  reservoir  in  the  cut,  and  for  the  supply  of  an 
annular  jet  of  air,  which  is  regulated  by  turning  the  sleeve  (B).  This 
burner  is  so  arranged  that  in  case  any  obstruction  should  occur  it  can  be 


34 


THE  MECHANICAL  LABORATORY. 


taken  apart  and  cleaned  by  separating  the  burner  from  the  reservoir, 
which  is  accomplished  by  loosening  the  small  screws,  drawing  out  the 
oil-tube,  taking  off  the  sleeve  B,  and  removing  the  inside  tube. 


Fig.  24. 


Fig.  25. 


These  furnaces  are  so  constructed  that  they  may  be  used  for  either 
gas  or  petroleum,  the  lamp  being  fitted  for  adjustment  in  place  of  the 
gas-burner,  so  that  the  same  apparatus  may  be  used  for  either.  The 
blast  is  obtained  by  means  of  the  foot-blower,  which  is  connected  with 
the  furnace  by  the  india-rubber  tubing,  as  seen  in  the  illustration  (Fig. 
23). 

An  injector  gas-furnace  has  also  been  perfected  by  Mr.  Fletcher, 

which  seems  to  be  well  adapted  to 
the  wants  of  the  dentist  or  metal- 
lurgist (Fig.  26),  and  it  is  claimed 
that  its  power  and  speed  of  work- 
ing are  practically  without  limit, 
depending  only  upon  the  gas-  and 
air-supply. 

With  a  half-inch  gas-pipe  and 
the  small  foot-blower  (see  Fig.  23) 
this  furnace  will  melt  a  crucible 
full  of  cast-iron  scraps  in  ten  min- 
utes. The  supply  of  gas  required 
is  exceedingly  small.  Allowing 
five  cubic  feet  of  gas  for  heating  up^  it  consumes  about  four  feet  of  gas 
for  every  pound  of  metal  melted.  It  is  very  simple  in  construction, 
and  consists  of  two  parts — an  upper  portion,  which  forms  the  cover,  and 
a  lower  part,  which  holds  the  crucible  while  in  operation. 

The  Downie  crucible  furnace  (Fig.  26)  is  one  of  the  latest  devices  espe- 
cially designed  for  melting  metals,  such  as  gold  and  silver,  making  alloys 
for  amalgam,  experimental  work,  etc.  It  is  also  very  useful  in  brazing, 
soldering,  heating  up  bridge-cases  or  metal  plates  to  solder,  etc.  It  has 
two  removable  rings  of  different  widths,  which  set  on  above  the  flaring 
base  to  carry  the  heat  up  around  the  crucible,  the  wide  or  narrow  ring 
being  used,  according  to  the  size  of  the  crucible,  or  both  rings  may  be 
put  on  at  the  same  time.  It  also  has  a  conical-shaped  top  which  can  be 
set  on  above  the  rings  to  confine  the  heat  when  it  is  desired  to  fuse  any 
substance  requiring  a  high  temperature.  This  furnace  can  be  used  for 
baking  continuous-gum  or  any  otiier  por<'elain  work. 


CRUCIBLES. 
Fig.  26. 


35 


Crucibles.— The  terra  "  crucible  "  was  originally  applied  to  a  chem- 
ist's melting-pot,  made  of  earthenware  or  other  material,  and  so  called 
from  the  superstitious  habit  of  the  alchemists  of  marking  such  ves- 
sels with  the  sign  of  the  cross.  The  term  is  now  generally  understood 
as  designating  vessels  in  which  metals  are  melted  at  high  tempera- 
tures. 

A  crucible  should  possess  the  power  of  resisting  high  temperatures 
without  fusing  or  softening.  It  should  also  be  capable  of  retaining  suf- 
ficient strength  when  hot  to  prevent  its  crumbling  or  breaking  when 
grasped  with  the  tongs.  Lastly,  it  should  not  crack  either  in  heating  or 
cooling. 

For  the  purpose  of  melting  metals  crucibles  are  made  of  clay  with 
admixture  of  silica,  burnt  clay,  graphite,  or  other  infusible  material. 
For  use  in  the  dental  laboratory  graphite  crucibles,  which  can  be 
obtained  at  the  dental  depots,  will  be  found  to  answer  every  purpose  : 
they  are  thoroughly  reliable  in  strength  and  durability.  They  range  in 
size  from  2  to  4  inches  high,  and  are  specially  adapted  for  use  in  the 
Fletcher  gas-furnaces. 

When  the  quantity  of  metal  to  be  melted  is  very  small — say,  a  half- 
ounce  of  gold — the  smallest-sized  Hessian  crucible  may  be  used  in  the 
small  Fletcher,  apparatus. 

Before  melting  any  considerable  quantity  of  gold  the  crucible  should 
be  tested,  particularly  if  the  melting  operation  is  to  be  performed  in  an 
ordinary  coal-stove,  where  a  defective  crucible  might  be  the  means  of  a 
considerable  loss.  A  small  amount  of  borax  should  be  placed  in  the 
vessel,  which  should  then  be  exposed  to  a  high  temperature.     Should  it 


36 


THE  MECHANICAL  LABORATORY. 


Fig.  27. 


not  be  perfect,  the  borax  glass  will  run  through  and  glaze  the  surface  on 
the  outside.  If  the  crucible  is  found  to  be  impervious,  it  should  be  so 
inverted  while  yet  hot  that  the  borax  glass  may  cover  the  surface  of  the 
lip  or  groove  out  of  which  the  melted  metal  is  to  be  poured.  This 
facilitates  the  pouring  and  prevents  any  portion  of  the  metal  from 
adhering  to  the  side  of  the  crucible. 

Ingot-moulds  are  constructed  of  various  substances.  For  the  recep- 
tion of  platinum  melted  by  the  oxyhydrogen  blowpipe  they  are  formed 

of  lime  or  coke ;  for  gold  and  sil- 
ver they  are  commonly  made  of 
cast  iron,  about  2  inches  square, 
and  from  an  ^  to  y^  of  an  inch 
thick  (Fig.  27),  with  slightly  con- 
cave inner  surfaces,  as  the  shrink- 
age of  the  ingot  is  greatest  in  the 
centre.  Ingot-moulds  formed  of 
soapstone  are  also  employed,  but 
they  are  not  superior  to  those  made 
of  cast  iron.  Before  pouring  the 
ingot-mould  should  be  heated,  and 
when  made  of  cast  iron  it  sliould 
be  held  over  a  gas-jet  or  oil-flame 
until  its  inner  surface  is  thor- 
oughly coated  with  carbon  :  this 
at  once  prevents  the  possible  con- 
tamination of  the  gold  by  contact 
with  the  iron,  and  the  carbon  layer, 
being  a  good  non-conductor,  pro- 
tects the  melted  metal  at  the  moment  of  pouring  from  too  rapid  cooling, 
which  otherwise  might  be  the  cause  of  a  defective  ingot. 

The  ingot  of  gold  or  silver  should  be  as  nearly  rectangular  as  pos- 
sible (Fig.  28),  and  the  operation  of  pouring  the  melted  metal  from  the 
crucible  into  the  ingot-mould  cannot  be  considered  as  successful  unless 
this  result  has  been  attained.  The  experienced  workman  holds  the 
ingot-mould,  which  should  be  provided  with  a  suitable  handle,  with  the 
left  hand,  while  with  the  right  he  removes  the  crucible  from  the  furnace 


Fig.  28. 


Fig.  29. 


and  quickly  carries  it  to  the  ingot-mould,  which  he  slightly  tilts  so  that 
the  melted  metal  may  first  strike  the  side  of  the  mould ;  but  he  quickly 
brings  the  mould  to  a  level  before  the  last  of  the  fused  metal  leaves  the 
crucible,  and  thus  avoids  the  danger  of  confining  air  at  the  deepest  part 


ROLLING  MACHINE. 


37 


Fig.  30. 


of  the  ingot-mould,  which  would  cause  the  ingot  to  assume  an  irregular 
shape  (Fig.  29). 

The  necessity  for  heating  the  ingot-mould  just  before  it  is  to  receive 
the  melted  metal  becomes  apparent  when  we  remember  that  gold  fuses 
at  2016°  F.,  while  the  iron  ingot-mould 
at  the  temperature  of  the  atmosphere  would 
be  about  70°  F.,  and  when  the  amount  of 
gold  or  silver  to  be  melted  is  but  two  or 
three  ounces,  the  ingot-mould,  weighing  in 
the  neighborhood  of  twelve  ounces,  would 
abstract  so  much  heat  from  the  metal  as  to 
cause  it  to  become  solid  before  it  reaches 
the  lower  part  of  the  mould,  and  the 
result  would  be  an  ingot  triangular  in 
shape  (Fig.  30),  which  could  only  be  rolled  at  a  disadvantage  and  loss. 

Rolling  or  laminating  in  the  dental  laboratory  is  accomplished  by 
repeatedly  passing  the  metallic  ingot  between  cylindrical  steel  rollers 

Fig.  31. 


from  three  to  four  inches  in  width.     These  are  so  arranged  that  by 
means  of  screws  they  are  capable  of  being  brought  closer  together  every 


38 


THE  MECHANICAL  LABORATORY. 


time  the  gold  is  passed  through.  (See  Fig.  31.)  The  proper  degree  of 
attenuation  is  determined  by  the  gauge-plate  (Fig.  32).  After  the  ingot 
has  been  passed  through  the  rolling-mill  a  number  of  times  it  cannot  be 
carried  through  in  an  opposite  direction  in  order  to  increase  its  width 
without  first  carefully  annealing  it.  This  is  done  by  laying  the  gold 
upon  a  large  piece  of  charcoal  and  directing  the  flame  of  the  blowpipe 
upon  it  until  it  becomes  red  hot.  Failure  to  observe  this  precaution 
will  invariably  result  in  serious  damage  to  the  ingot  by  splitting. 


Wire  is  made  by  means  of  the  draw-plate,  which  is  formed  of  an 
oblong  piece  of  hardened  steel  provided  with  a  number  of  gradually 
diminishing  holes   enlarged   on  the   side   the  metal  enters    (Fig.   33). 


Fig.  33. 

20      19      18      17     16      15      14      13      12 
•     •••••••• 

11 

• 

10       9876         54         3 

1 

• 

*  '  *  *  *^^  *  *  * 

GARANTIE 

• 

The  metal  to  be  drawn  through  may  be  prepared  in  a  cylindrical 
shape  by  melting  and  pouring  into  an  ingot-mould  provided  with  a 
chamber  for  the  purpose  (some  ingot-moulds  are  so  constructed).  The 
end  of  the  rod  should  be  filed  so  as  to  readily  enter  the  draw-plate, 
which  must  be  firmly  screwed  in  a  vice.  The  metal  is  then,  by  means 
of  strong  pliers,  drawn  through  the  different  holes  of  the  draw-plate 
consecutively  until  the  desired  size  is  reached.  As  the  work  progresses 
the  wire  will  require  frequent  annealing,  and  to  facilitate  its  passage 
through  the  draw-plate  it  must  be  kept  well  oiled. 


SOLDERING  APPARATUS  AND  ACCESSORIES.  39 

Half-round,  square,  and  triangular  wire  is  drawn  in  the  same  manner, 
except  that  the  holes  in  the  draw-plate  are  made  of  these  respective 
shapes,  instead  of  being  made  round. 

Soldering  Apparatus  and  Accessories. — Soldering  must  also,  to  a 
certain  extent,  be  regarded  as  coming  under  the  general  head  of  melting 
operations,  since  it  refers  to  the  union  of  two  or  more  pieces  of  metal  by 
means  of  a  more  fusible  alloy.  The  conditions  of  successful  soldering 
are — (1)  contact  of  the  two  pieces  to  be  united  ;  (2)  a  clean  metallic  sur- 
face over  which  the  solder  is  to  flow  ;  (3)  a  freely-flowing  solder ;  (4) 
proper  amount  and  distribution  of  heat. 

Contact  of  the  pieces  to  be  united  is  of  the  greatest  importance.'  If, 
for  example,  the  object  to  be  soldered  be  an  artiflcial  denture,  it  is  indis- 
pensable that  the  backings  be  quite  or  very  nearly  in  contact  with  the 
plate,  and  if  gum  teeth  be  used  that  each  backing  touch  its  neighbor. 
This  is  not  difficult  to  accomplish  if  the  teeth  have  been  carefully  and 
accurately  fitted  to  the  plate  and  to  each  other.  If,  however,  any  defects 
of  this  character  are  found  to  exist  after  the  teeth  have  been  invested, 
they  should  be  remedied  by  filling  such  spaces  or  crevices  with  small 
pieces  of  gold  or  silver,  as  the  case  may  be,  thus  rendering  the  continuity 
of  the  parts  complete.  By  the  observance  of  this  precaution  much  of 
the  vexation  in  soldering  experienced  by  beginners  may  be  avoided,  and 
when  the  other  conditions  named  have  been  observed  the  operation 
becomes  exceedingly  simple. 

Solder  runs  freely  by  the  force  of  capillary  attraction  between  two 
closely-fitting  surfaces,  just  as  water  will  be  drawn  against  gravity 
between  two  panes  of  glass  in  close  contact.  In  soldering  artificial 
dentures  which  have  been  carefully  arranged  with  reference  to  contact  of 
all  the  parts  to  be  united,  it  is  quite  possible  to  complete  the  operation  of 
soldering  without  using  the  blowpipe  at  all,  by  merely  heating  the  whole 
case  to  the  fusing-point  of  the  solder  in  a  charcoal  furnace  with  a  good 
draft.  The  difficulties  of  soldering  are  mainly  due  to  a  violation  of  one 
or  more  of  the  rules  herein  given. 

Cleanliness  should  always  be  strictly  observed  in  soldering  operations. 
The  parts  to  be  united  should  present  bright  and  clean  surfaces. 
Darkening  or  oxidation  will  always  occur  when  gold  or  silver  the  purity 
of  which  has  been  reduced  by  alloying  is  heated  to  redness.  A  weak 
solution  of  sulphuric  acid  and  water,  slightly  heated,  will  quickly  remove 
discoloration  resulting  from  this  cause,  or  the  borax  employed  as  a  flux 
in  soldering  operations  will  effect  the  same  result  by  dissolving  the  oxide 
which  forms  on  the  surface,  while  it  also  protects  it  from  further 
oxidation  by  excluding  the  oxygen  of  the  atmosphere. 

Where  broad  surfaces  are  to  be  soldered  together — as,  for  instance,  in 
the  construction  of  the  lower  dentures,  where,  in  order  to  get  sufficient 
thickness,  two  thin  plates  are  swaged  separately  and  then  united  by 
soldering — it  is  even  better,  in  addition  to  the  pickling  process,  to  thor- 
oughly scrape  the  surfaces  to  be  united,  so  as  to  ensure  the  flowing  of  the 
solder  between  the  two  plates.  All  surfaces  to  be  soldered  should  receive 
a  coating  of  borax  before  the  heat  is  applied. 

Borax,  which  is  so  indispensable  in  soldering  operations,  has  the 
chemical  composition  of  Na2B4O„10H2O ;  it  is  a  pyroborate  of  sodium, 
and  occurs  in  the  waters  of  certain  lakes  in  Thibet,  Persia,  and  Call- 


40 


THE  MECHANICAL  LABORATORY. 


fornia.  It  crystallizes  in  six-sided  prisms,  which  effloresce  in  dry  air ;  it 
dissolves  in  20  parts  of  cold  and  6  of  boiling  water.  On  exposure  to 
heat  the  10  molecules  of  water  of  crystallization  are  expelled  ;  at  a  higher 
temperature  the  salt  fuses  and  becomes  glass,  in  which  state  it  has  the 
power  of  dissolving  metallic  oxides ;  and  it  is  this  quality  which  makes 
it  such  an  admirable  flux  in  soldering  and  melting  operations.  It  must, 
however,  be  kept  scrupulously  clean,  and  especially  free  from  accidental 
admixture  with  plaster  of  Paris.  Recently  fluxes  composed  principally 
of  borax,  prepared  and  used  in  the  form  of  dry  powder,  have  been  intro- 
duced, but  they  are  in  no  respect  superior  to  the  old  way  of  rubbing  up 
the  borax  on  a  piece  of  ground  glass  with  perfectly  clean  water  until  it 
assumes  the  consistence  of  cream,  when  it  is  applied  to  the  surfaces  to  be 
soldered  with  camel's-hair  brush.  A  large  crystal  of  borax  should  be 
selected  for  this  purpose  and  given  several  coats  of  shellac  varnish  to 
prevent  efflorescence.  Powdered  glass  of  borax  is  sometimes  a  useful  and 
convenient  adjunct  when  it  is  necessary  to  apply  more  borax  to  a  hot 
surface,  as  in  that  form  it  may  be  dropped  M'ith  the  fingers  upon  any 
desired  point  of  the  heated  denture  without  danger  to  the  porcelain  teeth. 
Fig.  34  shows  a  convenient  and  compact  arrangement  designed 
by  Dr.  H.  H.  Keith  of  St.  Louis,  Missouri,  in  which  may  be  kept 
the  borax  crystal,  the  different  grades  of  solder,  tweezers  for  hand- 
ling email  pieces  of  solder,  and  camel's-hair  brushes.     It  is  provided 

Fig.  34. 


with  a  ground-glass  plate,  depressed  in  the  centre  (A),  for  rubbing  the 
borax  with  water  to  the  consistence  suitable  for  application  to  the  metallic 
surfaces  to  be  soldered.  When  not  in  use  it  may  be  closed  with  the  lid 
B,  which  protects  the  borax  from  contamination  with  plaster  or  other 
deleterious  substances.  This  neat  little  accessory  of  the  soldering  table 
is  made  of  walnut  wood  and  is  as  ornamental  as  it  is  useful. 

The  soMermg  table  is  an  indispensable  piece  of  laboratory  furniture, 
because  it  enables  the  operator  to  sit  while  soldering,  thus  affording  a 
rest  for  the  right  arm  while  the  hand  guides  the  blowpipe,  and  it  sup- 
plies a  convenient  place  for  charcoal  "  supports "  and  other  soldering 
accessories.  It  may  be  arranged  in  the  form  of  a  mechanical  blowpipe, 
such  as  were  formerly  manufactured  by  the  late  Mr.  Bishop  of  Phila- 


SOLDERING  APPARATUS  AND  ACCESSORIES. 


41 


Fig.  35. 


delphia,  and  shown  by  the  accompanying  cut.  (See  Fig.  35.)  They  are 
provided  with  a  pump  (2)  and  an  air-chamber  (1) ;  the  blowpipe  (3)  is 
attached  to  the  air-chamber  by 
a  ball-and-socket  joint,  which  is 
readily  moved  in  any  direction, 
and,  being  self-retentive,  leaves 
the  right  hand  free,  which  is 
often  a  great  convenience  when 
it  is  necessary  to  add  more  solder 
or  borax  or  to  guide  the  solder 
when  its  free  flowing  is  retarded 
by  oxidation  of  the  surfaces. 
The  air-chamber  may  be  pro- 
vided with  a  plain  nozzle,  as 
shown  by  (3)  of  the  illustration, 
for  the  attachment  of  rubber 
tubing  by  which  any  one  of  the 
new  forms  of  hand  blowpipes 
may  be  substituted  for  the  self- 
retentive  ball-and-socket  pipe. 
(See  Figs.  46,  47,  48,  showing  of  automatic  blowpipes  for  crown-  and 
bridge-work  and  general  soldering  purposes.) 

Fig.  36. 


The  Burgess  blowpipe  illustrated  in  Fig.  36  is  constructed  on  the 
same  general  principles  as  the  Bishop.    It  is  not  attached  to  a  table,  but 


42 


THE  MECHANICAL  LABORATORY. 


may  be  used  as  an  attachment  to  the  soldering  table.    It  is  a  simple  and 
efficient  apparatus  for  maintaining  a  continuous  supply  of  air  in  solder- 


FiG.  37. 


Fig.  39. 


Fig.  38. 


ing,  giving  a  steadier  and  stronger 
blast  than  can  be  obtained  by  the 
use  of  the  ordinary  blowpipe.  A 
pressure  of  from  two  to  twelve 
pounds  is  produced  at  the  will  of 
the  operator  by  accelerating  the 
motion  of  the  foot.  The  machine 
w^eighs  12  pounds,  and  measures 
22  inches  in  height.  The  pump- 
cylinder  is  2|  inches  in  diameter, 
with  3-inch  stroke.  The  internal 
mechanism  is  clearly  illustrated  in 
Fig.  36. 

Mr.  Fletcher  has  devised  a  foot- 
blower,  show^n  in  Figs.  37,  38, 
which  may  be  used  with  any  form 
of  blowpipe.  The  reservoir  of  the 
upper  portion,  which  holds  the  air,  is, 
when  the  bellows  is  not  in  opera- 
tion, merely  a  disk  of  thick  coffer-dam  rubber,  which  expands  under 


Mouth  blowpipes  (brass). 


THE  MOUTH  BLOWPIPE. 


43 


the  pressure  of  the  air  while  the  bellows  is  in  motion,  and  thus  affords 
a  compact,  powerful,  and  effective  arrangement.  The  step  for  the  foot 
is  very  low,  and  the  blower  may  be  used  Avith  ease  whether  the  operator 
is  standing  or  seated.  The  pressure  is  steady  and  equal,  and  if  the 
rubber  disk  is  distended  until  forced  against  the  net,  it  can  be  increased 
to  almost  any  extent  desired,  and  will  give,  if  required,  a  heavy  and 
continuous  blast  through  a  pipe   of  a  quarter-inch  clear  bore. 

The  mouth  blowpipe  is  an  instrument  which  has  long  been  used  by 
workers  in  metals  for  the  purpose  of  soldering  together  small  pieces 
of  metal  and  for  melting  and  reducing  purposes  generally.  The  ordi- 
nary form  (Fig.  39  J.)  consists  of  a  conical  brass  tube,  from  200  to  240  mm. 
long,  curved  at  the  narrower  end  to  nearly  a  right  angle,  so  that  the 
flame  may  be  conveniently  directed  upon  the  piece  of  metal  to  be  sol- 
dered or  melted,  as  the  case  may  be,  which  is  held  upon  some  suitable 
support,  such  as  a  piece  of  charcoal,  coke,  or  pumice-stone.  When  the 
blowpipe  is  used  in  its  simplest  form,  by  the  mouth,  the  large  end  of  the 
instrument  is  held  between  the  lips  and  the  small  end  toward  the  flame. 
The  blast  should  not  be  sustained  by  the  respiratory  organs,  but,  in 
order  that  an  unbroken  current  may  be  kept  up,  the  mouth  should  be 
filled  with  air,  to  be  forced  through  the  blowpipe  by  the  muscles  of  the 
cheeks.  While  these  are  forcing  the  air  through  the  blowpipe  the  con- 
nection between  the  chest  and  the  cavity  of  the  mouth  should  be  closed 
by  the  palate,  which  thus  performs  the  part  of  a  valve.  The  beginner 
is  liable  to  fall  into  the  error  of  not  closing  the  connection  between  the 
chest  and  the  mouth  at  the  proper  instant,  and  of  obtaining  the  force 
necessary  to  propel  the  air  through  the  blowpipe  from  the  lungs.  That 
this  manner  of  using  the  instrument  may  injure  the  organs  of  respiration 
cannot  for  a  moment  be  doubted,  and  the  operator  should  early  acquire 
the  proper  method  above  described.  To  avoid  tiring  the  muscles  of  the 
lips  by  long-continued  blowing  the  trumpet  mouth-piece  has  been  rec- 

FiG.  40. 


ommended,  and  is  shown  in  the  annexed  cut  (Fig.  40).  This  is  merely 
pressed  against  the  open  mouth,  and  an  uninterrupted  blast  may  be  kept 
up  for  a  long  time  without  causing  the  least  fatigue  of  the  orbicularis 
oris,  since,  when  the  trumpet  mouth-piece  is  used,  that  muscle  takes  but 
a  passive  part  in  the  operation.  This  trumpet-piece,  however,  should 
be  so  curved  as  to  correspond  with  the  shape  of  the  mouth,  otherwise  it 
will  require  to  be  pressed  very  forcibly  against  the  lips  in  order  to  pre- 
vent the  escape  of  air. 

The  blowpipe  should  be  constructed  of  either  brass  or  German  silver, 


44 


THE  MECHANICAL  LABORATORY. 


as  these  alloys  are  but  poor  conductors  of  heat.      Silver  is  not  well 

Fig.  41. 


Fig.  42. 


m 


Fig.  43. 


suited  for  the  purpose,  because  it  transmits  temperatures  so  readily  that 
it  soon  becomes  too  hot  for  the  fingers. 

A  long-continued  and  steady  flame  maintained  by  the  mouth  blow- 
pipe is  apt  to  cause  disturb- 
ances in  the  flame  from  the  col- 
lection of  moisture  in  the  tube, 
which  is  liable  to  be  expelled 
by  the  pressure  of  the  air.  To 
avoid  this  a  hollow  chamber  is 
constructed  about  midway  in 
the  instrument  (Figs.  39  jB,  and 
41).  The  length  of  the  blowpipe 
should  be  adapted  to  the  eye  of 
the  operator,  so  that  the  object 
upon  which  the  flame  is  directed 
may  be  distinctly  seen. 

Improvements  in  these  in- 
struments (Figs.  41-45)  have 
been  made  by  Mr.  Thomas 
Fletcher,  F.  C.  S.,  of  Warring- 
ton, England,  by  which  tem- 
peratures beyond  those  which 
can  be  produced  by  the  ordinary 
form  of  blowpipes  are  attainable. 
They  not  only  give  temperatures 
never  approached  by  the  old 
blowpipes,  but  are  in  every  respect  more  convenient,  easier  to  use,  and 
better  adapted  for  every  class  of  work.  With  the  same  amount  of 
blowing  as  with  the  common  form  these  blowpipes  will  do  nearly  double 
the  work  :  if  high  temperatures  are  not  required,  the  labor  of  blowing  is 
reduced  in  proportion.    The  chief  improvement  consists  in  coiling  the  air- 


Fig.  44. 


Fig.  45. 


THE  AUTOMATON  BLOWPIPE. 


45 


tube  into  a  light  spiral  over  the  point  of  the  jet.  This  coil  takes  up  the 
heat  which  would  otherwise  be  wasted,  and  utilizes  it  by  heating  the  air 
in  its  passage.  The  author  has  found  this  form  of  mouth  blowpipe  to 
be  well  adapted  for  fine  analytical  operations  by  cupellation,  as  well  as 
for  all  the  uses  of  the  dental  laboratory. 

The  "  automaton  blowpipe,"  a  somewhat  recent  improvement  of  Mr. 
Fletcher's  intended  for  general  laboratory  use,  and  much  employed  by 

Fig.  46. 


experts  in  crown-  and  bridge-work  where  gas  is  available,  has  quite 
superseded  the  mouth  blowpipe  in  all  delicate  soldering  operations.  The 
blast  may  be  supplied  by  either  the  Bishop,  Burgess,  or  Fletcher  foot- 
blower.  The  supply  of  gas  and  air  is  controlled  by  a  longitudinal 
movement  of  the  tube,  worked  by  a  spring  under  slight  pressure  of  the 
hand  when  it  is  held  as  shown  in  the  illustration  (Fig.  46).     This  is 

Fig.  47. 


sufficient  to  give  either  a  pointed  jet  or  a  full-sized  flame  at  will.  The 
gas-passage  does  not  close  entirely,  but  allows  of  the  escape  of  enough 
gas  to  prevent  the  flame  from  going  out  when  the  blowpipe  is  not  in 
use,  and  it  may  be  hung  up  by  the  ring  which  is  attached  to  it  when  it 
is  desirable  to  get  it  out  of  the  hand. 

Dr.  Geo.  W.  Mellott  has  devised  a  blowpipe  especially  for  use  in 
crown-  and  bridge-work,  which  is  in  many  respects  similar  to  the  pre- 
ceding.    The  gas  is  supplied  through  a  valved  tube  (Fig.  47)  by  con- 


46 


THE  MECHANICAL  LABORATORY. 

Fig.  48.  Fig.  49. 


n  n 


necting  it  with  rubber  tubing  to  a  gas- 
bracket. The  spring  valve  which  regu- 
lates the  supply  of  gas  may  be  set  by 
means  of  a  thumb-screw  and  jam-nut  to 
a  flame  of  any  desired  size.  When  used 
as  a  hand  blowpipe  the  best  way  to  hold 
it  is  with  the  third  finger  through  the 
ring,  as  shown  in  Fig.  48.  It  can  also 
be  used  with  the  foot-bellows  when  a  more 
powerful  blast  is  required,  or  with  nitrous 
oxide  to  procure  an  oxyhydrogen  flame. 

The  blowpipe  designed  by  Dr.  F.  H. 
Lee  is  shown  in  the  annexed  illustration 
(Fig,  49).  It  is  provided  with  a  mouth- 
piece with  rubber  tubing,  so  that  it  can 
be  operated  by  the  mouth,  or,  by  removing 
that  attachment,  with  the  foot-blower.  The 
flame  is  controlled  by  the  spring  lever  so 
accurately  that  a  wire  flame  can  be  directed 
upon  a  particular  spot.  Releasing  the 
lever  shuts  off  the  gas-supply,  allowing 
only  enough  to  escape  to  keep  the  flame 
lighted  for  future  use. 

Where  gas  is  not  available  a  simple  and 
perfectly  safe  blowpipe,  made  expressly 
for  use  with  gasoline  gas,  has  been  devised 
which  possesses  a  power  and  efficiency 
fully  equal  to  that  obtained  from  coal- 
gas.  As  shown  in  Fig.  50,  it  is  provided 
with  a  generator  (A)  which  requires  a 
supply  of  air  under  pressure,  and  is  there- 
fore operated  in  connected  with  a  foot- 
bellows  (B).  To  charge  the  generator 
pour  gasoline  in  the  funnel-cock  until 
it  overflows  at  the  small  tap  in  the 
side  of  the  generator  near  the  bottom  ;  then  close  the  funnel-cock  and 


Lee  blowpipe. 


VARYING    QUALITIES  OF  GASOLINE. 


47 


first 


Fig.  50. 


also  the  overflow  tap.  After  charging  the  generator  connect  the  foot- 
blower  to  the  "  tee  "  on  the  end  of  the  generator  by  a  two-foot  piece  of 
the  large  rubber  tubing  of  ^^-inch  diameter.  Cut  from  the  large  tubing 
a  3-inch  piece  and  attach  to  the  other  branch  of  the  "  tee,"  havin-  ^^^+ 
inserted  the  large  end  of  the 
brass  reducer  in  one  end  of 
the  tubing.  Then  connect 
the  reducer  and  air-pipe  C  to 
the  blowpipe  D  by  means  of 
the  small  tubing  C.  The  re- 
mainder of  the  large  tubing 
is  then  attached  to  the  cock 
on  the  dome  of  the  generator 
and  to  the  large  end  of  the 
hand-piece  of  the  blowpipe. 

To  operate  the  blowpipe 
open  the  cock  behind  the 
"  tee,"  and  then  the  cock  on 
the  dome ;  then  operate  the 
blower  slowly  and  ignite  the 
vapor  at  the  blowpipe  nozzle. 
The  quantity  of  vapor  re- 
quired is  adjusted  by  the  tap 
behind  the  "  tee  "  on  the  end 
of  the  generator.  The  size 
of  the  flame  is  controlled  by 
the  thumb-valve  on  the  blow- 
pipe, .shown  in  Fig.  51.  A 
very  light  pressure  of  air  is 
required  to  operate  this  form 
of  blowpipe. 

Different  samples  of  gaso- 
line will  often  be  found  to 
vary  in  quality.  When  a  few 
drops  of  a  good  quality  of 
this  material  are  poured  on 
a  plate,  it  should  evaporate 
quickly  and  completely,  leav- 
ing no  greasy  residue:  74°  to  76°  gasoline,  such  as  is  commonly  used  in 
''vapor  stoves"  for  culinary  purposes,  is  suitable  for  use  in  the  "gasoline 


Fig.  51. 


Gasoline  blowpipe. 


generator  and  blowpipe." 
not  give  as  good  results. 


The  heavier  hydrocarbons  or  naphthas  will 
It  is  important  that  all  the  tubing  used  in 


48 


THE  MECHANICAL  LABORATORY. 


connection  with  this  apparatus  be  kept  in  good  order,  otherwise  its  power 
may  be  greatly  reduced.  If  the  gasoline  is  of  inferior  quality  and  con- 
tains the  heavier  oils,  the  generator  will  not  work  satisfactorily  ;  it  will 
then  require  emptying  and  refilling  with  a  better  quality  of  gasoline.  At 
the  conclusion  of  an  operation  all  taps  on  the  generator  should  be  closed ; 
it  can  then  be  left  for  any  length  of  time  ready  for  instant  use. 


Fig.  52. 


Fig.  53. 


Fig.  54. 


Automatic  blowpipe 

There  are  other  forms  of  automatic  blowpipes  (Figs.  52-54),  which 
are  mounted  on  iron  bases  and  provided  with  a  ball-joint,  so  as  to  be 
self-retentive  and  adjustable  at  the  will  of  the  operator. 

The  hot-blast  blowpipe  devised  by  Mr.  Fletcher,  shown  in  Figs.  54 
and  55,  possesses  a  power  but  little  inferior  to  the  oxyhydrogen  blowpipe. 
It  fuses  pure  gold  Avithout  difficulty,  and  is  therefore  of  great  value  as  a 
soldering  appliance  in  continuous-gum  work,  where  gold  in  its  unalloyed 
state  is  used  as  the  solder.    The  use  of  a  powerful  blowpipe  is  undoubtedly 

a  safer  means  of  soldering  the  teeth  to  the 
plate  in  this  class  of  dentures  than  is  the 
other  plan  of  completing  that  part  of  the 
work  in  the  muffle  of  a  furnace,  for  by  the 
latter  means  the  danger  of  "  etching "  the 
teeth  is  greatly  increased,  as  the  teeth  are 
necessarily  brought  to  the  maximum  tem- 
perature ;  whereas  by  the  use  of  a  blowpipe, 
the  piece  having  first  been  thoroughly  dried 
and  heated  to  a  point  considerably  below  the 
fusing-point  of  gold,  the  flowing  of  the 
solder  is  accomplished  by  concentrating  the 
heat  upon  the  points  to  be  united,  while  the  asbestos  and  plaster  invest- 
ment protects  the  porcelain  teeth  from  a  very  high  degree  of  heat.  In 
this  instrument  the  air-pipe,  as  will  be  seen,  is  coiled  around  the  gas- 
pipe,  and  both  are  heated  by  three  small  Bunsen  burners,  the  gas-supply 
to  which  is  controlled  by  a  separate  stopcock.     The  air-blast  is  obtained 


BLOWPIPE   WORK. 


49 


by  a  foot-blower  connected  with  the  blowpipe  by  means  of  a  flexible 
rubber  tube.     (See  Fig.  55.) 

Wherever  gas  can  be  obtained  it  furnishes  at  once  the  best  and 

Fig.  55. 


Fig.  56. 


Fig.  57. 


Hot-blast  blowpipe. 

most  economical,  as  well  as  safest,  fuel  for  blowpipe  work.  Those 
who  prefer  the  detached  flame  and  simple  form  of 
blowpipe,  which  may  be  used  either  J^y  the  mouth 
or  foot-blower,  to  the  more  recent  compound  appa- 
ratus of  Mr.  Fletcher,  may  readily  construct  a  burner 
which  will  be  found  to  answer  every  requirement  of 
the  laboratory  by  attaching  to  the  base  of  an  ordi- 
nary Bunsen  burner, 
which  may  be  obtained 
at  the  dental  depots 
(see  Fig.  57),  a  piece  of 
brass  tubing  6  inches 
in  length  by  1^  inches 
in  diameter.  Over  the 
top  of  this,  in  order  to 
properly  spread  the 
flame,  a  piece  of  fine 
brass -wire  gauze  is 
fastened  by  means  of 
a  ring  of  sheet  brass  ^ 
of  an  inch  in  width. 
Connection  may  be 
made  with  the  gas- 
bracket in  almost  any 
part  of  the  room  by  means  of  flexible  rubber  tubing. 

Another  form  of  heating  apparatus,  designed  for  soldering  with  the 
oi'dmary  simple  blowpipe  and  for  other  laboratory  uses,  is  represented  in 
Fig.  56.  It  is  known  as  the  "  duplex  burner."  In  addition  to  the  usual 
Bunsen  burner,  a  larger  flame  for  soldering  purposes  can  be  obtained  by 


50  THE  MECHANICAL  LABOBATOBY. 

rotating  the  upper  portion  upon  the  base.  A  small  jet,  when  once 
lighted,  ignites  either  flame,  so  that  it  is  always  ready  for  use.  When 
used,  however,  for  all  kinds  of  soldering  operations,  large  and  small,  this 
burner  is  inferior  to  the  one  previously  described. 

In  villages  and  small  country  places  gas  is  not  always  available,  and 
it  may  therefore  become  necessary  for  the  dentist  to  use  a  soldering  lamp 
burning  alcohol,  kerosene,  or  gasoline.  Of  the  three,  the  latter  is  prob- 
ably preferable  since  the  introduction  of  Mr.  Fletcher's  admirable  gaso- 
line generator  and  blowpipe,  but  this  agent  cannot  be  used  with  safety  in 
an  ordinary  lamp. 

When  either  alcohol  or  kerosene  is  employed,  it  is  of  the  greatest 
importance  that  a  lamp  designed  to  meet  the  practical  requirements, 
and  also  with  a  view  to  safety  be  selected.  The  first  essential  is  to 
have  the  wick  large  enough  to  afford  a  flame  of  sufficient  magnitude  to 
enable  the  operator  to  solder  an  entire  artificial  denture  or  to  fuse  from 
one  to  two  ounces  of  gold.  This  would  require  a  wick  at  least  1^  inches 
in  diameter  and  about  3  inches  long.  Its  connection  with  the  reservoir 
or  body  of  the  lamp,  which  should  have  a  capacity  of  not  less  than  1 
pint,  in  which  the  combustible  fluid  is  contained,  should  not  be  direct  nor 
in  such  close  proximity  that  explosive  gas  would  be  likely  to  form.  The 
"  Franklin  safety  lamp,"  a  cut  of  which  is  annexed  (Fig.  58),  will  be 

Fig.  58. 


S^  I    -/ 


found  to  answer  every  requirement.  It  consists  of  a  reservior  5  mches 
in  diameter  by  2^  inches  deep.  The  wick-holder,  3  inches  long  by  1^ 
inches  in  diameter,  is  connected  with  the  reservoir  by  a  curved  tube  5 
inches  long  by  j\  of  an  inch  in  diameter.  Thus  a  sufficient  quantity 
of  the  burning  fluid  is  supplied  to  the  wick  to  afford  a  constant  flame, 
while  there  is  very  little  danger  of  the  heat  from  the  wick-holder  benig 
conducted  to  the  reservoir.  The  author  has  found  that  most  of  the 
explosions  during  soldering  operations  which  have  come  under  his 
notice  were  due  to  the  case-heater — or  soldering- pan,  as  it  is  more  com- 
monly called— filled  with  live  coals,  being  held  for  a  long  time  so  close 
to  the  lamp  that  inflammable  gases  were  generated  and  ignited  from 
the  wick,  when  an  explosion  of  more  or  less  violence  inevitably  fol- 
lowed. The  Franklin  safety  lamp  is  constructed  upon  correct  princi- 
ples, as  is  also  the  lamp  represented  in  Fig.  59,  but  such  forms  of  lamps 


SUPPOBTS. 


51 


as  are  shown  in  Fig.  60  should  always  be  avoided,  except  for  use  with 
non-explosive  oils. 

Supports. — In  melting  small  quantities  of  gold  or  silver  or  in  solder- 
ing with  the  blowpipe  flame  it  is  necessary  to  perform  these  operations 
upon  a  support  made  of  some  suitable  body,  such  as  charcoal,  coke, 
pumice-stone,  or  asbestos  and  plaster,  charcoal  and  plaster,  etc. 

Well-burned  charcoal  is  especially  suited  for  both  purposes,  as  it  helps 
to  increase  the  heat,  and  in  the  putting  together  of  small  quantities  of 


Fig.  59. 


Fig.  60. 


gold  or  silver  solders  prevents  oxidation  of  the  base  metals  which  are 
added  to  reduce  the  fusing-point  of  the  alloy  and  cause  it  to  flow  freely. 
Charcoal  made  from  the  light  woods,  such  as  pine,  is  best,  because  it  is 
not  so  likely  to  throw  sparks  when  the  flame  is  directed  upon  it  as  are 
the  harder  coals,  such  as  that  made  from  oak ;  and,  being  softer,  it  is 
much  better  adapted  to,  soldering  operations  in  which  it  is  necessary  to 
hold  the  pieces  to  be  united  together  by  means  of  small  nails  or  tacks 
thrust  into  the  support ;  as,  for  instance,  where  a  rim  is  to  be  soldered 
to  a  plate,  the  former  must  be  brought  in  contact  with  the  latter  upon 
the  charcoal,  and  so  held  during  the  preliminary  soldering,  which  con- 
sists of  uniting  the  rim  to  the  plate  with  a  small  piece  of  solder  at  some 
one  point,  after  which  the  accurate  adjustment  of  the  rim  to  the  plate  for 
final  soldering  is  rendered  much  easier. 

A  good  solid  piece  of  charcoal,  sufficiently  large,  should  be  selected, 
and  bound  with  iron  or  copper  wire  to  prevent  its  breaking  into  pieces. 
It  should  then  receive  a  coating  of  plaster,  from  a  quarter  to  a  half  inch 
in  thickness,  on  all  sides  except  the  one  upon  which  the  object  to  be 
soldered  is  to  rest.  This  adds  to  its  strength  and  prevents  the  fingers 
from  being  soiled  in  handling  it.  Good  charcoal,  suitable  for  use  in  the 
dental  laboratory,  cannot,  however,  always  be  found  when  wanted,  and 
it  is  therefore  often  necessary  to  use  some  other  substance  which  may  be 
more  easily  obtained.  Thus  those  living  in  large  cities  may  be  com- 
pelled to  employ  pieces  of  coke  as  support  in  soldering.  Next  to  char- 
coal, coke  is  most  suitable  for  that  purpose.  It  is  more  durable  than 
charcoal,  and  when  such  a  support,  composed  of  one  large  piece  or  even 
several  smaller  pieces,  is  bound  together  with  wire  and  coated  with 
plaster,  it  will  last  a  long  time.  Large  pieces  of  pumice-stone  also 
answer  well  for  the  purpose  of  holding  small  objects  while  the  flame  of 
the  blowpipe  is  directed  upon  them.  Neither  of  these,  however,  is  so 
well  adapted  as  charcoal  for  holders  when  small  quantities  of  metals 
are  to  be  melted,  in  consequence  of  their  greater  porosity  and  hardness, 


52 


THE  MECHANICAL  LABORATORY. 


which  prevent  the  cutting  of  suitable  pits  for  the  reception  of  the 
metal  to  be  fused. 

A  very  good  support  for  soldering  purposes  alone  may  be  formed  by 
filling  a  cup  made  of  sheet  iron  or  copper,  5  inches  in  diameter  by  5 
inches  in  depth,  with  a  mixture  of  asbestos  and  plaster  or  plaster  and 
finely-broken  charcoal.  The  vessel  should  be  supplied  with  a  wooden 
handle,  fastened  in  the  bottom,  for  convenience  in  handling. 

Plattner's  Manual  of  Qualitative  and  Quantitative  Analysis  with  the 
Blowpipe,  p.  15,  gives  a  method  of  artificially  preparing  good  solid  sup- 
ports of  charcoal  which  might  be  found  of  value  in  the  dental  labora- 
tory. It  consists  of  mixing  charcoal-dust  (which  must  not  be  too  finely 
ground)  with  starch  paste.  The  latter  is  prepared  by  combining  1  part 
of  starch  with  6  parts  of  boiling  water.  These  are  stirred  in  an  earthen 
pot  until  all  the  meal  is  converted  into  paste.  This  paste  is  rubbed  in  a 
porcelain  mortar  with  frequent  additions  of  charcoal-dust  until  the  mass 
Ijecomes  too  tough  for  further  admixture,  when  enough  of  the  coal-dust 
is  kneaded  in  with  the  hands  to  render  the  whole  mass  stiif  and  plastic. 
From  this  the  desired  forms  of  supports  can  be  made,  allowed  to  dry 
gradually  and  thoroughly,  and  then  heated  to  redness  in  a  covered  ves- 
sel, so  as  to  char  the  starch  paste.  The  charring  may  be  regarded  as. 
complete  when  the  evolution  of  gases  from  the  mass  ceases  or  when  it 


Fig.  61. 


Fig.  62. 


has  been  heated  to  dull  redness.     Coals  thus  formed  are  of  the  proper 
firmness,  and  ring  like  ordinary  good  charcoal  when  thrown  on  the  table. 
Blocks  formed  of  graphite  and  fire-clay  are  now  often  used  as  sup- 
ports for  holding  objects  to  be  soldered.     These  are  by  no  means  perfect. 


Fig.  64. 


non-conductors,  and  when   used   without  some  protection  to  the  hand 
they  soon  become  so  hot  in  the  operation  of  soldering  that  it  is  impos- 


SOLDERING  BLOCKS. 


53 


sible  to  hold  one  for  any  length  of  time.  To  overcome  this  difficulty, 
however,  a  very  convenient  device  for  holding  the  carbon,  graphite,  or 
other  support  has  been  introduced.     (See  Figs.  61  to  63.) 


Fig.  65. 


Soldering  blocks  have  recently  been  formed  of  asbestos,  and  have 
found  favor  with  many  in  preference  to  the  "  carbon  block  "  for  solder- 


FiG.  66. 


JjVUSBESTOS  BLOCI<i, 
-^■S.W||iT|rD.|vi.C0| 


ing  purposes.     They  are  circular,  depressed  on  each  face,  and  4  inches 
in  diameter. 

The  carbon  cylinder,  made  of  the  same  composition  as  the  carbon 
block,  is  a  new  form  of  support  admirably  adapted  for  soldering  small 
articles,  such  as  gold  crowns,  or  for  blowpipe  assays.  In  size  it  is  1^ 
inches  in  diameter  by  3  inches  in  length  (Fig.  64). 

Amongst  the  more  recently  introduced  forms  of  asbestos  soldering 
and  melting  supports  are  those  shown  in  the  annexed  illustrations. 
Fig.  65  represents  a  combined  soldering,  melting,  and  ingot  block,  6 
inches  long,  2^  inches  wide,  by  ^  an  inch  in  thickness.  Fig.  QQ  shows 
an  asbestos  support  intended  exclusively  for  soldering,  4|^  inches  in 
diameter  by  If  inches  high,  with  concave  top,  and  provided  with  a  con- 
venient holder,  which  also  prevents  the  support  from  being  laid  flat 
upon  the  table  while  hot.  Fig.  67  shows  an  asbestos  soldering  tray 
which  is  particularly  useful  in  soldering  crown-  and  bridge-work.  It 
has  a  raised  rim  set  in  a  brass  box  mounted  on  a  wooden  handle,  the 
end  of  which  is  flat,  so  that  the  appliance  can  be  held  in  the  hand  or 
set  upright  on  the  work-bench.  Four  holes  are  drilled  in  the  bottom 
for  the  reception  of  brass  pins  to  hold  the  Avork  in  place. 

When  the  object  to  be  soldered  is  an  artificial  denture  containing  a 
number  of  teeth,  a  support  that  will  be  found  to  answer  all  requirements 
is  the  hand-furnace,  such  as  is  now  furnished  by  the  dental  depots  (Fig. 


54 


THE  MECHANICAL  LABORATORY. 


Fig.  67. 


68).     It  consists  of  a  funnel-shaped  receptacle  of  sheet  iron,  with  a 
grate  or  perforated  plate  near  the  bottom,  and  a  small  door  on  one  side 

underneath  the  grate  for  the  ad- 
mission of  air.  The  upper  part 
of  the  holder  is  surmounted  by  a 
cone-shaped  top ;  to  the  bottom  is 
attached  an  iron  rod,  six  or  eight 
inches  long,  terminating  in  a  wooden 
handle.  This  apparatus  is  designed 
to  serve  both  the  purpose  of  heat- 
ing the  case  and  as  a  support  or 
holder  during  the  soldering.  For 
the  first  it  is  not  well  suited,  being 
too  small  to  contain  fuel  enough  to 
admit  of  a  thorough  heating  of  the 
invested  denture  ;  but  when  the  ob- 
ject has  been  brought  to  the  proper 
temperature  it  makes  an  admirable 
holder  for  a  set  of  teeth  while  the 
flame  of  the  blowpipe  is  being  di- 
rected upon  it. 

The  best  method  of  "  heating 
up "  a  denture  preparatory  to  sol- 
dering is  to  place  it  on  a  gas-oven, 
such  as  is  employed  in  the  dental 
laboratory  for  general  use  and  for 
heating  flasks  in  packing  rubber 
work,  etc.  (Fig.  69  ).  A  ring  of 
cast  or  sheet  iron,  6  inches  in  diameter  by  2  inches  high,  should  then 

Fig.  68. 


Soldering  furnace. 

be  placed  around  it  for  the  purpose  of  holding  the  charcoal,  which,  in 


"HEATING    UP^^  A  DENTURE. 


55 


pieces  the  size  of  a  hen's  egg,  should  be  built  around  the  outside  of  the 
denture  so  that  it  may  be  uniformly  heated.     The  cone  or  top  of  the 


Fig.  69. 


Fig.  70. 


apparatus  just  described  may  now  be  placed  over  it.     The  gas  is  then 
lighted,  but  the  full  head  should  not  be  turned  on  until  the  moisture  of 


Fig.  71. 


the  investment  has  been  driven  off,  when  it  may  be  gradually  increased 
until    the    piece    is  heated  to    redness.     About  thirty  minutes  will  be 


56 


THE  MECHANICAL   LABORATORY. 


required  to  reach  the  proper  temperature  for  sokleriug,  when  tlie  piece 
may  be  Hfted  from  the  gas-oven  with  suitable  tongs  and  placed  in  the 
hand  furnace.  The  live  coals  used  in  heating  up  should  also  be  placed 
around  the  outside  of  the  investment  to  prevent  the  too  rapid  cooling 
of  the  piece  should  any  delay  in  the  soldering  occur.  When  the  latter 
operation  has  been  satisfactorily  completed,  the  top  may  be  placed 
tightly  on  and  all  access  of  air  excluded,  in  order  that  the  piece  may 
cool  slowly  and  thus  avoid  the  danger  of  cracking  the  teeth. 

The  "  Lewis "  combined  case-heater  and  soldering-cap  (Fig.  71)  is 
a  recently  improved  device  for  drying  out  and  soldering  an  invest- 
ment of  gold  work  without  removing  until  completed.  It  consists  of 
an  iron  cup  or  hemisphere,  with  suitable  openings  for  the  admission 
of  heat  from  below,  supported  by  another  iron  cup  attached  to  an  im- 
proved Bunsen  burner  and  rotating  on  it.  The  upper  hemisphere  is 
capable  of  being  swivelled  or  tilted  in  any  position  desired  to  facilitate 
the  flowing  of  the  solder  and  to  bring  all  parts  under  the  action  of  the 
blowpipe. 

The  cup  is  filled  with  pieces  of  broken  pumice  or  coils  of  asbestos 
rope,  upon  which  the  case  rests.  To  dry  out  an  invested  denture  it  is 
arranged  in  the  cup,  the  burner  lighted,  and  the  cover  placed  on  to 
retain  the  heat.  After  thoroughly  drying,  which  should  be  preliminary 
to  the  final  heating,  the  temperature  should  be  raised  by  increasing  the 
flow  of  gas  until  the  whole  piece  has  assumed  a  dull-red  appearance, 
when  the  top  cover  may  be  removed,  the  cup  tilted  to  a  convenient 
position,  the  blowpipe  brought  into  use,  and  the  soldering  finished. 
The  burner  underneath  should  remain  lighted  during  the  entire  opera- 
tion. The  position  or  angle  of  the  cup  may  be  changed  by  a  slight 
pressure  with  the  blowpipe  on  its  flanged  edge. 


Fig.  72. 


Fig.  73. 


Fig.  74. 


Suitable  solder  tweezers,  designed  respectively  for  placing  pieces  of 
solder  upon  parts  to  be  united  and  for  holding  gold  crowns  or  other 
small  articles  while  soldering,  are  important  accessories  of  the  soldering- 


WIRE  CLAMPS. 


57 


table.  Figs.  72-74  show  the  ordinary  forms  of  the  first,  and  Figs.  75- 
78  those  more  recently  designed  particularly  for  use  as  holders  in  the 
construction  of  metallic  caps  and  crowns. 


Fig.  75. 


Fig.  76. 


Fig.  77. 


Fig.  78. 


Round  point. 


Angular  point. 


Flat  point. 


Hawk  bill. 


Wire  clamps  are  indispensable  in  a  certain  class  of  soldering  opera- 
tions, and  a  small  collection  of  different  sizes  of  such  forms  as  are 
shown  in  Fig.  79,  made  of  No.  16  iron  wire,  should  always  be  kept  on 
hand  ready  for  use.  The  smaller  clamps  shown  in  the  illustration  are 
especially  useful  in  the  construction  of  lower  metallic  plates.  When  two 
thin  pieces  have  been  swaged  separately  v/ith  a  view  to  uniting  them  by 


58 


THE  MECHANICAL  LABORATORY. 


soldering,  there  is  always  danger  of  their  being  forced  apart  by  the  cal- 
cination of  the  borax  which  is  present  as  a  flux,  and  by  expansion  when 
the  heat  is  applied  :  it  is  necessary,  therefore,  to  hold  them  together 
temporarily  until  the  preliminary  or  partial  soldering  is  accomplished. 


In  soldering  a  chamber  cap  to  an  upper  plate  the  cap  is  almost  cer- 
tain to  change  its  relation  to  the  plate  during  the  soldering  unless  secured 
in  situ  by  a  stout  wire  clamp.  For  this  purpose  it  is  well  to  have  on 
hand  a  few  diiferent  sizes  of  the  larger  clamp  shown  in  Fig.  79. 


Fig.  80. 


Fig.  81. 


Fig.  82. 


Fig.  83. 


*i^*iLP- 


Dr.  George  W.  Mellott  has  devised  a  soldering  appliance  for 
use  in  crown-  and  bridge-work.  It  consists  of  a  support  made  of 
wound  asbestos  tape  surrounded  by  a  metal  band  (Fig.  <S0),  supplied 
with  loops  at  regular  distances  apart  for  the  reception  of  the  handle- 


SOLDERING   CLAMPS. 


59 


hooks  or  spring-clamps.  The  support  is  grooved,  so  that  the  heat  can 
pass  under  the  piece,  and  thus  heat  it  from  the  bottom  as  well  as  the 
top.  The  asbestos  support  is  about  4^  inches  in  diameter.  The  con- 
struction of  the  support,  which  is  reversible,  makes  it  a  perfect  cushion 
into  which  pins  can  be  readily  thrust  to  hold  small  articles  while  being 
soldered.  One  face  is  grooved  for  soldering ;  the  other  has  a  depression 
for  a  melting-cup  in  which  small  quantities  of  gold  scraps  may  be  fused. 
Adjustable  feet  permit  the  support  to  be  set  up  away  from  the  table 
when  desired.  Fig.  80  shows  the  support  with  clamps  and  ring-holding 
device  in  position  ;  Fig.  82,  the  grooved  face  with  the  removable  rim 
(also  of  asbestos)  for  confining  the  heat ;  and  Fig.  83,  the  reverse  face 
with  cup  and  ingot-mould  attached.  The  ingot-mould  has  three  matrices 
of  different  shapes  and  sizes.     Fig.  81  shows  the  handle  separately. 

Fig.  84. 


Fig.  85. 


Fig.  86. 


The  soldering  clamps,  for  holding  gold  collar  crowns  and  caps  while 
being  soldered,  have  loops  in  the  arms.  These  loops  facilitate  placing 
the  clamps  in,  and  removing  them  from  the  handle,  and  afford  a  ready 
means  of  rotating  or  changing  the  position  of  the  work  under  the  blow- 
pipe flame.  The  slight  pressure  required  to  hold  the  work  is  secured  by 
pushing  the  shanks  into  the  handle,  the  spear  of  which  may  then  be 
fixed  in  the  asbestos  support  or  any  other  suitable  support.  The  left 
hand  by  this  means  remains  free  to  manipulate  the  solder,  while  the  blow- 
pipe is  directed  by  the  right  hand  as  usual.     The  handle  will 


receive 


60 


THE  MECHANICAL  LABORATORY. 


either  clamp-shank.  The  three  forms,  with  the  spurred  handle,  are 
shown  in  Figs.  84-86.  After  removing  the  investing  materials  from 
around  the  soldered  dentures — which,  however,  should  never  be  done  if 
porcelain  teeth  are  present  until  the  case  has  been  allowed  to  cool  slowly 
and  perfectly — it  may  be  placed  in  a  pickling  solution  composed  of  sul- 
phuric acid  1  part,  water  4  parts,  for  the  purpose  of  dissolving  the  fused 
borax  and  the  oxide  of  copper  which  darkens  the  surface  of  gold  or  sil- 
ver into  which  it  usually  enters  as  an  alloy.  Dilute  sulphuric  acid  will 
dissolve  both  at  ordinary  temperatures,  but  its  action  may  be  greatly 
hastened  by  heating  it  to  212°  F.  This  may  be  done  in  a  copper  pick- 
ling-pan,  such  as  is  sold  at  the  dental  depots  for  the  purpose  (see  Figs. 
87,  88),  or  in  a  Wedgwood  evaporating  dish,  similar  to  those  used  by 

Fig.  87. 


chemists.  Sulphuric  acid  is  corrosive  and  destructive  to  the  clothing ; 
hence  ordinary  glass  vessels  are  not  safe  in  which  to  heat  the  solution, 
on  account  of  their  liability  to  fracture,  and  porcelain  ware  of  the  quality 


Fig. 


usually  made  for  domestic  use  will  not  retain  the  acid,  which  soon  dis- 
solves' the  glazing  from  the  surface,  after  which  it  is  liable  to  escape 
through  the  bottom  of  the  vessel. 

A  strong  solution  of  common  alum  may  be  used  instead  of  the  acid, 
but  it  requires  a  temperature  of  not  less  than  212°  F.  to  develop  its 
solvent  properties. 

When  the  same  pickling  solution  has  been  used  a  number  of  times  it 
becomes  quite  green  in  color  and  crystals  of  sulphate  of  copper  (CUSO4) 
form  around  the  edge  of  the  pan.  These  are  the  result  of  the  action  of 
the  acid  upon  the  oxide,  and  they  redissolve  when  the  solution  is  again 
heated.  The  sulphate  is  decomposed  by  electrolysis,  and  more  or  less 
metallic  copper  is  probably  always  deposited  upon  the  plate,  and  remains 
under  the  teeth  in  inaccessible  places  after  the  denture  is  finished ;  hence 
the  "coppery"  taste  sometimes  complained  of  in  newly-soldered  dentures 
when  first  inserted.  This  may  be  remedied  in  the  case  of  a  gold  denture 
by  immersion  in  a  weak  solution  of  nitric  acid  and  water ;  and  if  the 
denture  is  of  silver — which  metal  would  be  acted  upon  by  nitric  acid — 
boiling  in  a  strong  solution  of  alum  is  recommended. 


LATHES. 


61 


Lathes. — For  grinding  and  fitting  teeth  a  light,  easy-running  lathe, 
with  a  substantial  frame  of  iron  or  wood   2  feet   11  inches  high  to  the 


Fig.   89. 


centre  of  the  pulley-head,  which  will  permit  the  operator  to  sit  while  at 
work,  should  be  provided.  The  sit- 
ting position  saves  him  from  much 
of  the  fatigue  occasioned  by  con- 
tinuous work  of  this  kind,  while  it 
affords  the  steadiness  to  the  body 
and  hands  which  is  demanded  by 
the  delicate  and  precise  work  of 
fitting  teeth  to  gold  or  silver  plates 
and  to  each  other. 

The  centre  of  the  pulley-head 
should  be  not  less  than  6  inches 
from  the  top  of  the  lathe  table, 
which  should  be  formed  of  ash  or 
cherry  wood  26  inches  long  by  20 
inches  wide  and  If  inches  thick. 
The  frame  may  be  made  of  oak  or 
ash  wood  securely  fastened  together, 
or  a  lathe  table  similar  to  the  one 
shown  in  the  illustration  (Fig.  94) 
furnished  by  the  dental  depots  may 
be  employed.  The  latter,  when 
supplied  with  a  Lawrence  lathe- 
head  and  driving  wheel,  forms  an 
excellent  lathe. 

Many  of  the  lathes  now  offered 
for  sale  at  the  dental  depots  are  not 
entirely  satisfactory  either  for  fitting  teeth  or  polishing.     Their  driving 
wheels  are  either  too  heavy  or  too  light.     Valuable  improvements  have, 


62 


THE  MECHANICAL  LABORATORY. 


however,  been  made  recently.  Figs.  89,  90  illustrate  a  lathe  of  recent 
introduction  which  will  doubtless  answer  all  requirements  of  the  dental 
laboratory.     Fig.  91  shows  a  sectional  view  of  the  lathe-head  ;  Fig.  92 


Fig.  91. 


a  set  of  chucks  for  mounting  corundum  wheels  and  polishing  brushes, 
etc. ;  Fig.  93  a  reamer  for  fitting  wheels  having  wooden  centres  to  taper 
screw-chucks. 

A  lathe  intended  for  fitting  teeth  does  not  require  great  speed  or 
much  power.  A  good  lathe  may  be  made  by  obtaining  the  frame  and 
driving  wheel  of  one  of  the  inexpensive  form  of  amateur  turning  lathes 
now  in  the  market,  and  adjusting  a  Lawrence  head  to  it.     The  working 


parts  of  the  lathe  should  be  kept  clean,  well  oiled,  and  protected  as  far 
as  possible  from  abrading  powders  and  others  gritty  particles  with  which 
it  is  constantly  surrounded.  In  perhaps  the  majority  of  dental  labora- 
tories but  one  lathe  is  used  for  all  purposes  of  grinding  and  polishing.  It 
is  much  better,  however,  to  have  a  larger  and  stronger  lathe  for  polish- 
ing purposes  exclusively,  and,  as  greater  speed  is  required  for  this  pur- 
pose, it  should  be  about  3  feet  10  inches  in  height  to  the  centre  of  the 
pulley-head,  so  that  the  operator  may  stand  while  using  it :  the  form  of 


LATHES  INTENDED  FOB  FITTING   TEETH.  63 

lathe-head  shown  by  Fig.  95  will  answer  admirably.     The  fly  wheel 


( 


should  be  at  least  20  inches  in  diameter,  and  should  weigh  about  35 
pounds.     The  treadle  should  be  operated  by  a  lever  or  leg  motion,  and 


64 


THE  MECHANICAL  LABORATORY. 


not  by  what  is  known  as  the  heel-and-toe  treadle,  which  does  not  afford 
sufficient  speed  or  power.     The  lift  of  the  treadle  should  be  not  less 


than 


2|-  inches. 


One  of  the  most  valuable  applications  of  electricity  to  the  needs  of 
the  dentist  is  in  the  running  of  laboratory  lathes,  and  when  supplied 
with  the  110- volt  incandescent  current  such  an  apparatus  is  by  far  the 
most  convenient  and  effective  lathe  that  is  used  for  the  purpose  of  fitting 
teeth  or  polishing  dentures.  As  shown  by  Fig.  94  it  is  provided  with  a 
one-eighth  horse-power  motor  (C).     A  variable  resistance  (D)  is  inter- 

FiG.  95. 


posed  to  permit  the  lathe  to  be  run  at  different  speeds,  the  resistance 
being  operated  by  a  foot-pedal :  almost  any  desired  speed  can  be  had 
at  will  by  varying  the  pressure  on  the  pedal. 

The  polishing  lathe  should  be  provided  with  a  drawer  for  the  safe 
keeping  of  mandrels,  brush  wheels,  felt  and  cotton  wheels,  cones,  etc., 
together  with  the  abrading  and  polishing  powders  which  are  usually 
employed  in  the  final  finishing  of  the  different  kinds  of  laboratory  work. 
Corundum  wheels,  spatulas,  cements,  etc.,  used  in  fitting  and  attaching 
teeth  to  the  plate,  should  be  kept  in  a  drawer  attached  to  the  grinding 
and  fitting  lathe. 

The  corundum  wheels  so  extensively  used  in  the  dental  laboratory 
are  made  of  the  mineral  corundum  found  in  Ceylon  and  in  Pennsyl- 
vania, Georgia,  Massachusetts,  and  North  Carolina.  It  occurs  in  crystals 
of  the  form  of  double  six-sided  cones  of  various  sizes,  and  in  some  local- 
ities in  large  masses  without  crystalline  form.  Corundum  is  an  alumi- 
num oxide  having  the  formula  AljOg.  The  ruby  and  sapphire  are  trans- 
parent varieties  of  this  mineral,  their  color  being  due  to  the  presence  of 
a  small  amount  of  coloring  oxides.  Emery,  the  use  of  which  preceded 
corundum  as  an  abrasive  agent  in  the  dental  laboratory,  is  a  coarse 
variety  of  corundum.  Corundum  is,  with  the  single  exception  of  the 
diamond,  the  hardest  mineral  known.  It  is  prepared  by  pulverizing  the 
crystals  in  an  iron  mortar  by  successive  blows  of  a  heavy  steel  pestle. 


GRINDING  PORCELAIN  TEETH.  65 

The  three  grits  which  are  employed  in  making  wheels  for  dental  pur- 
poses are  obtained  by  passing  the  powdered  corundum  through  sieves  of 
different  degrees  of  fineness  ;  they  are  known  as  fine,  medium,  and 
coarse.  The  latter  will  cut  most  rapidly ;  the  finest  will  not  cut  so  fast, 
but  will  leave  a  much  finer  surface.  The  powdered  corundum  is  mixed 
with  finely-ground  gum  shellac  in  the  proportions  of  3  ounces  of  corun- 
dum to  1  of  shellac ;  this  is  carefully  heated  and  thoroughly  mixed  until 
it  becomes  of  a  doughy  consistence,  when  it  is  put  into  an  iron  mould 
made  in  two  parts,  previously  oiled.  This  mould  is  placed  in  a  small 
press  and  force  enough  applied  to  consolidate  and  distribute  the  mixture 
into  all  parts  of  the  mould.  Too  much  force  should  be  avoided,  as  it  is 
liable  to  drive  out  so  much  of  the  shellac  that  the  particles  of  corundum 
will  not  be  sufficiently  adherent — a  condition  which  will  greatly  lessen  the 
wearing  qualities  of  the  wheel.  After  the  wheel  has  been  removed  from 
the  mould,  which  is  done  by  tapping  the  latter  sharply  with  a  wooden 
mallet,  it  is  washed  in  alcohol  for  the  purpose  of  removing  the  shellac 
from  the  surface  and  leaving  the  wheel  in  a  sharp  or  gritty  condition. 

While  grinding  porcelain  teeth  the  corundum  wheel  must  be  kept 
constantly  wet  to  prevent  the  shellac  from  becoming  heated  by  friction 
— a  condition  which  instantly  impairs  its  cutting  properties.  Numerous 
appliances  have  been  devised  in  the  form  of  "  drip  cups  "  designed  to 
automatically  supply  sufficient  water  to  the  wheel  while  in  use  to  pre- 
vent heating ;  but  these  are  objectionable  in  more  than  one  respect,  and 
are  liable  to  obstruct  the  light  and  prevent  it  from  falling  directly  upon 
the  point  of  contact  of  the  tooth  with  the  wheel.  A  simple  dish,  oblong 
in  form,  with  the  dimensions  of  8  inches  in  length  by  5  inches  wide,  by 
2|  in  depth,  partially  filled  with  clean  water,  serves  as  a  good  hand-rest, 
while  a  piece  of  sponge  of  the  size  of  a  large  walnut,  which  the  operator 
will  soon  acquire  the  habit  of  holding  between  the  index  and  middle 
finger  of  the  right  hand  while  he  keeps  it  in  contact  with  the  corundum 
wheel,  is  an  excellent  means  of  conveying  water  to  the  wheel  and  pre- 
venting it  from  splashing  his  face  or  clothing. 

There  are  at  least  seven  sizes  of  corundum  wheels  made  for  dental- 
laboratory  purposes,  ranging  from  f  of  an  inch  in  diameter  to  2^  inches, 
but  the  author  has  found,  after  much  experience  in  fitting  carved  blocks, 
rubber  sections,  and  single  gum  teeth,  that  a  maximum  of  1  inch  in 
diameter  and  ^th.  of  an  inch  in  thickness  is  quite  large  enough  for  joint- 
ing purposes,  while  the  smaller  sizes,  which  are  indispensable,  are 
obtained  by  the  wearing  away  of  the  1-inch  wheels. 

In  finishing  dentures  the  first  step  is  the  proper  levelling  of  the  sur- 
face :  this  is  usually  done  in  metallic  cases  with  the  corundum  wheel, 
after  which  the  scratches  left  by  the  sharp  particles  of  corundum  should 
be  removed  by  a  keen-edged  vulcanite  scraper.  The  piece  is  then  ready 
for  the  "  Scotch  stone,"  a  soft  mottled  stone  much  used  by  silversmiths 
and  workers  in  the  precious  metals,  furnished  by  the  dental  supply- 
houses  in  pieces  of  6  inches  in  length  by  ^  inch  in  thickness.  This 
material  has  decided  abrasive  qualities,  and  is  used  chiefly  to  remove  the 
scratches  left  by  the  corundum  wheel  and  scraper :  it  produces  a  fine 
silk-like  surface  and  brings  the  case  to  the  point  Avhere  the  buff  wheels 
armed  with  the  coarser  powders,  such  as  pumice,  are  to  be  used  :  these 
produce  a  surface  which  may  be  highly  polished  by  the  brushes  which 


66 


THE  MECHANICAL  LABORATORY. 


should  follow  the  buff  wheels,  and  should  carry  the  finer  polishing 
powders  or  those  used  for  the  purpose  of  obtaining  high  lustre,  such  as 
calcined  buckhorn  when  the  case  is  of  gold  or  silver,  and  prepared  chalk 
when  it  is  of  vulcanite  or  celluloid. 

In  vulcanite  or  celluloid  work  the  corundum  wheel  need  not  be  used, 
the  scraper  being  sufficient  for  the  levelling  of  the  surface,  after  which 
the  finer  numbers  of  emery  paper,  Nos.  0  and  J,  are  employed,  until  all 
traces  of  the  scraper  are  removed,  when  it  is  ready  for  the  pumice  pow- 
der, which  is  generally  applied  with  a  small  stick  of  soft  wood,  such  as 
poplar  or  pine,  after  which  the  denture  is  ready  for  the  felt  or  other  kind 
of  bufp-wheel  and  fine  pumice. 

Buff-wheels  and  cones  are  made  of  felt,  cotton  duck,  leather,  soft 
wood,  cork,  disks  of  cloth  or  chamois  leather,  stitched  together,  etc. 
Felt  is  probably  the  best  of  the  various  materials  used  in  forming  buff- 
wheels  :  these  wheels  can  be  obtained  at  the  dental  depots  in  sizes 
ranging  from  1|^  to  2^  inches  in  diameter.  Buff-wheels  are  intended  to 
cut  and  not  to  polish.     They  are  usually  armed  with  pumice,  and  must 

be  kept  constantly  wet  while  in  use. 
The  best  size  of  buff-wheel  for  den- 
tal-laboratory use  is  If  inches  in 
diameter  by  |  of  an  inch  in  thickness. 
Smaller  sizes  are  obtained  by  the 
wearing  away  of  the  larger  wheels. 
They  are  easily  mounted  upon  the 
*^  screw-cone "  mandrel,  to  which  they  do  not  ordinarily  require  to  be 
cemented  or  shellacked.  An  ingenious  felt-wheel  chuck  has  been  sug- 
gested by  Dr.  F.  E.  Pomroy  :  it  is  provided  with  three  steel  pins  to  pre- 
vent the  wheel  from  revolving  on  the  screw  (Fig.  96). 


Fig.  96. 


Felt-wheel  chuck. 


Fig.  97. 


The  brush-wheel  is  employed  for  the  purpose  of  obtaining  a  still  finer 
surface  than  is  attainable  with  the  Scotch  stone  or  buff-wheel  and  for 
the  final  polishing.  There  is  quite  a  variety  of  forms  made  for  dental- 
laboratory  use,  beginning  with  the  wood-centre  brush-wheel  with  straight 
bristles  in  from  one  to  four  rows  (Fig.  97) ;  the  brush  wheel  with  con- 
verging bristles  (Fig.  98) ;  the  cup-shaped  wheel  with  from  one  to  four 
rows  of  bristles  (Fig.  99);  cup-shaped  bristles  with  long  wooden  shanks; 


FINISHING  POWDERS. 


67 


hub-shaped  with  straight  bristles  and  hub-shaped  with  converging  bris- 
tles, etc.  In  selecting  brushes  it  should  be  remembered  that  those  with 
coarse  bristles  are  to  be  employed  with  abrading  powders  of  the  class  to 
which  pumice  belongs,  while  those  with  soft  bristles  are  particularly- 


adapted  for  use  with  prepared  chalk,  rouge,  calcined  buckhorn,  etc.,  or 
wherever  a  high  lustre  is  to  be  attained.  Two  brushes  of  each  of  the 
Nos.  1,  2,  and  3,  one  coarse  and  the  other  soft,  with  three  rows  of  bristles, 
are  sufficient  for  finishing  entire  or  partial  dentures,  with  the  addition  of 


Fig.  99. 


1/ 


Cutting  powders 


Polishing  powders 


two  small  straight  brush-wheels  of  1 J  inches  in  diameter,  with  two  rows 
of  bristles,  for  finishing  places  in  the  denture  which  will  be  found  inac- 
cessible to  the  larger  wheels  and  for  polishing  crown-  and  bridge-work. 
Finishing  powders  are  divided  into  two  classes,  used  under  different 
conditions  and  serving  different  purposes.  The  following  partial  list 
gives  a  few  of  those  in  general  use  : 

f  Pumice, 

I  Emery, 

J  Corundum  flour, 

j  Arkansas  powder, 
Hindostan-stone  powder,   j 

[Tripoli,  J 

(  Calcined  buckhorn,  ] 

J  Rotten-stone,  !  used       comparatively 

j  Prepared  chalk,  j  dry. 

l^Eouge,  I 

Emery  with  oil  has  long  been  used  by  workers  in  the  precious  metals 
for  cutting  down  the  surface  of  gold  and  silver  preparatory  to  the  final 


^  used  with  a  lubricant. 


68  THE  MECHANICAL  LABORATORY. 

polishing,  but,  as  it  is  nearly  black  and  liable  to  discolor  the  joints  of 
the  teeth,  it  is  an  objectionable  mixture  to  employ  in  the  finishing  of 
artificial  dentures ;  hence  its  place  has  almost  entirely  been  taken  by 
pumice  powder,  with  Castile  soap  and  water  as  the  lubricant.  Emery  is 
perhaps  better  suited  for  finishing  continuous-gum  cases,  which,  having 
no  joints,  are  not  liable  to  the  same  danger  of  discoloration  as  are 
dentures  formed  of  single  gum  teeth ;  platinum,  of  which  the  plates  of 
this  kind  of  dentures  are  made,  resists  attrition  to  a  greater  extent  than 
does  gold  or  silver  :  it  therefore  requires  a  more  decidedly  abrasive  pow- 
der than  would  suffice  for  either  of  those  metals  to  produce  smoothness 
enough  for  the  final  polishing. 

Of  the  polishing  powders  properly  so  called,  calcined  buckhorn  has 
been  found  of  so  much  value  as  an  agent  in  the  production  of  high 
lustre  in  gold  and  silver  work,  that  it  has  almost  entirely  superseded  the 
use  of  the  burnisher.  It  is  applied  with  a  soft  bristle  brush-wheel, 
similar  to  Fig.  99,  revolving  at  the  highest  speed  attainable.  The  pow- 
der is  at  first  slightly  moistened  with  water,  but  as  the  lustre  appears  it 
is  taken  up  between  the  tips  of  the  fingers  and  dropped  in  a  perfectly 
dry  condition  upon  the  plate. 

Rotten-stone  is  also  an  excellent  polishing  powder,  but,  like  emery,  it 
is  liable  to  discolor  the  joints  and  to  find  its  way  behind  the  backings  in 
soldered  work,  and  effect  more  or  less  change  in  the  color  of  the  teeth. 
It  has  therefore  nearly  gone  out  of  use  as  a  polishing  material  in  the 
dental  laboratory. 

Prepared  chalk  is  as  effective  an  agent  in  polishing  vulcanite  and  cel- 
luloid work  as  buckhorn  is  with  the  precious  metals.  It  is  also  applied 
mixed  sparingly,  at  first,  with  water,  on  a  No.  3  soft  bristle  brush-wheel 
tmtil  a  high  polish  begins  to  appear,  when  it  is  dropped  in  a  quite  dry 
state  upon  the  plate  while  in  contact  with  the  rapidly  revolving  brush- 
wheel. 

There  is  always  some  danger  of  heating  vulcanite  plates  if  held  with 
force  against  a  rapidly  revolving  brush-wheel :  the  frequent  unaccount- 
able warping  of  vulcanite  dentures  may  possibly  be  due  to  this  cause ;, 
such  an  accident,  however,  need  not  occur  if  ordinary  care  is  observed 
in  allowing  merely  the  ends  of  the  bristles  to  come  lightly  in  contact 
with  the  plate. 

Rouge  is  a  valuable  polishing  powder  for  gold  and  silver,  and  is 
much  used  by  jewellers.  It  is  moistened  with  alcohol  and  applied  spar- 
ingly to  a  cotton  buif-wheel  running  at  high  speed.  Care  should  be 
taken  to  keep  it  from  the  joints  in  single-gum  teeth  dentures,  as  its 
removal  is  a  matter  of  some  difficulty.  Calcined  buckhorn  has  to  a 
considerable  extend  superseded  it  on  account  of  its  greater  cleanliness^ 

The  use  of  the  burnisher  as  a  means  of  obtaining  high  lustre  in 
metallic  dentures  has  been  almost  entirely  abandoned,  because  of  its 
tendency  to  spring  or  warp  metallic  objects  to  which  it  is  applied,  and 
of  the  fact  that  it  is  unnecessary. 

Adhesive  wax — or  rosin-and-wax  cement,  as  it  is  sometimes  called — 
which  is  used  for  the  purpose  of  uniting  parts  of  work  preparatory 
to  its  investment  for  soldering,  such,  for  instance,  as  a  clasp  to  a  plate 
when  it  is  necessary  to  maintain  the  precise  relation  of  one  to  the  other 
until  permanently  fixed  by  soldering,  and  for  temporarily  fastening  teeth 


FLUXED    WAX.  69 

to  plates  while  arranging  and  adjusting  them  to  the  mouth — is  an  indis- 
pensable adjunct  to  the  dentist's  work-bench  and  lathe.  Adhesive  wax 
is  usually  composed  of  rosin  3  ounces,  wax  1  ounce.  The  proportions 
vary  with  the  season,  the  quantity  of  wax  being  reduced  to  half  an  ounce 
for  use  in  hot  weather  or  when  the  "  cement "  is  found  to  be  too  plastic 
and  yielding  for  satisfactory  use.  Mastic  and  dammar  are  also  occasion- 
ally added  to  the  above  formula  for  the  purpose  of  stiffening  it.  To 
prepare  the  cement,  melt  the  rosin  and  wax  in  a  suitable  vessel,  and  stir 
until  the  two  are  thoroughly  mixed ;  test  pieces  should  be  drawn  out 
into  sticks  and  allowed  to  chill,  when,  if  found  to  be  but  slightly  brittle 
and  of  sufficient  toughness  to  hold  a  porcelain  tooth  or  clasp  in  their 
correct  relation  to  the  plate  while  being  removed  from  the  plaster  model, 
the  cement  may  be  poured  into  a  vessel  of  cold  water,  and  when  cool 
enough  to  handle,  but  still  somewhat  plastic,  it  is  to  be  worked  into 
sticks  of  about  the  size  of  an  ordinary  lead  pencil.  These  are  allowed 
to  become  quite  cold,  dusted  with  dry  plaster  to  prevent  them  from 
adhering,  and  laid  away  in  a  box  for  future  use. 

Rosin-and-wax  cement  is  greatly  improved  by  age ;  it  is  therefore  a 
good  plan  to  keep  on  hand  a  considerable  quantity  of  it.  Shellac  rolled 
into  rods  and  sealing-wax  are  often  of  value  when  used  to  reinforce  the 
adhesive  wax  when  temporarily  attaching  teeth  and  clasps  to  plates  pre- 
vious to  investing  for  soldering.  If  the  cement  shows  the  slightest  tend- 
ency to  yield,  a  small  quantity  of  shellac  or  sealing-wax  dropped  upon  it 
will  so  stiifen  it  that  the  denture  may  be  removed  from  the  model  with- 
out change  of  relation  between  the  plate  and  the  clasps  or  teeth. 

Fluxed  Wax. — This  preparation,  suggested  by  Dr.  Parr  for  attaching 
clamps  and  teeth  in  plate-  and  bridge-work,  is  put  up  in  boxes  and  is 
applied  with  a  hot  spatula.  It  is  said  to  set  quickly  and  to  hold  the 
teeth  and  clasps  firmly  for  trial  in  the  mouth  and  during  subsequent  sol- 
dering. The  "cement"  throughout  which  the  flux  is  distributed  is 
readily  burned  or  melted  out,  leaving  the  flux  (probably  finely-powdered 
glass  of  borax)  as  a  deposit  over  the  crevices  and  surfaces  to  be  joined, 
ready  to  perform  its  office  in  soldering.  Experts  in  crown-  and  bridge- 
work  seem  to  prefer  to  use  the  rosin-and-wax  cement  in  bulk,  from 
which  it  is  taken  up  and  applied  with  a  hot  spatula. 

Sticks  of  plain  wax  are  also  very  useful  in  "  waxing  up  "  vulcanite 
and  celluloid  cases :  these  may  be  made  of  the  waste  wax  which  is 
always  found  in  plentiful  quantity  about  the  office  and  laboratory. 

Sheet-wax  plays  an  important  part  in  the  preparation  of  artificial 
dentures  on  bases  of  fusible  alloys,  vulcanite,  and  celluloid,  and  for  addi- 
tions and  modifications  of  the  plaster  model  preparatory  to  moulding  for 
the  zinc  die.  The  ordinary  base-plate  supplied  by  the  dental  depots  is 
generally  too  thick  for  the  temporary  plate  of  either  of  the  cast  or  plastic 
bases.  It  may  be  safely  said  that  much  of  the  uncertainty  of  dental- 
laboratory  manipulations  with  these  materials  is  due  to  a  want  of  care 
in  the  preliminary  arrangement  of  the  wax.  For  some  unaccountable 
reason,  the  majority  of  mechanical  dentists  seem  to  think  it  necessary  to 
make  the  wax  plate  two  or  three  times  as  thick  as  the  denture  should  be 
when  finished,  and  after  the  vulcanizing  to  reduce  it  to  the  proper  thick- 
ness with  steel  burs  sold  for  the  purpose,  and  which,  on  account  of  the 
danger  when  they  are  used  of  cutting  through  the  plate,  should  have  no 


70 


THE  MECHANICAL  LABORATORY. 


Fig.  100. 


place  in  the  dental  laboratory.  The  preliminary  waxing  of  dentures  of 
this  class  should  be  done  with  such  care  and  precision  that  the  waxed 
piece  will  represent  not  only  the  exact  thickness  of  the  plate  when  fin- 
ished, but  all  the  irregularities  of  surface  which  are  found  on  the  plaster 
model.  The  rugse  and  other  prominences  of  the  mouth 
assist  in  enunciation  and  mastication,  and  should  be  rep- 
resented in  the  plate.  It  is  probable  that  when  so  ar- 
ranged artificial  dentures  feel  less  like  foreign  objects 
when  worn  in  the  mouth.  In  order  not  to  obliterate 
these  natural  irregularites  of  surface  the  waxing  should 
be  done  with  two  or  three  layers  of  wax,  not  much 
thicker  than  is  used  in  making  artificial  flowers,  laid  on 
separately  and  pressed  with  the  thumb,  after  being 
slightly  softened  in  the  flame  of  a  spirit  lamp  or  Bun- 
sen  burner,  until  in  complete  contact  with  the  palatal 
portion  of  the  model.  Any  desired  thickness  can  be 
obtained  by  additional  sheets  of  wax,  but  the  main 
point  to  be  gained  by  this  method  of  waxing  is  uni- 
formity of  thickness ;  and  if  the  waxing  is  artistically 
done,  little  or  no  scraping  or  finishing  will  be  needed 
after  vulcanizing  except  at  the  edges.  Indeed,  the  most 
skilful  workers  in  the  plastic  bases  have  demonstrated 
that  the  best  results  in  vulcanite  and  celluloid  work  is 
obtained  by  precision  in  waxing  and  the  use  of  tin  to 
prevent  contact  with  the  plaster  of  the  investment,  and 
to  afford  a  polished  surface  which  shall  need  but  little 
interference  by  the  scraper.  Sheet  wax  should  not  be 
over  the  ^^i\.  of  an  inch  in  thickness :  it  may  be  pre- 
pared by  dipping  a  square  piece  of  plate  glass  or  hard 

Fig.  101. 


wood  I  an  inch  thick,  previously  oiled,  into  melted  wax,  allowing  it  to 
cool  upon  the  slab,  and  repeating  the  dipping  until  the  desired  thickness 
is  attained,  after  which  it  is  stripped  oif,  trimmed  to  the  dimensions  of 
3  inches  square,  laid  in  a  box,  with  tissue-paper  between  the  sheets ;  and 
it  is  then  ready  for  use.     In  the  manipulation  of  wax  a  spatula  of  the 


BENCH  TOOLS,   ETC.  71 

size  and  form  shown  in  Fig.  100  is  indispensable,  as  is  also  a  lamp  or 
gas-burner  for  the  purpose  of  softening  the  wax  and  heating  the  spatula. 
Fig.  101  shows  a  small  Bunsen  burner  which  has  been  found  to  answer 
the  purpose  in  every  respect. 

Bench  Tools,  etc. — The  special  application  of  tools  will  be  found  in 
the  respective  chapters  devoted  to  the  particular  kinds  of  work  in  which 
each  is  used.  Our  remarks  here  will  therefore  be  confined  to  their 
selection,  care,  and  proper  use.  There  are  two  infallible  indications  of 
the  amount  of  training  and  skill  possessed  by  a  mechanical  dentist : 
(1)  The  condition  of  his  tools ;  (2)  the  state  of  the  model  after  he  has 
made  a  denture  upon  it.  Skilful  and  accurate  workmen  will  do  so  little 
damage  to  plaster  casts  while  constructing  plates  or  clasps  that  little  or 
no  evidence  of  their  having  been  used  will  be  apparent  after  the  work  is 
finished,  showing  that  the  tools  have  been  well  selected,  kept  in  good 
working  order,  and  correctly  applied. 

The  addition  of  all  the  instruments  and  appliances  used  in  crown- 
and  bridge-work  would  very  greatly  augment  the  list  of  laboratory 
tools,  but,  as  they  will  be  described  in  the  chapter  on  that  subject,  it  is 
thought  best  not  to  include  them  in  the  ordinary  equipment  of  the  dental 
laboratory,  which  should  consist  of — 

Plate  shears,  straight  and  curved. 

Pliers  (flat-nose),  in  at  least  three  sizes — one  pair  large  and  strong 
enough  to  be  used  in  drawing  wire. 

Pliers  (round-nose),  two  sizes. 

Pliers,  one  pair  with  one  beak  rounded  and  the  other  flat — very 
useful  in  fitting  clasps. 

Side-cutting  nippers  for  removing  that  portion  of  the  platinum  pins 
which  projects  beyond  the  backing. 

Punching  forceps,  for  punching  holes  in  gold  backing  for  the 
platinum  pins. 

Clasp-bending  forceps.  There  are  two  kinds  of  these  instruments 
made.     In  one  the  jaws  are  at  a  right  angle  with  its  long  axis,  as  shown 

Fig.  102. 


in  Fig.  102.  In  dental  catalogues  this  instrument  is  called  a  plate- 
bender,  although  it  is  probably  never  used  for  that  purpose,  but  when 
employed  to  give  a  concave  form  to  a  piece  of  clasp  gold,  so  that  it  may 
conform  to  the  convex  shape  of  a  molar  tooth,  it  will  be  found  to 
admirably  serve  the  purpose.  The  so-called  clasp-benders  of  the 
dental  depots  are  arranged    with  the  jaws  parallel  with  the  long  axis 


72  THE  MECHANICAL  LABORATORY. 

of  the  instrument,  shown  in  Fig.  103,  and  are  not  nearly  as  effective 
as  the  one  shown  in  Fig.  102. 

Fig.  103. 


Plate-nippers  are  employed  for  removing  redundant  portions  of  a 
plate,  which  they  do  more  rapidly  than  could  be  accomplished  with  files. 

Plate-burnishers,  straight  and  curved. 

Horn  mallet. 

Riveting  hammer. 

Draw-plate  for  reducing  the  size  of  wire. 

Screw-plate  and  taps,  useful  in  the  construction  of  regulating  fixtures. 

Plate-gauge,  standard  American. 

Solder  tweezers. 

Kingsley's  vulcanite  scrapers,  Nos.  1  and  2. 

Jeweller's  saw-frame  and  saws. 

Vulcanite  flasks  (see  chapter  on  Vulcanite  Work). 

Small  steel  cold  chisels  for  cutting  out  chamber. 

Small  hammer,  weighing  about  2  ounces,  for  use  with  cold  chisels. 

Round-edged  brass  chaser  for  use  in  forming  vacuum  chambers  and 
for  carrying  the  plate  into  deep  places. 

Hand  vice. 

A  small  variety  of  sizes  of  gravers,  chisel,  and  gouge  forms.  Those 
made  for  wood-engravers  are  well  tempered  and  answer  admirably  for 
dental  laboratory  uses.  The  graver  will  reach  places  during  the  finish- 
ing of  dentures  which  would  be  inaccessible  to  the  corundum  wheel. 
They  are  also  useful  in  correcting  slight  imperfections  in  zinc  dies. 

Files,  half  round,  5  or  6  inches  long,  moderately  fine  cut ;  round 
files,  small  variety,  ranging  from  6  to  12  inches  in  length,  coarse  and 
fine  ;  flat  files  with  safe  edge,  moderately  coarse  and  fine.  Files  should 
be  kept  in  a  suitable  rack,  and  not  in  a  drawer  with  pliers,  shears,  etc., 
as  contact  with  these  and  with  each  other  will  be  sure  to  damage  them. 

Triangular  steel  scraper  for  removing  file-marks  on  edges  of  plate 
and  backings. 

Gas-fitter's  pliers  for  occasional  use  in  tightening  the  bolts  of  vulcanite 
flasks  and  other  rough  work  which  would  damage  the  ordinary  bench 
pliers. 

Vulcanizer  (see  Vulcanite  Work). 

Vulcanite  files  (see  Vulcanite  Work). 

Brass  articulators  (see  chapter  on  Articulations). 

Chisels  for  trimming  around  the  teeth  in  vulcanite  work. 

Arkansas  stone  (to  be  used  with  oil),  6  inches  long  by  2  inches  wide. 

Small  anvil  set  in  lead. 

Scissors,  straight  and  curved,  for  cutting  patterns  for  plates,  etc. 

Several  points,  made  from  broken  excavators  or  worn-out  pluggers, 


BENCH  TOOLS,   ETC.  73 

used  for  marking  upon  gold  or  silver  plates,  picking  wax  or  cement  from 
invested  cases,  and  numerous  other  purposes. 

Blue  pencil  for  marking  plan  of  plate  and  clasps  upon  plaster 
models. 

The  use  of  bench  tools  should  be  strictly  confined  to  the  purpose  for 
which  they  were  designed.  They  should  be  carefully  kept  from  contact 
with  plaster  of  Paris,  the  fumes  of  acids,  and  particularly  from  chlorine 
as  evolved  from  nitro-hydrochloric  acid  in  the  quartation  process  of 
refining  gold,  which  readily  acts  upon  the  surface  of  steel  and  iron. 


CHAPTER    II. 

METALS  AND  ALLOYS  USED  IN   PROSTHETIC  DENTISTRY. 

By  Chaeles  J.  Essig,  M.  D.,  D.  D.  S. 


Metals  and  Alloys  used  in  Prosthetic  Dentistry. 

The  elements  known  at  present  number  sixty-seven,  divided  into  the 
metallic  and  non-metallic ;  of  the  former  there  are  fifty-twO;  as  folloAVS  : 

Names.  Symbols.  Atomic  weight. 

Aluminum Al 27.4 

Antimony Sb  (Stibium) 120. 

Arsenic As 75. 

Barium Ba 136.8 

Bismuth .    .  Bi 207. 

Cadmium Cd 111.8 

Csesium Cs 132.6 

Calcium Ca 40. 

Cerium Ce 140.4 

Chromium Cr 52. 

Cobalt      Co 58.& 

Copper Cu  (Cuprum) 63.2 

Davyum Da (?) 

Didymium D 145.4 

Erbium E 166. 

Gallium Ga 70. 

Glucinum Be  (Beryllium) 9. 

Gold Au  (Aurum) 196.2 

Indium In 113.4 

Iridium Ir 192.7 

Iron Fe  (Ferrum) 56. 

Lanthanum =    .  La 138.5 

Lead Pb  (Plumbum) 206.5 

Lithium Li 7. 

Magnesium Mg 24. 

Manganese      Mn 54. 

Mercury Hg  (Hydrargyrum) 199.7 

Molybdenum Mo      95.5 

Nickel Ni 58. 

Niobium Nb 94. 

Osmium Os 198.5 

Palladium Pd 105.7 

Platinum Pt 194.4 

Potassium K  (Kalium) 39. 

Ehodium Eh 104. 

Eubidium Eb 85.3 

Euthenium Eu 104.2 

Silver      Ag  (Argentum) 107.7 

Sodium Na  (Natrium) 23. 

Strontium •    .    .    .  Sr 87.4 

Tantalum Ta 182. 

Thallium Tl 203.7 

74 


PROPERTIES  OF  THE  METALS. 


75 


Terbium Ter 148.5 

Thorium Th • 233.4 

Tin ,  ■  .  Sn  (Stannum) 117.7 

Titanium Ti 49.8 

Tungsten W  (Wolframium) 183.6 


Uranium U 

Vanadium V 

Yttrium Y 

Zinc Zn 

Zirconium Zr 


239.8 
51.3 
89.8 
65. 
89.4 


Of  these,  only  fifteen  are  employed  in  their  metallic  condition  ;  they 


are — 


Antimony. 

Aluminum. 

Bismuth. 

Copper. 

Gold. 

Iridium. 

Iron. 

Lead. 


Magnesium. 

Mercury. 

Nickel. 

Platinum. 

Silver. 

Tin. 

Zinc. 


The  metallic  elements  are  divided  by  metallurgists  into  two  classes — 
the  noble  and  base  metals.  The  first  are  those  which  are  capable  of 
being  separated  from  combinations  with  oxygen  by  merely  heating  to 
redness ;  the  base  metals  are  those  whose  compounds  with  oxygen  are 
not  decomposable  by  heat  alone. 

The  noble  metals  are  ten  in  number,  as  follows : 


Mercury. 

Gold. 

Platinum. 

Palladium. 

Silver. 

Ruthenium 

Osmium. 

Rhodium. 
Iridium. 

Davyum. 

The  base  metals  are  further  subdivided  according  to  their  affinity  for 
oxygen  and  other  chemical  properties. 

Properties  of  the  Metals. — A  metal  may  be  defined  as  an  ele- 
mentary substance  usually  solid  at  ordinary  temperatures/  insoluble  in 
water,  fusible  by  heat,  and  possessing  a  peculiar  lustre,  commonly 
spoken  of  as  a  "metallic  lustre" — an  expression  sometimes  used  in 
describing  the  appearance  of  substances  which  present  a  similar  condi- 
tion of  surface.  To  these  qualities  must  be  added  those  of  conducting 
heat  and  electricity,  which  the  metals  possess  to  the  greatest  extent,  and 
their  power  of  replacing  hydrogen  in  chemical  reactions.  Another  cha- 
racteristic of  the  metals  is  their  basic  properties  when  united  with  oxygen. 

Arsenic  and  tellurium  are  by  some  chemists  regarded  as  intermediate 
links  between  the  metallic  and  non-metallic  bodies.  Watts'  Dictionary 
of  Chemistry  classes  tellurium  with  the  "  sulphur  family,"  in  consequence 
of  its  poor  conducting  qualities  and  the  acid  character  of  its  oxides. 
Bloxam  does  not  class  arsenic  with  the  metals,  and  states  that,  though 
"  some  authorities  class  it  as  such  on  account  of  its  metallic  lustre  and 
property  of  conducting  electricity,  yet  it  is  lacking  in  the  quality  of 


^  Mercury  is  an  exception,  being  fluid  at  the  ordinary  temperature. 
—  40°  F. 


It  freezes  at 


76  METALS  AND  ALLOYS. 

forming  a  base  with  oxygen,  a  property  common  to  all  true  metals,"  and 
expresses  the  belief  that  "  the  chemical  character  of  its  compounds  con- 
nect it  in  the  closest  manner  with  the  phosphorus  group. 

The  metals  are  all  quite  opaque,  with  the  single  exception  of  gold, 
which,  however,  is  only  transparent  in  leaves  of  a  highly  attenuated 
condition,  when  it  transmits  green  light.  It  is  believed  by  some  that 
the  absence  of  transparency  in  the  other  metals  may  only  depend  upon 
our  inability  to  obtain  them  in  a  sufficiently  attenuated  state. 

The  color  of  the  metals  ranges  from  the  pure  white  of  silver  to  the 
bluish  hue  of  lead.  Between  these  two  the  major  part  of  the  others  may 
be  found.  About  five  run  from  light  yellow  to  deep  red.  These  are- 
barium  and  strontium,  pale  yellow  ;  calcium,  somewhat  deeper  in  color ; 
gold,  when  pure,  of  a  rich  yellow ;  and  copper,  the  only  red  metal.  It 
was  at  one  time  supposed  that  the  mineral  titanium,  well  known  to 
dentists  as  a  dark-red  (copper-colored)  crystalline  substance,  used  in  a 
finely  divided  state  as  a  coloring  pigment  in  the  manufacture  of  porce- 
lain teeth,  was  a  metal.  Wohler  and  Deville,  however,  demonstrated 
that  the  red  mineral  is  an  oxide,  and  they  verified  their  statement  by 
producing  the  metal  itself,  which  is  of  a  steel-gray  color.  The  color  of 
the  metals  is  modified  by  alloying. 

Lustre. — This  characteristic  of  the  metals  is  probably  the  result  of 
perfect  opacity,  by  which  the  rays  of  light  are  reflected  from  the  sur- 
face. 

Odor  and  taste  are  possessed  by  a  few  of  the  metals.  The  greater 
number,  however,  are  destitute  of  these  qualities.  Iron,  copper,  and 
zinc,  when  heated,  evolve  peculiar  odors,  and  one  means  of  detection  of 
arsenic  is  the  odor  of  garlic  observed  when  that  metal  is  exposed  to  an 
elevated  temperature.  Odor  and  taste  may  depend  upon  voltaic  action. 
The  former  may  be  noticed  in  a  marked  degree  when  holding  in  the 
hand  a  mass  of  an  alloy  composed  of  gold,  platinum,  tin,  and  silver  pre- 
pared for  use  as  an  amalgam  alloy. 

Fusibility. — All  metals  admit  of  being  reduced  to  a  liquid  state  by 
the  application  of  heat,  but  the  temperatures  at  which  they  melt  diifer 
widely.  Thus,  mercury  retains  its  liquid  form  to  39°  F.  below  zero, 
and  is  always  fluid  at  ordinary  temperatures.  Potassium  and  sodium 
fuse  below  the  boiling-point  of  water ;  tin,  lead,  and  antimony,  below 
redness.  Gold,  silver,  and  copper  require  bright  redness.  Iron,  nickel, 
and  cobalt  fuse  at  white  heat,  while  platinum,  iridium,  rhodium,  titanium, 
etc.  become  fluid  only  when  exposed  to  a  powerful  voltaic  current  or 
the  flame  of  the  oxyhydrogen  blowpipe. 

Table  of  Fusing-points  of  the  Principal  Metals. 

Fahrenheit.  Centigrade, 

f  Mercury —39°  —39.44° 

Potassium      143.6  62. 

Sodium 203.8  95.6 

Tin 442.  227.8 

Bismuth 507.  264. 

Lead 619.  326. 

Arsenic  sublimes  without  fusion  at    356.  180. 

Zinc 773.  412. 

Antimony 842.  450. 

L  Cadmium 442.  227.8 


Fusible    below   red- 


SPECIFIC  HEAT. 


77 


Eed  heat : 


Highest  forge  heat : 


Agglomerate,  but  do 
not  melt  in  forge : 


Fusible  only  in  oxy- 
hydrogen  blow- 
pipe: 


Fahrenheit. 
(  Silver 1873. 

Copper 1996. 

Gold 2016. 

''  Cobalt,  rather  less  than  cast  iron. 

Iron  (cast) 2786. 

Iron  (pure) 2912. 

Manganese. 

Iron  (malleable). 

Nickel. 

Palladium. 

Molybdenum. 

Uranium. 
I  Tungsten. 
1^  Chromium. 

Titanium. 

Cerium. 

Osmium. 

Iridium. 

Ehodium. 

Platinum. 

Columbium. 

Tantalum. 


Centigrade. 
1023. 
1091. 
1102. 

1530. 
1600. 


Specific  Heat. — The  capacity  of  different  metals  for  absorbing  heat 
varies  with  each  metal.  This  is  demonstrated  by  the  amount  of  heat 
required  to  raise  equal  weight  of  different  metals  from  the  same  to  an- 
other given  temperature.  Thus,  if  we  express  by  1  the  quantity  of 
heat  necessary  to  raise  a  weight  of  water  from  0°  C.  to  1°  C,  that  which 
must  be  supplied  to  elevate  the  same  weight  of  the  following  metals  to 
that  temperature  would  be  as  follows : 


Mercury 0.03332 

Gold 0.03244 

Silver 0.0570 

Zinc 0.0955 

Cadmium 0.0567 

Copper 0.0952 

Tin 0.0562 

Platinum 0.0311 


Nickel 0.1086 

Cobalt 0.1070 

Iron 0.1123 

Lead 0.0314 

Palladium 0.0593 

Antimony 0.0508 

Bismuth, 0.0308 


If  we  should  take  equal  bulks  of  these  metals  and  expose  them  for 
the  same  length  of  time  to  exactly  the  same  heat,  and  then  place  them 
simultaneously  upon  an  arrangement  of  a  number  of  thin  sheets  of  wax 
separated  from  each  other  by  means  of  small  strips  of  wood  of  an  eighth 
of  an  inch  in  thickness,  it  would  be  found  that  the  number  of  sheets  of 
wax  perforated  will  vary  according  to  the  metal,  the  one  having  the 
highest  specific  heat  passing  through  the  greatest  number. 

Expansion  by  Heat. — Metals  expand  when  heated,  but  this  property 
is  not  uniform,  some  possessing  it  to  a  greater  or  less  extent  than  others. 
Within  certain  limits  of  temperature  this  takes  place  proportionately  to 
the  amount  of  heat  to  which  they  are  exposed.  Zinc  possesses  a  rather 
high  degree  of  expansibility,  and  is  consequently  useful  for  the  purpose 
of  making  dies  for  swaging  metal  plates  for  artificial  dentures.  By 
many  dentists  it  was  formerly  thought  that  a  metal  to  be  well  suited  for 
their  purpose  should  be  entirely  destitute  of  this  property,  so  that  after 
casting  the  die  should  not,  in  returning  to  its  former  condition  in  cool- 
ing, be  smaller  than  the  plaster  model,  the  object  per  se  being  to  have 
the  plate  fit  the  plaster  cast  perfectly  ;  whereas  the  real  purpose  should 


78 


METALS  AND  ALLOYS. 


be  to  make  the  plate  fit  the  mouth  closely,  the  plaster  model  being  only 
a  means  to  that  end.  Plaster  expands  in  setting.  From  the  impression 
to  the  model  two  expansions  are  gone  through  before  the  fac  simile  of 
the  mouth  in  plaster  is  obtained ;  hence  a  plate  made  to  fit  such  a  model 
perfectly  must  necessarily  be  somewhat  larger  than  the  mouth — a  con- 
dition unfavorable  to  atmospheric  adhesion.  On  the  other  hand,  a 
plate  made  to  fit  the  zinc  will  not  be  found  too  small  for  the  mouth,  but 
will,  provided  the  impression  is  a  good  one  and  represents  perfectly  the 
conformation  of  the  mouth,  afford  a  very  close-fitting  plate.  Even 
better  results  might  be  expected  where  the  plate  is  somewhat  smaller 
than  the  mouth,  because  such  a  condition  would,  in  entire  upper  den- 
tures, throw  an  undue  pressure  upon  the  alveolar  ridge,  while  that 
portion  of  the  plate  covering  the  palatine  arch  would  barely  be  in  con- 
tact with  the  tissues ;  the  pressure  along  the  ridge  would  quickly  pro- 
mote absorption  of  the  remains  of  the  alveoli,  and  a  uniform  adaptation 
of  the  plate  to  the  mouth  would  soon  follow.  On  the  contrary,  if  the 
plate  be  made  to  fit  the  plaster  cast,  and  is  a  trifle  larger  than  the  mouth, 
the  pressure  will  be  thrown  upon  the  palatine  arch  at  the  back  edge  of 
the  plate,  at  a  region  not  likely  to  change  by  absorption,  as  is  the  case 
with  the  alveolar  ridge,  and  hence  the  margin  of  the  plate  will  imbed 
itself  in  the  tissues  and  cause  much  discomfort  and  impair  the  usefulness 
of  the  denture. 

Much  time  and  thought  has  been  expended  in  the  effort  to  discover 
some  alloy  which,  in  connection  with  the  properties  of  hardness  and 
fusibility,  shall  possess  that  of  non-expansibility  when  heated.  Profes- 
sor Austen  published  a  table  of  the  more  fusible  alloys,  showing  the 
results  obtained  by  actual  experiments  with  reference  to  their  relative 
expansibility,  zinc  being  introduced  into  the  table  for  the  purpose  of 
comparison : 


1.  Zinc 

2.  Lead,  2  ;  tin,  1 

3.  Lead,  1  ;  tin,  2 . 

4.  Lead,  2 ;  tin,  3 ;  antimony,  1       

5.  Lead,  5 ;  tin,  6  ;  antimony,  1 

6.  Lead,  5 ;  tin,  6 ;  antimony,  1 ;  bismuth,  3 

7.  Lead,  1 ;  tin,  1  ;  bismuth,  1     .    .    •.    .    •   . 

8.  Lead,  5  ;  tin,  3  ;  bismuth,  8 

9.  Lead,  2 ;  tin,  1 ;  bismuth,  3 


Melting- 
point. 

Contracti- 
bility. 

Hardness. 

773"  F. 

.01366 

.018 

440 

.00633 

.050 

340 

.00500 

.040 

420 

.00433 

.026 

320 

.00566 

.035 

300 

.00266 

.030 

250 

.00066 

.042 

200 

.00200 

.045 

200 

.00133 

.048 

Brittle- 
ness. 


The  following  table  shows  the  relative  increase  in  length  of  a  bar  of 
the  metals  named  at  100°  Centigrade  whose  length  at  0°  C  is  1,000,000 : 


Platinum 1.00091085 

Palladium 1.00100000 

Antimony 1.00108300 

Wrought  iron 1.00124860 

Steel 1.00121286 

Gold 1.00149824 


Copper 1.00179673 

Silver 1.00200183 

Tin 1.00235840 

Lead 1.00285768 

Zinc 1.00297650 

Bismuth 1.00139200 


Power  of  Conducting  Heat — The  metals  are  the  best  conductors  of 
heat    among   the   solid   bodies.     The  quality  of  transmitting   heat   is 


POWER   OF  CONDUCTING  ELECTRICITY. 


79 


possessed  by  them  in  variable  degrees.  The  following  table  shows  the 
relative  approximate  ratio  of  conductivity  of  heat  of  each  of  the  metals 
commonly  used  in  the  mechanical  arts : 


For  heat. 

Silver 100. 

Copper   . 73.6 

Gold 53.2 

Tin 14.5 


For  heat. 


Iron  .  . 
Lead  •  • 
Platinum 
Bismuth 


11.9 

8.5 
8.4 
1.8 


Poivei^  of  Conducting  Electricity. — Metals  conduct  electricity  nearly 
in  the  ratio  of  their  capacity  of  transmitting  heat.  Among  the  results 
of  Matthiesen's  investigations  are  the  facts  that  debasing  a  metal  or 
alloying  it  greatly  diminishes  its  conducting  power,  that  elevation  of 
temperature  has  the  same  effect,  and  that  between  32°  and  212°  F.  (or 
0°  and  100°  C.)  great  diminution  takes  places — not  uniformly,  however, 
as  some  lose  it  more  in  proportion  than  others. 

The  relative  conducting  power  of  metals  may  be  observed  by  employ- 
ing equal  battery-power  upon  wires  of  the  same  diameter  of  different 
metals,  and  noting  the  length  of  the  portion  of  each  which  can  thus  be 
heated.  The  same  means  may  be  employed  to  indicate  the  quality  of 
electricity  or  the  capacity  of  the  battery  itself.  In  this  case  the  wire  is 
made  to  demonstrate  the  power  of  the  battery  by  the  length  of  wire 
which  the  battery  is  capable  of  rendering  incandescent. 

The  following  table  shows  the  relative  conductivity  of  some  of  the 
metals,  as  ascertained  by  Matthiesen  : 


For  electricity,  at  0°  C. 

Silver 100. 

Copper 99.95 

Gold 77.96 

Iron 16.81 


For  electricity,  at  0°  C. 

Tin 12.36 

Lead 8.32 

Platinum      18.80 

Bismuth 1.24 


Malleability,  Ductility,  and  Tenacity. — These  qualities  differ  widely 
in  the  metals.  The  term  malleability,  when  applied  to  such  a  metal  as 
gold,  signifies  that  by  hammering  or  rolling  its  surface  may  be  extended 
in  all  directions,  and  that  it  is  capable  of  being  thus  reduced  to  very 
thin  leaves  or  sheets  without  fracture  of  its  continuity  at  the  edges 
during  the  process  of  attenuation  ;  when  applied  to  other  metals  the  term 
should  be  understood  as  expressing  this  quality  relatively.  Gold  is  the 
most  malleable  of  the  metals,  and  is  capable  of  being  made  into  leaves 
^^  3  0  o\  0  0  ^^  ^^^  inch  in  thickness,  each  grain  of  which  will  cover  a  sur- 
face of  54  square  inches. 

In  the  following  list  the  metals  are  arranged  in  the  order  of  their 
malleability  : 


1.  Gold. 

2.  Silver. 

3.  Tin. 

4.  Copper. 

5.  Cadmium. 


6.  Platinum. 

7.  Lead. 

8.  Zinc. 

9.  Iron. 
10.  Nickel. 


11.  Palladium. 

12.  Potassium. 

13.  lodium. 

14.  Mercury  (frozen). 


Ductility  signifies  that  property  which  renders  a  metal  capable  of 
being  drawn  into  rods  or  wires,  usually  accomplished  by  passing  an 


80 


METALS  AND  ALLOYS. 


elongated  piece  of  metal  through  a  series  of  gradually  diminishing  holes 
in  a  steel  draw-plate ;  the  granular  particles  of  the  metal  are  thus 
extended  into  fibres.  One  grain  of  gold  has  been  drawn  into  a  wire 
550  feet  long.  To  accomplish  this  result  a  compound  wire  is  made,  of 
gold  covered  with  silver,  the  tenacity  of  the  latter  being  taken  advan- 
tage of  to  enable  the  gold  to  be  carried  through  the  successive  holes  of 
the  draw-plate  until  the  greatest  possible  attenuation  is  reached ;  after 
which  it  is  immersed  in  nitric  acid,  which  dissolves  the  silver,  leaving  a 
gold  wire  §  qVo"  ^^  ^^  hic^  in  diameter. 

In  the  following  table  the  metals  are  arranged  according  to  their 
ductility  : 


1. 

Gold. 

5.  Copper. 

9. 

Nickel. 

2. 

Silver. 

6.  Zinc. 

10. 

Palladium 

3. 

Platinum. 

7.  Tin. 

11. 

Cadmium. 

4. 

Iron. 

8.  Lead. 

Tenacity  is  the  power  possessed  by  metals  of  sustaining  weight  or  of 
resisting  rupture  when  a  bar  or  rod  is  exposed  to  tension.  As  the  fitness 
of  metals  for  certain  purposes  in  the  industrial  arts  depends  largely  upon 
this  property,  it  is  of  the  utmost  importance  to  know  the  relative  ten- 
acity not  only  of  the  different  metals,  but  of  different  alloys.  This  is 
usually  ascertained  by  preparing  wires  of  exactly  equal  diameters. 
These  are  suspended  by  one  end  from  a  fixed  bar,  and  to  the  other 
extremity  weights  are  gradually  and  carefully  added  until  the  wire 
breaks.  The  weight  which  causes  the  fracture  represents,  Avhen  com- 
pared with  other  wires  similarly  treated,  the  relative  tenacity  of  the 
metals.  Elevation  of  temperature  affects  the  tenacity  of  metals,  gene- 
rally diminishing  it.  On  the  other  hand,  malleability  and  ductility  are 
only  developed  in  some  of  the  metals  by  an  elevation  of  temperature. 
Thus,  it  was  found  that  zinc,  which  had  previously  been  of  no  use  in  an 
unalloyed  state,  was  rendered  perfectly  malleable  and  capable  of  being 
rolled  into  very  thin  sheets  merely  by  heating  to  between  248°  and 
302°  F.  (  =  120°  and  150°  C).  If  carried  much  beyond  this  point, 
however,  say  to  400°  F.  ( =  205°  C),  it  becomes  so  brittle  that  it  may 
be  reduced  to  powder  in  an  iron  mortar. 

Magnesium,  aluminum,  and  some  other  metals,  which  at  ordinary 
temperatures  are  nearly  destitute  of  ductility,  have  that  quality  greatly 
increased  by  heating,  and  are  then  readily  drawn  into  wire.  In  alloys 
these  qualities  are  diminished  by  heating. 

The  following  table  shows  the  order  of  relative  capacity  of  the  metals 
for  sustaining  weight : 


1.  Iron. 

4.  Silver. 

7.  Tin. 

2.  Copper. 

5.  Gold. 

8.  Lead 

3.  Platinum. 

6.  Zinc. 

It  must  not  be  assumed  that  the  three  qualities  of  malleability, 
ductility,  and  tenacity  are  possessed  to  an  equal  extent  by  each  metal. 
If,  however,  we  take  gold,  for  example,  the  most  perfectly  malleable  and 
ductile  of  the  metals,  we  shall  find  that  in  tenacity  it  ranks  considerably 


VOLATILITY.  81 

below  some  of  the  others,  and  the  greatest  care  is  necessary  in  dravv^ing 
a  piece  of  pure  gold  into  even  a  moderately  fine  wire,  and  beyond  a  cer- 
tain limit,  past  which  platinum  or  copper  may  be  carried  with  safety, 
gold  would  not  possess  sufficient  tenacity  to  overcome  the  resistance  to 
which  it  would  be  exposed  in  passing  through  the  smaller  holes  of  the 
draw-plate,  and  rupture  would  result. 

Iron,  on  the  other  hand,  which  exceeds  all  the  other  metals  in  ten- 
acity, is  in  malleability  inferior  to  gold,  silver,  copper,  platinum,  lead, 
zinc,  tin,  and  cadmium. 

Crystalline  metals,  such  as  bismuth,  antimony,  and  arsenic,  do  not 
possess  these  properties.  They  are  easily  broken  by  blows  of  a  hammer, 
and  the  two  latter  may  be  powdered  in  a  mortar. 

Crystallization. — Under  favorable  circumstances  probably  all  the 
metals  will  assume  a  crystalline  form.  Some  of  them,  as  gold,  silver, 
etc.,  are  found  native  as  cubes  or  octahedra  or  in  slight  modifications  of 
these  forms,  and  metals  in  a  crystalline  form  may  be  obtained  by  elec- 
trolysis. For  example,  silver  may  be  obtained  in  the  form  of  crystals 
nearly  pure  by  introducing  strips  of  copper  into  a  solution  of  argentic 
nitrate.  A  piece  of  zinc  introduced  into  a  solution  of  plumbic  nitrate 
will  precipitate  the  lead  in  the  form  of  feathery  crystals.  Gold  may  also 
be  deposited  in  this  form  from  solution  by  the  introduction  of  a  stick  of 
phosphorus.  Nearly  all  the  metals  yield  crystals  when  deposited  from 
their  solutions  by  electric  currents  of  feeble  intensity. 

Elasticity  and  sonorousness  may  be  conferred  upon  the  metals  by 
alloying.  Thus,  iron  does  not  possess  these  qualities  until  combined 
with  the  proper  proportions  of  carbon,  when  by  subsequent  tempering 
the  highest  degree  of  elasticity  is  developed,  and  pieces  of  steel  of  dif- 
ferent lengths,  as  arranged  in  the  dulcimer,  when  struck  with  a  small 
wooden  hammer  are  capable  of  giving  oif  the  most  musical  sounds. 
But  sonorousness  is  obtained  to  the  greatest  extent  in  alloys  of  copper 
and  tin  known  as  bell-metal.  A  very  great  amount  of  elasticity  is 
obtained  by  the  admixture  of  copper  and  zinc  in  the  form  of  brass,  from 
which  a  spiral  spring  may  be  made  superior  to  that  from  any  other  alloy, 
and  it  is  curious  to  observe  how  this  quality  may  be  developed  by  the 
admixture  of  two  metals  each  of  which,  examined  separately,  is  soft  and 
destitute  of  anything  like  springiness.  Thus,  gold  and  platinum,  both 
soft  metals,  when  combined  in  the  proportion  of  1  grain  of  the  latter 
to  1  dwt.  of  the  former  of  20-carat  fineness,  will  afford  a  decidedly 
elastic  alloy  suitable  for  clasps  for  artificial  dentures. 

An  elastic  alloy  may  be  formed  by  combining  platinum  with  a  small 
amount  of  iridium.  This  alloy  is  frequently  employed  in  the  construc- 
tion of  artificial  dentures. 

Volatility. — All  metals  are  probably  more  or  less  volatile,  although 
only  a  certain  number  admit  of  being  converted  with  any  degree  of 
facility  into  a  state  of  vapor,  even  at  the  highest  temperature.  Some  of 
the  conspicuously  volatile  metals  are  zinc,  cadmium,  mercury,  arsenic, 
tellurium,  potassium,  and  sodium,  while  a  few  others  have  the  property 
of  communicating  characteristic  colors  to  flame,  and  are  probably  volatile 
to  a  limited  extent. 

Metals  are  sometimes  characterized  as  "  fixed,"  as  gold,  copper,  nickel, 
etc.,  and   "  volatile "  (during  fusion),  as  cadmium,   zinc,  etc.     Arsenic 


82  METALS  AND  ALLOYS. 

may  unquestionably  be  regarded  as  belonging  to  the  latter  group,  passing 
as  it  does  without  fusion  from  the  solid  to  the  gaseous  state. 

Gold  has  been  known  to  volatilize  under  certain  conditions,  and  it  is 
doubtful  whether  it  is  at  all  volatile  by  itself ;  but  if  alloyed  with  copper 
it  has  been  shown  by  Napier  to  be  considerably  volatilized,  so  that  quan- 
tities amounting  to  4|  grains  could  be  collected  during  the  pouring  of 
30  pounds  weight  from  a  crucible.  According  to  Makins,  gold  has 
been  known  to  volatilize  when  mixed  with  silver  and  lead  and  the  metals 
cupelled  together,  he  having  collected  considerable  quantities  of  each 
metal  from  the  chimney  of  an  assay  furnace  after  only  a  few  weeks' 
use. 

Agents  which  may  Volatilize  a  Metal. — Concentration  of  solar  rays  in 
the  focus  of  a  lens ;  the  voltaic  current ;  the  oxyhydrogen  blowpipe 
flame.  The  three  have  been  employed  in  conjunction,  by  which  means 
magnesium  has  been  volatilized,  and  with  a  powerful  Bunsen  battery 
alone  carbon  has  been  reduced  by  volatilization  to  the  state  of  a  black 
powder. 

Alloys. 

Most  of  the  metals  are  capable  of  uniting  with  one  another,  forming 
a  class  of  compounds  termed  alloys,  in  which  may  be  observed  to  a 
greater  or  less  extent  the  properties  of  the  several  constituents  entering 
into  the  union. 

The  study  of  the  alloys  is  an  interesting  one,  as  they  are  not  only 
mixtures  of  the  metals  possessing  certain  distinct  qualities,  but  in  reality 
are  true  chemical  compounds.  In  the  appearance  which  often  accom- 
panies the  union  of  the  metals,  and  in  the  properties  of  the  resulting 
alloys,  we  may  frequently  observe  the  phenomena  which  characterize 
chemical  afinity,  such  as  heat  and  incandescence,  resulting  in  the  formation 
of  substances  having  a  definite  composition,  distinct  crystalline  form, 
and  properties  differing  from  those  of  their  constituents. 

Alloys  are  generally  harder  and  more  fusible  than  the  metals  of 
which  they  are  formed,  and,  as  many  metals  are  unfit  in  the  pure  state 
for  use  in  the  mechanic  arts,  owing  to  extreme  softness  or  high  fusing- 
point,  these  properties  are  modified  to  suit  various  requirements  by  the 
admixture  of  other  metals. 

Thus,  as  a  base  for  an  artificial  denture  pure  gold  would  be  too  soft 
to  withstand,  without  bending,  the  force  to  which  the  fixture  would  be 
exposed  during  mastication  ;  but  by  the  addition  of  sufficient  copper  and 
silver  to  reduce  the  gold  to  750  (18  carats)  the  necessary  rigidity  may  be 
obtained  without  materially  affecting  the  other  properties. 

Again,  it  is  often  desirable  to  unite  several  pieces  of  the  same  metal 
or  of  different  metals.  This  is  accomplished  by  means  of  a  class  of 
alloys  called  solders,  generally  formed  of  the  metal  upon  which  they  are 
to  be  employed,  with  the  addition  of  some  other  metal  which  will  con- 
siderably lower  the  fusing-point  without  affecting  the  color,  as  it  is 
desirable  that  the  place  of  union  should  not  be  noticeable.  For  example, 
a  solder  suitable  for  use  in  prosthetic  dentistry  should  fuse  at  a  much 
lower  temperature  than  the  plate  upon  which  it  is  to  be  used.  Its  color 
should  be  as  nearly  as  possible  the  same,  and,  what  is  even  more  import- 
ant, it  should  withstand  the  action  of  the  fluids  of  the  mouth  nearly  as 


ALLOYS.  83 

well.  These  properties  may  be  obtained  by  the  addition  of  small  quan- 
tities of  silver,  copper,  or  brass. 

The  value  of  many  of  the  metals  for  industrial  uses  is  very  greatly 
enhanced  by  alloying.  Thus,  copper,  which  is  unfit  for  casting  and  too 
tough  for  turning,  may  by  the  addition  of  zinc  be  rendered  not  only  harder 
and  more  elastic,  but  the  fusing-point  of  the  resulting  compound  will  be 
so  much  lower  than  that  of  the  copper  alone  as  to  render  the  casting  of 
it  a  matter  of  no  great  difficulty,  while  at  the  same  time  it  will  be  found 
susceptible  of  being  turned  in  the  lathe  with  facility. 

The  tendency  on  the  part  of  metals  to  unite  in  definite  proportions 
may  be  studied  in  connection  Avith  platinum,  iridium,  gold,  rhodium, 
ruthenium,  and  silver  when  fused  with  tin.  If  the  latter  metal  is  in 
excess  after  cooling,  a  metallic  ingot  is  obtained  resembling  closely  the 
tin  ;  but  by  the  action  of  strong  hydrochloric  acid  upon  this  the  excess 
of  tin  may  be  dissolved,  leaving  crystals  of  a  definite  alloy  of  the  tin 
and  the  noble  metal,  which  can  be  further  dissolved  by  the  same  acid, 
but  are  soluble  in  nitro-hydrochloric  acid  even  when  the  precious  metal 
contained,  whether  rhodium,  ruthenium,  or  iridium,  is  in  the  free  state 
absolutely  insoluble  by  that  agent. 

It  must  not,  however,  be  assumed  that  the  alloys  employed  in  the 
industrial  arts  are  the  result  of  definite  combination  dissolved  in  an 
excess  of  one  of  the  metals.  Many  combinations  are  capable  of  coexisting 
in  the  same  alloy.  This  may  be  demonstrated  in  an  alloy  of  tin,  lead,  and 
bismuth,  which  melts  below  the  boiling-point  of  water.  Heated  to  25°  C. 
and  then  permitted  to  cool,  it  will  be  observed,  by  the  assistance  of  the 
thermometer,  that  the  fall  of  temperature  is  twice  distinctly  arrested. 
The  cause  of  this  phenomenon  has  been  assumed  to  be  the  production  in 
the  compound  of  a  less  fusible  alloy,  which  in  solidifying  evolves  heat, 
and  thus  for  a  time  retards  the  gradual  cooling  of  the  mass.  It  may 
therefore  be  assumed  that  true  chemical  combinations  may  occur  between 
two  metals,  notwithstanding  the  fact  that  such  union  may  be  masked  by 
•excess  of  one  of  the  constituents. 

According  to  Matthiesen,  an  alloy  may  be,  first,  a  solidified  solution 
of  one  metal  in  another;  second,. a  chemical  combination;  third,  a  me- 
chanical mixture ;  or,  fourth,  a  solidified  solution  or  mechanical  mixture 
of  two  or  all  of  the  above.  In  simple  mechanical  mixtures  of  two  metals 
there  is  often  a  tendency  to  separate.  This  is  noticeable  in  some  alloys 
of  silver  and  copper  by  an  absence  of  perfect  homogeneity  in  the  ingot. 
Again,  some  of  the  metals  form  mixtures  so  decidedly  mechanical  that 
on  being  allowed  to  stand  after  fusing  they  will  separate,  the  one  possess- 
ing the  highest  specific  gravity  settling  to  the  bottom.  This  may  be 
observed  when  lead  and  zinc  are  mixed.  Matthiesen,  however,  found 
that  lead  retains  1.6  per  cent,  of  the  zinc,  while  the  zinc  retains  1.2  per 
cent,  of  the  lead. 

Density. — Theoretically,  it  might  be  supposed  that  the  density  of  an 
alloy  would  be  the  mean  of  its  constituents.  Such,  however,  is  not 
always  the  case,  as  the  resulting  number  is  sometimes  equal  to,  or  greater 
or  less  than,  the  theoretical  mean.  The  density  of  alloys  of  gold  and 
silver  is  less  than  the  mean  of  the  components,  in  consequence  of  expan- 
sion ;  while  brass  and  alloys  of  lead  and  antimony  vary  in  the  opposite 
xlirection  through  a  condensation  of  their  constituents.     But  in  the  for- 


84 


METALS  AND  ALLOYS. 


mation  of  some  alloys  there  is  no  alteration  of  volume,  and  the  density  of 
such  will  correspond  to  that  obtained  by  calculation  as  the  mean  of  their 
constituents : 


Alloys  having  a  greater  specific  gravity  than 
the  mean  of  their  components. 


Gold 

and  zinc. 

(( 

tin. 

(( 

bismuth. 

(I 

antimony. 

11 

cobalt. 

Silver 

zinc. 

lead, 
tin. 

It 

bismuth. 

Copper 

antimony, 
zinc. 

li 

tin. 

li 

palladium. 

ii 

bismuth. 

(I 

antimony. 

Lead 

bismuth, 
antimony. 

Platinum 

molybdenum 

Palladium 

bismuth. 

Alloys  having  a  tess  specific  gravity  than  the 
mean  of  their  components. 


Gold 

and  silver. 

(1 

"     iron. 

(f 

"     lead. 

11 

"     copper. 
■'     iridium. 

i( 

"     nickel. 

Silver 

Copper 

Iron 

"     copper. 
"     lead. 
"     bismuth. 

(1 
(I 

"     antimony. 
"     lead. 

Tin 

"     lead. 

a 

"     palladium 

li 

Nickel 

"     antimony. 
"     arsenic. 

Zinc 

"     antimony. 

Color  is  always  modified  by  alloying.  It  is  generally  such  as  might 
be  expected  to  result  from  the  mixture  of  the  metals  entering  into  the 
formation  of  the  alloy.  There  are  a  few  instances,  however,  where  it  is 
different.  Thus,  3  parts  of  silver  to  7  of  gold  yields  a  green  alloy,  and 
nickel  added  to  brass  produces  an  alloy  of  silvery  whiteness. 

Malleability,  Ductility,  and  Tenacity. — These  properties  are  generally 
much  changed  in  metals  by  alloying,  malleability  and  ductility  being 
diminished,  and  in  some  cases  entirely  destroyed,  even  in  the  combina- 
tion of  two  very  ductile  metals,  as  is  the  case  with  gold  containing  a 
small  quantity  of  lead,  ductility  being  completely  lost.  Again,  gold  and 
platinum,  two  exceedingly  ductile  metals,  are  rendered  much  harder  and 
somewhat  elastic  by  admixture. 

The  union  of  a  brittle  and  a  ductile  metal  yields  a  brittle  alloy. 
According  to  Mr.  Makins,  antimony,  a  metal  so  brittle  that  it  may  be 
broken  up  in  a  mortar,  when  added  to  gold  to  the  extent  of  ywo  P^^^ 
will  make  the  gold  quite  unworkable. 

Tenacity  is  generally  increased  by  alloying.  The  following  results 
were  obtained  by  Matthiesen  by  employing  wires  of  the  same  gauge 
and  noting  the  weights  which  caused  their  rupture  before  and  after 
alloying : 


Lbs. 

Copper,  unalloyed. 

25  to  30 ; 

alloyed  with  12  per  cent,  tin, 

80  to  90 

Tin, 

under    7 ; 

"         "             "              copper, 

7 

Lead, 

"        7; 

"      tin. 

7 

Gold, 

20  to  25 ; 

"         "      copper. 

70 

Silver           " 

45  to  50 ; 

"         "      platinum. 

75  to  80 

Platinum,    " 

45  to  50. 

Iron, 


80  to  90;         steel  (iron  alloyed  with  carbon),  above   200. 


Generally  speaking,  the  hardness  of  metals  is  increased  by  alloying^ 
them.     A  familiar  instance  is  standard  gold  or  silver.     Neither  of  these 


ALLOYS.  85 

when  unalloyed  is  sufficiently  hard  to  withstand  attrition  to  the  degree 
required  for  currency,  but  the  addition  of  one-tenth  of  its  weight  of 
copper  to  either  metal  increases  its  hardness  to  the  required  point. 
Ninety-four  parts  of  copper  with  6  parts  of  tin  form  an  alloy  so  brittle 
that  it  may  be  broken  with  a  hammer. 

Fusibility. — The  fusing-point  of  an  alloy  is  always  lower  than  the 
least  fusible  metal  entering  into  the  composition  of  the  alloy.  Thus,  an 
alloy  composed  of  5  parts  of  bismuth,  3  of  lead,  and  2  of  tin  melts  at 
91°  C,  less  than  the  boiling-point  of  water,  while  tin  alone  fuses  at 
227.8°  C.  and  lead  at  325°  C,  and  the  addition  of  a  small  amount  of 
cadmium  to  the  above  alloy  will  further  reduce  the  fusing-point  to  140° 
F.  or  60°  C  Lead  combined  with  a  small  portion  of  silver  is  more 
fusible  than  the  former  in  a  state  of  purity,  and  an  alloy  may  be  formed 
of  potassium  and  sodium  which  remains  fluid  at  ordinary  temperatures 
of  the  air. 

Decomposition. — When  the  alloy  contains  a  volatile  metal,  like  zinc 
or  mercury,  heat  decomposes  it ;  but  the  temperature  required  to  expel 
the  last  trace  of  the  volatile  metal  must  be  considerably  higher  than  that 
metal's  normal  temperature  of  ebullition.  If  the  alloy  is  composed  of  a 
noble  metal  and  zinc,  lead,  or  tin,  and  it  is  desired  to  free  it  from  the 
impurity,  this  may  be  accomplished  by  exposure  to  a  high  temperature 
and  the  addition,  while  the  metal  is  fluid,  of  some  substance  rich  in  oxy- 
gen, such  as  potassium  nitrate.  By  this  means  the  base  metal  is  con- 
verted into  an  oxide,  and  is  then  dissolved  and  held  in  solution  by  the 
borax  which  should  be  used  as  a  flux  in  the  crucible.  Metals  in  com- 
bination with  mercury  may  be  separated  by  the  application  of  heat,  the 
mercury  volatilizing  at  600°  F.  In  the  case  of  particles  of  amalgam, 
however,  the  temperature  to  which  the  pieces  are  exposed  should  be  at 
least  a  bright-red  heat. 

Infliienee  of  Constituent  Metals. — Mercury,  bismuth,  tin,  and  cad- 
mium give  fusibility  to  alloys  into  which  they  enter;  tin  also  gives 
hardness  and  tenacity ;  lead  and  iron  give  hardness  ;  arsenic  and  anti- 
mony render  alloys  brittle.  It  has  been  observed  that  phosphorus  and 
arsenic,  when  added  to  alloys  of  copper  and  tin,  have  the  power  of 
deoxidizing  or  eliminating  metallic  oxides,  which  are  invariably  present. 
The  well-known  phosphor-bronze  owes  its  closeness  of  grain  and  supe- 
rior tenacity  to  the  addition  of  phosphorus,  and  it  is  claimed  that  "  when 
arsenic  or  arsenical  compounds  are  made  to  unite,  under  suitable  condi- 
tions, with  alloys  of  copper  and  tin,  known  as  bronze  or  gun-metal,  it 
imparts  to  them  several  remarkable  and,  for  many  purposes  in  the  arts, 
desirable  properties — among  others  and  principal  of  which  are  homo- 
geneity, hardness,  elasticity,  and  a  peculiar  smoothness,  rendering  it  a 
valuable  anti-friction  metal  for  journal-bearings,  etc." 

The  arsenical  compounds  of  alloys  of  copper  and  tin  are  also  more 
fluid  when  molten  than  are  other  known  alloys  of  copper  and  tin — a 
property  which  renders  them  capable  of  filling  out  sharply  and  without 
flaws  the  most  intricate  moulds. 

Liquation. — The  constituents  of  an  alloy  heated  gradually  to  near  its 
point  of  fusion  frequently  unite  to  form  new  compounds,  and  if  the 
fluid  portion  is  poured  off,  there  remains  a  solid  alloy  less  fusible  than 
the  original.     Copper  is  separated  from  silver  by  this  process.     In  bars 


86  METALS  AND  ALLOYS. 

of  silver  alloyed  with  copper  a  curious  tendency  on  the  part  of  the  latter 
to  separate  and  aggregate  at  the  edges  as  the  fused  mass  assumes  the  solid 
form  has  been  observed.  Mr.  Makins  states  that,  as  a  result  of  careful 
examination  of  Mexican  dollars  and  crown-pieces,  he  found  the  vari- 
ation between  the  centre  and  edges  to  range  in  the  former  from  1  to  6, 
and  in  the  latter  from  1  to  4,  milligrammes.  He  gives  as  the 
average  of  a  number  of  experiments  on  twenty-four  crown-pieces  a 
mean  variation  of  2  milligrammes,  and  as  the  quality  in  which  the 
greatest  tendency  to  separate  is  shown  that  of  900  parts  of  silver  to 
100  of  copper. 

Temper. — Modified  conditions  of  hardness  and  elasticity  of  a  metal, 
it  has  been  shown,  may  be  obtained  by  mixture  with  other  metals  and 
by  sudden  variation  of  temperature,  as  in  the  case  of  the  alloy  of  94 
parts  of  copper  and  6  of  tin,  which  forms  a  bronze  so  brittle  that  it  may, 
when  heated  and  slowly  cooled,  be  pulverized  with  a  hammer ;  but  if, 
on  the  contrary,  it  is  cooled  rapidly  by  immersion  in  cold  water,  it 
becomes  malleable.  The  treatment  of  iron  mixed  with  carbon  (steel)  is 
just  the  opposite,  the  greatest  degree  of  hardness  being  attained  by 
suddenly  cooling  the  heated  mass. 

Preparation. — When  the  alloy  is  to  be  formed  of  a  noble  metal  and 
one  or  more  of  the  base  metals,  the  former  should  be  thoroughly  fused 
first ;  the  latter  is  then  added,  and  the  whole  covered  with  charcoal  to 
prevent  oxidation,  and  then  thoroughly  mixed  by  stirring  or  agitating. 

When  it  is  designed  to  lower  the  fusing-point  of  gold  or  silver  for 
use  as  solders  by  the  addition  of  brass,  etc.,  the  precious  metal  should 
first  be  thoroughly  fused  with  a  sufficient  quantity  of  borax ;  the  brass, 
in  the  convenient  form  of  wire,  should  then  be  quickly  thrust  into  the 
melted  gold  or  silver.  It  will  almost  instantly  mix  with  the  melted 
mass,  and  the  borax,  if  in  sufficient  quantity,  will  cover  the  liquid  alloy, 
and  thus  protect  it  from  oxidation  by  contact  with  the  atmosphere. 

The  action  of  acids  upon  alloys  is  generally  more  energetic  than  upon 
a  simple  metal,  but  it  varies  according  to  the  relative  amounts  of  their 
constituents.  Silver  alloyed  with  a  large  proportion  of  gold  is  protected 
from  the  action  of  nitric  acid.  Sometimes,  however,  the  reverse  of  this 
is  seen,  and  metals  which  are  totally  insoluble  in  certain  menstrua  are 
made  to  dissolve  in  them  by  the  addition  of  a  metal  on  which  they  have 
the  power  of  acting.  Thus,  platinum,  although  of  itself  insoluble  in 
nitric  acid,  may  be  dissolved  by  it  when  sufficiently  alloyed  with  silver. 

Alloys  consisting  of  two  metals,  one  readily  oxidizable,  the  other 
possessing  less  affinity  for  oxygen,  may  be  readily  decomposed  by  the 
combined  action  of  heat  and  air.  In  this  case  the  former  metal  will  be 
rapidly  converted  into  an  oxide,  excepting  perhaps  tlie  last  portions, 
which  may  in  some  degree  be  protected  from  further  action  by  the  oxide 
already  formed.  This  increased  affinity  for  oxygen  exhibited  by  alloys 
is  probably  an  electrical  phenomenon,  the  study  of  which  belongs  rather 
to  the  science  of  chemistry  than  to  metallurgy. 

The  composition  of  alloys  used  as  bases  for  artificial  dentures,  and 
those  employed  as  solders,  will  be  described  with  the  metals  forming 
their  bases. 

Solders  intended  for  use  in  dental  mechanism  should  possess  the 
quality  of  flowing  freely,  and  be  as  high  grade  as  the  attainment  of 


COMBINATIONS  OF  METALS,  87 

that  property  will  permit,  so  that  they  will  resist  the  action  of  the  fluids 
of  the  mouth.  They  should  also  approximate  as  nearly  as  possible  to 
the  color  of  the  plates  upon  which  they  are  used.  Gold  and  silver 
solders,  for  all  purposes  of  the  dental  laboratory,  should  be  in  the  form 
of  plate  of  about  No.  27  of  the  standard  gauge  in  thickness.  This  may 
be  conveniently  cut  into  portions  or  sizes  corresponding  to  the  extent  of 
the  parts  to  be  united.  Thus,  upon  each  pin  a  small  particle  of  solder 
should  be  placed,  just  large  enough  to  cover  it.  A  piece  of  the  same 
size  should  also  be  placed  near  the  top  of  each  joint  where  the  backings 
come  together,  while  a  larger  piece  should  be  placed  at  the  point  of 
union  between  backings  and  plate.  The  pieces  of  solder  are  made  to 
adhere  to  their  proper  positions  through  the  agency  of  the  borax,  which, 
as  described  in  the  preceding  chapter,  is  used  by  taking  a  lump,  rubbing 
it  on  a  piece  of  ground  glass  with  clean  water  to  a  creamy  consistence, 
and  then  applying  to  the  surface  by  means  of  a  camel's-hair  pencil. 

The  application  and  management  of  the  heat  in  operations  of  soldering 
are  matters  requiring  both  care  and  judgment.  The  temperature  should 
at  first  be  raised  very  gradually,  in  order  that  j)ieces  of  solder  may  not 
be  thrown  off  or  displaced  by  the  puffing  up  incident  to  the  calcination 
of  the  borax,  or,  in  the  case  of  an  artificial  denture,  that  the  porcelain 
teeth  may  not  be  fractured  by  a  too  sudden  elevation  of  temperature. 
Both  parts  to  be  united  should  be  equally  heated ;  therefore  the  heat 
should  be  so  applied  in  the  case  of  an  artificial  denture  as  to  raise  the  teeth 
and  plate  to  an  equal  temperature ;  otherwise,  should  the  plate  become 
sufficiently  hot  while  the  teeth  remain  comparatively  cool,  the  solder, 
when  the  flame  of  the  blowpipe  is  directed  upon  it,  will  flow  upon  and 
adhere  to  the  plate.  In  other  words,  it  will  manifest  a  preference  for  the 
hottest  portion.  The  failure  to  effect  an  equal  distribution  of  heat  pre- 
paratory to  soldering  is  often  the  cause  of  vexation  and  delay.  For 
example,  in  the  process  of  uniting  a  rim  to  a  plate  by  soldering,  the  rim, 
being  so  much  smaller  than  the  plate,  will  be  more  quickly  heated,  in 
which  event  the  solder  will  fuse  and  flow  upon  the  rim,  and  the  attempt 
to  unite  it  to  the  plate  will  not  be  successful.  But  to  avoid  such  a  result 
the  flame  of  the  blowpipe  should,  as  a  preliminary  step,  be  directed 
exclusively  upon  the  plate  until  it  has  been  heated  to  nearly  the  fusing- 
point  of  the  solder,  when  the  pointed  blue  flame  may  be  thrown  upon 
the  latter,  and  union  of  the  rim  and  plate  can  hardly  fail  to  take 
place. 

Combinations    of    Metals   -with   Non-metallic    Elements. 

The  metals  combine  with  non-metallic  elements  to  form  a  new  class 
of  bodies  wherein  none  of  the  characteristics  of  the  constituents  are 
discernible.  These  are  the  chlorides,  bromides,  iodides,  fluorides,  cyan- 
ides, oxides,  sulphides. 

Metals  also  form  definite  compounds  with  nitrogen,  phosphorus,  sili- 
con, boron,  and  carbon. 

Chlorides. — All  metals  combine  with  chlorine,  and  some  of  them  in 
different  proportions,  as  illustrated  by  the  stannous  and  stannic  chlorides, 
the  first  having  a  formula  of  SnClg,  while  the  composition  of  the  latter 
is  SnCl^.  The  capacity  of  the  metals  for  combination  with  chlorine  is  not 
uniform.  The  different  proportions  are  designated  by  the  following  terms : 


88  METALS  AND  ALLOYS. 

Monochlorides,  such  as  KCl. 
Dichlorides,  "       BaClg. 

Trichlorides,  "       AnCl,. 

Tetrachlorides,         "       SnCl^. 

The  chlorides  may  be  prepared  by  acting  upon  the  metals  with  nascent 
chlorine  developed  by  the  admixture  of  hydrochloric  and  nitric  acids  in 
the  proportions  of  2  volumes  of  hydrochloric  with  1  of  nitric  acid. 

The  rationale  of  the  action  of  chlorine  upon  metallic  oxides  is  that  it 
drives  out  the  oxygen  and  unites  with  the  respective  metals  to  form 
chlorides.  The  interchange  may  take  place  at  ordinary  temperature,  as 
in  the  case  of  silver  oxide,  but  in  others  an  elevation  of  temperature  is 
required. 

Many  metallic  chlorides  are  prepared  by  acting  upon  the  metals  with 
hydrochloric  acid.  Zinc,  cadmium,  iron,  nickel,  cobalt,  and  tin  dissolve 
readily  in  hydrochloric  acid,  with  liberation  of  hydrogen.  Sometimes  a 
chloride  is  obtained  by  substituting  one  metal  for  another.  In  this  way 
stannous  chloride  is  frequently  prepared  by  distilling  metallic  tin  with 
mercuric  chloride,  thus  : 

HgCl^  +  Sn  =  SnCl^  -\-  Hg. 

Chlorides  may  also  be  prepared  by  dissolving  a  metallic  oxide,  hydroxide, 
or  carbonate  in  hydrochloric  acid. 

Bromides. — Bromine  unites  directly  with  most  metals,  and  forms  com- 
pounds analogous  in  composition  and  general  properties  to  the  chlorides. 
Many  of  the  saline  springs  contain  native  bromides,  and  silver  bromide 
occurs  as  a  native  mineral.  The  affinity  of  bromine  for  the  metals  is 
inferior  to  that  of  chlorine,  and  the  latter,  with  the  aid  of  heat,  drives  out 
the  bromine  and  converts  the  substances  into  chlorides. 

Iodides  are  compounds  possessing  properties  analogous  to  those  of  the 
chlorides  and  bromides,  and  are  obtained  by  processes  similar  to  those 
which  yield  the  latter.  With  the  exception  of  those  of  gold,  silver,  plat- 
inum, and  palladium  they  are  not  decomposable  by  heat  alone. 

Fluorides  are  compounds  formed  by  heating  hydrofluoric  acid  with 
certain  metals  or  by  the  action  of  that  acid  on  metallic  oxides.  They 
may  also  be  formed  by  heating  electro-negative  metals,  such  as  antimony, 
with  fluoride  of  lead  or  fluoride  of  mercury.  The  fluorides  are  destitute 
of  metallic  lustre,  and  most  of  them  are  easily  fusible  and  bear  a  close 
resemblance  to  the  chlorides. 

MeialliG  oxides  may  be  variously  formed.  Some  metals  by  mere 
exposure  to  air  while  heated  lose  their  metallic  character,  and  by  com- 
bination with  oxygen  assume  a  totally  different  appearance.  There  are 
several  methods  of  forming  oxides  artificially,  and  some  oxides  are 
capable  of  being  converted  into  others  of  a  higher  degree.  Red  lead, 
for  instance,  is  thus  formed,  the  metal  being  just  heated  without  allow- 
ing it  to  fuse,  when  a  protoxide  of  a  yellow  color  is  formed ;  but  on 
further  exposure  to  a  temperature  of  315.5°  C,  with  free  access  of  air, 
additional  oxygen  is  taken  up  and  the  mass  assumes  a  brilliant  red 
color. 

Oxides  of  metals  are  also  formed  by  heating  a  nitrate  or  carbonate  to 
redness,  by  which  means  the  acid  will  be  evolved  while  the  oxide  re- 


COMBINATIONS  OF  METALS.  89 

mains.  Thus,  a  protoxide  of  lead  may  be  formed  by  heating  the  white 
carbonate  of  the  metal,  its  color  soon  changing  to  a  lemon-yellow  as  the 
acid  present  is  driven  off. 

Oxides  of  some  of  the  metals  are  formed  by  first  acting  upon  the 
metal  with  nitric  acid,  and  in  that  way  obtaining  a  nitrate,  which  is 
dried  and  heated  to  dispel  the  acid,  when  the  oxide  will  remain. 

If  we  deflagrate  some  of  the  metals  with  a  body  containing  a  large 
proportion  of  oxygen,  we  obtain  their  oxides.  Tin,  lead,  zinc,  etc.  are 
in  this  way  removed  from  alloys  in  which  they  enter  as  prominent  con- 
stituents. If  1  gramme  of  an  alloy  consisting  of  tin,  silver,  gold,  and 
platinum  be  placed  in  a  crucible  and  melted  with  borax,  and  then  crys- 
tals of  potassium  nitrate  added  to  the  fluid  mass,  the  tin  will  be  con- 
verted into  an  oxide  which  is  dissolved  and  held  by  the  borax  glass.  If 
this  part  of  the  process  be  thoroughly  performed,  the  remaining  button 
will  be  found  to  contain  only  the  noble  metals,  silver,  gold,  and  platinum, 
which  may  be  easily  separated  and  weighed,  thus  affording  a  very  simple 
method  of  quantitative  analysis  for  ascertaining  the  proportions  of 
amalgam  alloys. 

Metallic  oxides  in  the  form  of  hydrates  are  obtained  by  treating  an 
aqueous  solution  of  a  metallic  salt  with  an  alkali.  Thus,  the  hydrated 
sesquioxide  of  iron,  commonly  employed  as  an  antidote  in  arsenical 
poisoning,  is  produced  by  adding  ammonia  to  ferrous  sulphate.  Zinc 
sulphate  or  cupric  sulphate  by  the  addition  of  caustic  potassa  yields 
bulky  hydrated  oxides.  These  in  turn  may  be  converted  into  simple 
oxides  by  heat. 

Superficial  oxidation  may  occur  gradually  by  mere  exposure  to  air  at 
ordinary  temperatures,  and  the  action  will  be  accelerated  by  the  presence 
of  moisture.  It  frequently  occurs,  however,  that  metallic  objects  thus 
superficially  oxidized  are  so  protected  by  the  newly-formed  oxide  from 
further  access  of  air  that  oxidation  can  no  longer  go  on  ;  but  should  the 
rusted  or  tarnished  surfaces  of  an  iron  or  leaden  object  be  removed, 
oxidation  will  again  occur. 

Many  metallic  oxides  are  formed  during  fusion  of  the  metals.  Lead 
and  zinc  are  examples  of  this.  The  former  by  continued  exposure  to  a 
sufficient  degree  of  heat  may  be  entirely  changed  into  an  oxide,  and  the 
latter,  when  carried  to  a  temperature  much  above  its  fusing-point,  burns 
with  a  brilliant  light,  during  which  the  oxide  is  evolved  in  the  form  of 
Avhite  fumes,  the  incandescence  accompanying  the  combination  being  an 
evidence  of  the  intense  affinity  which  the  metal  at  an  elevated  tempera- 
ture has  for  oxygen.  The  familiar  experiment  of  converting  iron  into 
an  oxide  by  throwing  a  jet  of  oxygen  gas  upon  a  red-hot  bar  of  the 
metal  is  an  illustration  of  the  fact,  and  many  metallic  oxides  may  be 
formed  by  deflagrations. 

There  are,  however,  a  few  noble  metals  possessing  so  feeble  an  affinity 
for  oxygen  that  they  cannot  be  made  to  combine  directly  with  the  latter  : 
even  when  the  oxides  of  these  are  obtained  by  chemical  means,  the  metals 
separate  from  the  oxygen  upon  being  heated  to  redness.  Gold  and  plat- 
inum are  illustrations  of  this  class  of  metals.  The  latter,  which  is 
employed  as  a  base-plate  in  the  "  continuous-gum  process  "  and  for  pins 
in  artificial  teeth,  is  subjected  to  the  most  intense  furnace  heat  without 
the  slightest  oxidation  of  surface. 


90  METALS  AND  ALLOYS. 

Many  of  the  metallic  oxides  occur  in  nature,  a  number  of  the  metals 
being  reduced  from  natural  ones,  which  are  oxides  of  their  respective 
metals,  such  as  iron,  tin,  manganese,  chromium,  etc. 

Sulphides. — The  metals  unite  with  sulj)hur  and  form  a  class  of  com- 
pounds which,  in  a  chemical  and  economical  point  of  view,  are  almost 
as  important  as  the  oxides.  These  were  formerly  termed  sulphurets. 
Many  of  them  are  found  as  natural  ores,  and  are  generally  brittle  solids 
possessing  a  high  metallic  lustre,  the  latter  quality  being  so  marked  in 
some  that  they  have  been  mistaken  for  gold.  Sulphur  combines  with 
the  metals  in  varying  proportions,  and  it  may  be  observed  that  combina- 
tion takes  place  in  proportions  similar  to  the  oxides,  the  only  excej)tions 
to  this  analogy  being  the  alkalies  and  alkaline  earths,  these  being  but 
two  oxides  of  potassium,  sodium,  and  barium,  while  there  are  no  less 
than  five  sulphides  of  these  metals.  All  the  metallic  sulphides  are  solid 
at  ordinary  temperatures ;  most  of  them  fuse  at  red  heat,  and  some 
sublime  unchanged.  The  admission  of  air  to  the  heated  sulphides  is 
followed  by  their  decomposition  and  conversion  into  sulphates,  or,  if 
they  are  exposed  to  higher  and  continued  heat,  into  oxides.  The  sul- 
phates are  all  insoluble  in  water,  with  the  exception  of  those  of  iodine, 
potassium,  strontium,  barium,  and  calcium.  The  metallic  sulphides  may 
be  artificially  formed  by  the  following  processes  :  By  heating  the  metals 
or  their  oxides  with  sulphur,  and  from  the  sulphates  by  heating  them 
with  charcoal  or  in  a  current  of  hydrogen  through  their  solutions,  or  by 
adding  to  them  a  solution  of  an  alkaline  sulphide. 

Reduction  of  Metallic  Compounds, — The  term  "reduction,"  as 
used  in  metallurgy,  refers  to  the  different  methods  of  separating  a  metal 
from  its  natural  ores  or  from  combination  with  any  non-metallic  element. 
The  noble  metals,  for  example,  are  separated  from  oxygen  by  merely 
heating  to  600^  F.  (  —  315.5°  C).  Generally,  however,  the  joint  action 
of  heat  and  reagents  for  which  the  non-metallic  constituents  of  the 
compound  have  greater  affinity  are  required. 

The  recent  inventions  of  the  Messrs.  Cowles  of  Cleveland,  Ohio,  and 
of  Graetzel,  near  Bremen  in  Germany,  have  proved  to  be  most  important 
advances  in  metallurgy.  The  essential  feature  in  the  improvements  of 
these  gentlemen  is  the  application  of  the  intense  heat  of  a  current  of 
electricity  from  a  dynamo  machine  through  a  conductor  of  great  resist- 
ance in  the  presence  of  carbon.  Many  of  the  most  refractory  ores, 
which  have  hitherto  resisted  all  similar  attempts,  may  be  readily  decom- 
posed in  these  electrical  furnaces.  By  this  means  aluminum  is  now 
reduced  from  corundum. 

The  metallic  compounds,  whether  natural  or  artificial,  are  a  class  of 
bodies  formed  of  dissimilar  elements  held  together  by  the  force  of  chemi- 
cal affinity,  and  which  are  totally  unlike  either  of  their  constituents. 
This  affinity  varies  much  in  different  metals.  Gold,  for  instance,  pos- 
sesses very  feeble  affinities,  and  when  combined  with  chlorine  it  may  be 
partially  precipitated  by  mere  exposure  to  light  or  the  atmosphere.  The 
facility  with  which  it  often  passes  from  one  element  to  another  may  be 
observed  in  the  interesting  process  of  manufacturing  "  shredded  gold," 
in  which  an  acid  solution  of  the  trichloride  is  formed  and  slightly  heated 
in  a  glass  matrass ;  gum  arable  or  sugar  dissolved  in  water  is  then 
added,  when  beautiful  web-like  masses  of  pure  gold  are  seen  to  form  in 


COMBINATIONS   OF  METALS.  91 

the  liquid ;  but  unless  these  are  quickly  removed  by  means  of  a  glass 
spoon  or  dipper,  they  will  almost  instantly  dissolve,  and  the  gold  again 
unite  with  the  chlorine.  Lead,  tin,  zinc,  iron,  and  many  other  metals 
evince  stronger  affinities ;  hence  they  are  not  so  readily  reduced,  and 
require,  in  addition  to  heat,  the  presence  of  other  substances,  such  as 
coal,  coke,  charcoal,  etc.  In  other  words,  it  is  necessary  to  expose  them 
in  contact  with  some  reagent  between  which  and  the  non-metallic  con- 
stituents of  the  comjjound  superior  affinity  exists,  so  that  by  union  of 
these  the  metal  may  be  released.  A  familiar  instance  of  this  may  be 
found  in  the  case  of  lead  and  zinc  as  used  for  the  purpose  of  making 
dies  and  counter-dies  in  the  dental  laboratory.  When  these  metals  have 
been  overheated  or  subjected  to  frequent  or  long-continued  meltings, 
they  become  partially  oxidized  and  covered  with  an  earthy-looking  mass 
consisting  of  semi-oxidized  metal.  Further  exposure  to  heat  would  have 
the  effect  of  converting  this  into  an  oxide  of  a  higher  degree,  but  if  cov- 
ered with  finely-broken  charcoal  or  other  carbonaceous  substance,  such 
as  scraps  of  beeswax,  the  usual  expedient  of  the  mechanical  dentist,  the 
oxygen  will  be  extracted,  carbonic  acid  will  be  formed  and  evolved, 
while  the  metal  will  be  restored  to  a  free  state. 

Chlorides. — With  the  exception  of  the  chlorides  of  the  metals  of  the 
alkalies  and  earths  all  metallic  chlorides  are  decomposed  when  heated  in 
a  current  of  hydrogen,  hydrochloric  acid  and  the  pure  metal  being  the 
result.  The  chlorides  of  gold  and  platinum  are  decomposed  by  simple 
ignition. 

Argentic  chloride,  when  heated  on  charcoal  under  the  flame  of  the 
blowpipe,  yields  pure  silver  and  emits  an  odor  of  hydrochloric  acid. 
Placed  in  water  acidulated  with  sulphuric  or  hydrochloric  acid,  argentic 
chlorides  may  be  reduced  by  the  addition  of  pieces  of  some  easily  oxi- 
dized metal,  such  as  zinc  or  iron,  the  rationale  of  the  reaction  being  as 
follows :  The  zinc  displaces  the  hydrogen  of  the  H2SO4,  zinc  sulphate  is 
formed,  the  liberated  hydrogen  unites  with  the  chlorine  to  form  hydro- 
chloric acid,  and  pure  silver  remains. 

Sulphuric  acid  decomposes  the  chlorides  and  converts  them  into 
oxides,  the  oxygen  being  supjjlied  from  the  water  present.  Some  chlo- 
rides may  be  decomposed  by  heating  them  with  a  metal  which  has  more 
powerful  basic  properties.  Thus,  sodium  when  heated  with  aluminum 
or  magnesium  chloride  will  become  sodic  chloride,  with  liberation  of  the 
magnesium  or  aluminum.  Some  chlorides  are  reduced  by  heating  with 
a  mixture  of  sodic  carbonate  and  charcoal ;  other  carbonaceous  com- 
pounds, such  as  sodic  or  calcic  carbonate,  are  frequently  used. 

Sulphides. — Reduction  of  the  sulphides  of  the  noble  metals,  such  as 
gold,  silver,  mercury,  and  platinum,  is  completely  effected  by  heat  alone. 
The  oxygen  of  the  atmosphere  unites  with  the  sulphur,  which  is  evolved 
as  sulphurous  acid.  In  some  cases,  however,  a  portion  of  the  oxygen 
combines  with  the  metal,  and  an  oxide  instead  of  the  free  metal  is 
obtained.  The  application  of  heat  and  air  in  some  instances  converts 
the  sulphide  into  a  sulphate,  which  in  turn  may  be  decomposed  at  high 
temperatures  and  separated  into  sulphurous  acid  and  a  metallic  oxide. 
On  the  other  hand,  some  of  the  sulphides  may,  when  heated  with  access 
of  air,  be  converted  into  permanent  sulphates  capable  of  resisting  high 
degrees  of  heat. 


92  METALS  AND  ALLOYS. 

Metallic  iron,  hydrogen,  chlorine,  etc.  are  frequently  employed  as 
reducing  agents  to  combine  with  sulphur.  If  sulphides  of  lead  be 
heated  with  iron,  sulphides  of  iron  and  metallic  lead  result.  This 
method  is  frequently  practised  in  the  assay  of  galena,  clean  iron  nails 
being  heated  with  the  ore.  The  sulphides  of  antimony,  bismuth,  copper, 
tin,  and  silver  are  readily  reduced  by  passing  dry  hydrogen  over  them 
at  red  heat,  the  result  of  the  reaction  being  the  free  metal  and  sulphuret- 
ted hydrogen  and  sulphur.  Dry  chlorine  will  also  decompose  them,  and 
combine  with  both  the  metal  and  the  sulphur.  Nitro-hydrochloric  acid 
converts  the  sulphides  into  chlorides,  and  hydrochloric  acid  in  a  few 
instances  acts  similarly  :  its  hydrogen,  combining  with  the  sulphur,  is 
evolved  as  sulphuretted  hydrogen.  Strong  nitric  acid  also  decomposes 
them,  and  is  often  employed  in  analyses  of  ores.  The  sulphur  being 
thus  oxidized,  the  liberated  metal  combines  with  the  acid  to  form  a 
nitrate,  mercuric  sulphide  or  native  cinnabar  being  the  only  ore  which 
cannot  be  thus  reduced. 

Oxides. — The  reduction  of  lead,  zinc,  or  tin,  the  working  qualities  of 
which  have  been  impaired  by  frequent  meltings  with  exposure  to  air, 
may  be  effected  in  the  laboratory  by  placing  the  metal  to  be  treated 
either  in  a  large  clay  crucible  or  in  the  ordinary  iron  melting-pot  em- 
ployed by  dentists.  The  semi-oxidized  metal  is  then  covered  with 
powdered  charcoal,  when  the  reaction  described  above  takes  place,  and 
the  original  properties  of  the  metal  are  restored. 

There  are  some  oxides  to  which  the  foregoing  treatment  is  not  applic- 
able, but  these  may  be  reduced  by  passing  a  current  of  dry  hydrogen 
over  them  when  heated  to  redness.  Makins  gives  the  following  very 
clear  description  of  this  method  of  reducing  oxides  : 

"  A  large  two-necked  bottle  is  fitted  up  in  the  usual  way  for  the  evolu- 
tion of  hydrogen.  This  has  its  delivery-tube  passed  into  a  tube  filled 
with  fragments  of  calcic  chloride  for  the  purpose  of  absorbing  the  moist- 
ure which  may  be  carried  over  with  the  gas ;  to  the  other  end  of  this 
drying  tube  is  connected  the  tube  which  is  to  hold  the  metallic  oxide 
(generally  in  a  bulb  blown  upon  this).  The  gas-bottle  should  contain 
about  a  couple  of  quarts,  so  as  to  afford  a  steady  supply,  and  the  calcic- 
chloride  tube  should  be  long  and  well  filled.  In  operating,  after  the 
gas  has  completely  driven  out  the  air  in  the  apparatus  heat  is  applied 
to  the  bulb  containing  the  oxide,  and  its  reduction  will  be  brought 
about.  The  gas  must  be  kept  up  in  a  good  stream,  so  as  to  drive 
out  the  watery  vapor  formed  by  the  decomposition.  Here  the  hydro- 
gen takes  the  oxygen  of  the  oxide,  and  water  is  formed,  while  the  metal 
is  set  free." 

There  are  metals  whose  affinity  for  oxygen  is  so  strong  that  their 
union  with  that  element  cannot  be  broken  up  by  such  means  as  we  have 
described.  Deoxidation  of  these  metals  must  be  performed  through 
the  agency  of  some  other  metal  possessing  greater  affinity  for  oxygen. 
For  example,  if  oxides  of  iron  be  heated  with  potassium,  the  iron 
will  be  deoxidized,  Avhile  the  potassium  will  be  converted  into  potash 
(KP). 

Some  metallic  oxides  may  be  reduced  by  heating  with  sulphur,  part 
of  the  latter  abstracting  the  oxygen,  with  which  it  unites  to  form  sul- 
phurous acid.     A  portion  of    the   sulphur,   however,   unites  with   the 


GOLD.  93 

metal,  which  is  converted  into  a  sulphur  or  sulphate,  or  a  mixture  of 
both.  These  must  be  treated  according  to  the  directions  already  given 
for  the  reduction  of  metals  when  combined  with  sulphur. 

There  are  also  a  few  metallic  oxides  which  chlorine  gas  will  reduce. 
Thus,  platinum  is  liberated  from  combination  with  oxygen  when  exposed 
to  a  current  of  dry  chlorine. 

Probably  the  most  powerful  means  of  reducing  metals  from  com- 
bination with  non-metallic  elements  is  that  known  as  eleetrolysis.  It 
consists  in  exposing  a  solution  of  a  metallic  salt  to  the  decomposing 
influence  of  the  galvanic  current.  A  demonstration  of  this  force  may  be 
made  by  taking  a  solution  of  nitrate  of  lead  (plumbic  nitrate)  and 
immersing  in  it  a  piece  of  zinc.  The  latter  soon  becomes  covered  with 
needle-like  crystals  of  pure  lead ;  the  zinc  replaces  the  lead,  which  is  set 
free  and  deposited  at  the  point  of  galvanic  action.  Or  the  same  phe- 
nomenon may  be  witnessed  by  immersing  a  piece  of  clean  iron  in  a 
solution  of  copper  or  a  piece  of  copper  in  a  solution  of  salt  of  mercury, 
the  action  ceasing  when  all  the  metal  in  solution  is  reduced. 

Gold. 
Atomic  weight,  197.     Symbol,  Au  (Aurum). 

There  are  evidences  that  processes  of  alloying,  refining,  and  separating 
gold  were  practised  at  a  very  early  period  of  the  world's  history.  Ac- 
cording to  Pliny,  the  metallurgy  of  gold  was  known  in  his  day,  and  it 
was  employed  in  Rome  for  the  purpose  of  fixing  artificial  teeth  more 
three  hundred  years  before  the  Christian  era,  and  a  law  of  the  "  Twelve 
Tables  "  makes  exception  with  regard  to  such  gold,  permitting  it  to  be 
buried  with  the  dead.^ 

Occurrence,  Distribution,  and  Properties. — Gold  is  of  nearly 
universal  distribution,  and  is  found  in  nature  chiefly  in  the  metallic  state 
as  native  gold.  It  occasionally  occurs  in  combination  with  tellurium, 
lead,  and  silver,  forming  a  peculiar  group  of  minerals  confined  to  a  few 
localities  in  Europe  and  America,  these  being  the  only  certain  examples 
of  natural  combinations  of  the  metal.  The  most  important  minerals 
containing  gold  are  sylvanite  or  graphic  tellurium  (AgAu)Te2,  con- 
taining about  24  per  cent,  of  gold ;  calavesite,  AuTcg,  containing  about 
40  per  cent,  of  gold  ;  and  nagyagite,  or  foliate  tellurium,  the  compo- 
sition of  which  is  not  definitely  known.  It  contains  from  5  to  9  per 
cent,  of  gold.  The  metallic  sulphides,  such  as  galena  and  iron  py- 
rites, usually  contain  sensible  quantities  of  gold,  the  lead  ore  being 
almost  invariably  gold-bearing.  Native  arsenic  and  antimony  also  occa- 
sionally contain  gold,  and  a  native  gold  amalgam  has  been  found  in 
California. 

Gold  occurs  in  nature  very  nearly,  though  never  quite,  pure,  being 
generally  associated  with  silver.  Other  metals  are  occasionally  found 
combined  with  it,  but  in  very  small  quantities,  and  these  foreign  metals 
are  peculiar  to  localities.  California  gold,  in  addition  to  silver,  which  is 
always  present,  may  contain  iridium ;  Russian  gold  often  contains  plat- 
inum ;  and  specimens  of  the  native  metal  from  Brazil  are  frequently  found 
to  contain  palladium. 

1  Phillips'  Metallurgy. 


94 


METALS  AND  ALLOYS. 


Analyses  of  Native  Gold  from  Various  Localities. 

Gold.  Silver.      Iron. 
United  .States : 

California 90.12  9.01         6.15 

Europe : 

Vigra  and  Clogan 90.16  9.26      trace. 

Wicklow  (river) 92.32  6.17         0.78 

Transylvania 60.49  38.74       .    .    . 

Asia,  Russian  Empire: 

BeresofF 91.81  8.03       trace. 

Ekaterinburg 98.96  0.16  0.5 

Africa : 

Ashantee 90.05  9.94 

South  America  • 

Brazil 94.0  5.85 

Central  America 88.5  11.96 

Titiribi 76.41  23.12        .    .    . 

Cariboo 84.25  14.90        .    .    . 

Australia : 

South  Australia 87.78  6.07        6.15 

Ballarat 99.25  0.65 


Copper. 


trace. 


0.77 

.09 
0.35 


0.87 
.03 


Pure  gold  is  about  nineteen  and  a  half  times  as  heavy  as  water,  being, 
with  one  exception  (platinum),  the  heaviest  substance  in  nature.  It  is 
of  a  rich  yellow  color,  and  is  nearly  as  soft  as  lead.  These  properties 
are  all  sensibly  modified  by  admixture  of  other  metals.  The  tint  is 
lowered  by  small  quantities  of  silver,  and  heightened  by  copper.  Owing 
to  its  exceeding  softness,  gold  is  commonly  used  alloyed,  in  order  to 
render  it  capable  of  resisting  the  attrition  to  which  coins  and  articles  of 
jewelry  are  exposed.  It  is  the  most  malleable  of  all  the  metals.  One 
grain  may  be  beaten  into  leaves  which  would  cover  a  surface  of  56  square 

of  an  inch  thick. 


inches  and  only  300000 

Very  thin  gold-leaf  appears  yellow  by  reflected  and  green  by  trans- 
mitted light.  Highly  attenuated  films  of  gold,  when  heated,  transmit 
rays  of  light  of  a  ruby-red  color.  Gold  is  exceedingly  ductile,  but  does 
not  possess  a  very  considerable  degree  of  tenacity.  A  grain  of  gold, 
however,  if  covered  by  a  more  tenacious  metal,  such  as  silver,  may  be 
drawn  into  a  wire  five  hundred  feet  in  length.  It  also  possesses  the 
remarkable  property  of  welding  cold,  and  the  metal  in  the  state  in  which 
it  is  obtained  by  precipitation  by  oxalic  acid  may  be  formed  into  disks  by 
compression  between  dies. 

The  specific  gravity  of  gold  varies  according  to  condition.  In  the 
finely-divided  state  in  which  it  is  obtained  by  precipitation  by  oxalic  acid 
it  is  19.36.  The  specific  gravity  of  cast  gold  is  somewhat  less,  but  when 
compressed  between  dies  or  by  the  rolling-mill  it  may  be  raised  from 
19.37  to  19.41.  Annealing,  however,  will  restore  its  previous  density 
to  nearly  that  of  the  cast  metal.  The  atomic  weight  of  gold  is  197,  and 
its  fusing-point  is  1102°  C.  The  electric  conductivity  of  gold  is  given 
by  Matthiesen  as  73.96  at  15.1°  C,  pure  silver  being  100.  The  con- 
ducting power,  however,  depends  much  upon  the  degree  of  purity,  as  the 
smallest  addition  of  another  metal  will  very  considerably  lower  its  con- 
ductivity. 

The  conductivity  of  gold  for  heat  is  stated  as  53.2,  as  compared  with 
pure  silver,  100.     Its  specific  heat  is  0.0324. 

Volatility. — The  absence  of  uniformity  in  results  of  experiments  with 


GOLD.  95 

regard  to  this  property  given  by  different  investigators  would  seem  to 
leave  the  matter  still  in  doubt.  It  is  quite  probable  that  when  a  small 
portion  of  gold  is  mixed  with  a  large  quantity  of  zinc  and  heated  in  the 
air,  the  whole  of  the  gold  will  be  dissipated  with  the  fumes  of  oxide  of 
zinc.  Mr.  Makins  has  demonstrated  that  gold,  silver,  and  lead  when 
cupelled  together  volatilize.  Gold  may  also  be  volatilized  when  in  the 
form  of  leaf  or  highly -attenuated  wire  by  passing  a  powerful  charge  of 
electricity  through  it. 

Forms  of  Native  Gold. — The  native  metal  is  sometimes  found  in 
the  form  of  cubic  crystals,  in  octahedra,  and  in  irregular  and  more  com- 
plex shapes  called  nuggets  and  dust.  Crystals  of  gold  may  also  be 
obtained  artificially  from  an  amalgam  of  gold  1  part,  mercury  20  parts. 
The  mixture  is  maintained  at  a  temperature  of  80°  C.  for  eight  days. 
The  mercury  is  then  removed  by  strong  nitric  acid,  leaving  crystals  of 
gold,  which  require  to  be  heated  to  redness  to  develop  brilliancy  of 
surface. 

Gold  is  found  in  quartz  veins  or  reefs  traversing  slaty  or  crystalline 
rocks,  alone  or  associated  with  iron,  copper,  magnetic  and  arsenical  pyrites, 
galena,  specular  iron  ore,  and  silver  ores,  and  more  rarely  with  sulphide 
of  molybdenum,  tungstate  of  calcium,  bismuth,  and  tellurium  minerals. 
It  is  also  found  among  the  detritus  of  disintegrated  rock^,  associated  with 
the  metals  of  the  platinum  group.  In  the  superficial  alluvial  or  "placer" 
deposits  it  has  been  remarked  that  the  minerals  with  which  it  is  found 
intermixed  are  of  great  density  and  hardness,  and  are  the  most  durable 
constituents  of  disintegrated  rock. 

The  yield  of  gold  in  easily-worked  alluvial  deposits  is  often  exceed- 
ingly small.  It  is  stated  that  in  the  Siberian  gold-washings  the  propor- 
tion of  gold  ranges  from  12  grains  to  1  pennyweight  to  the  ton  of  sand, 
while  in  the  lodes  which  require  more  labor  to  work  the  proportion  is 
but  8  pennyweights  per  ton,  and  in  the  "  placer  "  washings  of  California 
it  is  but  12  grains  to  the  ton  of  gravel.  In  Australia  the  alluvial  wash- 
ings of  Victoria  yielded  25  grains  to  the  ton.  Vein-mining,  being  more 
difficult  and  costly,  necessitates  a  larger  yield  of  the  precious  metal,  and 
5  pennyweights,  or  about  five  dollars'  worth  of  the  gold,  is  in  most  gold- 
bearing  localities  regarded  as  a  paying  quantity. 

The  method  of  obtaining  gold  from  alluvial  deposits  is  exceedingly 
simple,  and  consists  in  washing  away  the  lighter  portions,  leaving  the 
heavy  metallic  particles.  In  the  early  days  of  gold-mining  in  California 
this  was  accomplished  by  means  of  a  pan  of  sheet  iron,  13  or  14  inches 
in  diameter,  held  in  the  hand  and  its  contents  exposed  to  a  stream  of 
w^ater ;  and  on  the  large  scale  consists  of  washing  the  alluvial  deposits 
into  sluices  or  troughs  by  means  of  continuous  streams  of  water,  mercury 
or  amalgamated  copper  plates  being  sometimes  employed  to  collect  the 
finer  particles  of  gold. 

In  vein-mining  the  separation  of  the  gold  from  the  rock  with  which 
it  is  mechanically  mixed  consists  in  reducing  the  latter  to  a  fine  powder 
in  grinding-  or  stamping-mills,  and  the  gold  is  recovered  by  amalgama- 
tion or  by  washing  the  pulverulent  mass  through  troughs  lined  with  coarse 
woollen  cloths,  by  which  means  the  lighter  deposits  are  carried  away 
with  the  current,  while  the  heavier  metallic  particles  become  entangled 

'  In  the  form  of  small  lumps  called  "dust." 


96  METALS  AND  ALLOYS. 

in  the  fibres  of  the  blanket,  until  the  surface  of  the  latter  is  completely 
covered,  when  it  is  removed  and  its  contents  are  washed  off  in  a  suitable 
vessel  and  reserved  for  amalgamation. 

In  the  treatment  of  gold  by  amalgamation  the  process  is  frequently 
retarded  by  a  difficulty  known  as  the  "  sickening  "  or  "  flouring  "  of  the 
mercury.  The  latter,  losing  its  bright  metallic  surface,  is  no  longer 
capable  of  coalescing  with  other  metals.  The  discovery  was  made  by 
Wurtz  in  1864  that  by  the  addition  of  a  small  quantity  of  sodium  to  the 
mercury  the  operation  is  greatly  facilitated,  the  addition  of  the  sodium 
preventing  both  the  conditions  above  referred  to,  which  are  produced  by 
certain  associated  minerals.  Some  metallurgists  recommend  the  addition 
of  20  per  cent,  of  zinc  and  10  per  cent,  of  tin.  It  has  been  estimated 
that  mercury  will  dissolve  from  0.05  to  0.08  per  cent,  of  native  gold  of 
standard  650  to  850  without  loss  of  fluidity.  The  solubility  of  the  gold 
increases  with  its  fineness.  When  the  point  of  saturation  has  been 
reached  lumps  of  the  solid  amalgam  are  introduced  into  an  iron  vessel 
lined  with  a  mixture  of  fire-clay  and  wood-ashes,  and  provided  with  an 
iron  tube  by  which  the  fumes  of  mercury  are  passed  through  water  and 
condensed,  the  distillation  being  effected  at  a  temperature  below  redness. 
The  gold  left  in  the  retort  is  then  melted  in  a  suitable  crucible. 

Gold  is  sometimes  reduced  from  the  mineral  by  exposing  the  ore, 
which  has  been  previously  roasted,  to  a  current  of  chlorine  gas.  By  this 
means  the  gold  is  converted  into  a  soluble  chloride,  which  is  removed 
by  washing  with  water.  The  precious  metal  is  then  recovered  in  the 
metallic  form  by  precipitation  with  ferrous  sulphate.  This  process  is, 
when  carefully  performed,  a  very  accurate  one,  and  yields  97  per  cent, 
of  the  gold  present  in  tlie  ore. 

Refining  Gold. — Methods  of  refining  gold  were  known  and  practised 
in  very  ancient  times,  and  many  of  them,  though  empirically  employed, 
did  not  materially  differ  in  principle  from  those  in  use  at  the  present 
day.  Thus  in  Strabo's  time  the  gold  was  placed  on  the  fire  with  three 
times  its  weight  of  salt  and  a  quantity  of  argillaceous  rock,  which  in  the 
presence  of  moisture  effected  the  decomposition  of  the  salt.  Hydrochloric 
acid  is  thus  formed,  which,  at  the  high  temperature  employed,  furnishes 
chlorine  to  the  silver  associated  with  the  gold,  which  is  converted  into  a 
chloride.     A  similar  process  is  still  practised  in  South  America. 

Among  other  methods  for  the  separation  of  gold  from  silver  or  other 
contaminating  metals  which  have  been  in  use  from  a  remote  period  may 
be  mentioned  prolonged  oxidation  by  exposure  to  air  and  melting  with 
sulphur,  sulphide  of  antimony,  and  corrosive  sublimate. 

The  "  quartation  "  process  of  refining — so  called  from  the  fact  that 
an  alloy  is  formed  which  contains  3  parts  of  silver  and  1  of  gold — con- 
sists in  first  forming  an  alloy  of  the  gold  with  silver  in  the  propor- 
tions given.  These  are  melted  to  ensure  homogeneity,  and  granulated  by 
pouring  into  water  contained  in  a  wooden  vessel.  The  pieces  are  then 
collected  and  placed  in  a  glass  or  platinum  vessel  and  acted  upon  by 
either  nitric  or  sulphuric  acid.  When  the  presence  of  lead  or  tin  is  sus- 
pected, this  should  be  got  rid  of  before  subjecting  the  alloy  to  the  acid ; 
otherwise  the  platinum  digester  would  be  injured.  The  removal  of  lead 
is  accomplished  by  cupelling  the  alloy,  while  tin  may  be  effectually  re- 
moved by  fusing   the    alloy   with   potassium   nitrate.     On  account  of 


GOLD.  97 

greater  economy  and  the  closeness  with  which  it  will  act  upon  silver 
containing  very  small  quantities  of  gold,  sulphuric  acid  is  at  the  present 
day  the  agent  most  commonly  employed,  particularly  where  large  quan- 
tities of  the  alloy  are  to  be  treated. 

The  nitric-acid  plan  does  not,  as  a  rule,  yield  gold  of  as  high  a 
degree  of  fineness  as  the  sulphuric-acid  treatment,  but  the  oxidizing 
property  of  the  nitric  acid  is  of  great  advantage  in  refining  gold  con- 
taminated with  antimony  and  other  equally  injurious  metals. 

When  nitric  acid  is  employed,  each  ounce  of  the  granulated  alloy  is 
treated  with  an  ounce  and  a  quarter  of  nitric  acid  of  specific  gravity 
1.32. 

The  sulphuric-acid  process  is  based  upon  the  fact  that  the  concen- 
trated hot  acid  converts  silver  and  copper  into  soluble  sulphates  without 
attacking  the  gold,  the  metallic  silver  being  recovered  from  the  sulphate 
in  the  form  of  needle-like  crystals  by  thrusting  copper  plates  ^  into  it. 
The  sulphate  of  copper  resulting  from  the  reaction  is  crystallized  and 
becomes  an  article  of  commerce.  The  sulphuric  acid  should  be  of  spe- 
cific gravity  1.84,  and  the  alloy  is  boiled  for  three  or  four  hours  in  a 
platinum  vessel  with  2.5  times  its  weight  of  acid.  The  sulphurous-acid 
fumes  which  arise  are  partially  condensed  before  being  allowed  to  pass 
into  the  air.  When  the  acid  has  ceased  to  act  upon  the  metal  a  small 
quantity  of  sulphuric  acid  of  specific  gravity  1 .53  is  added,  and  after  a 
second  boiling  the  contents  of  the  vessel  are  allowed  to  settle  :  the  liquid 
is  withdrawn  from  the  gold,  which  rests  at  the  bottom  of  the  vessel,  and 
is  diluted  until  its  density  is  1.21  to  1.26.  The  gold  is  then  carefully 
washed  and  melted  into  ingots,  which  generally  contain  from  997  to  998 
parts  of  gold  in  the  1000. 

In  the  nitric-acid  process  the  supernatant  liquid  consists  mainly  of 
argentic  nitrate.  The  silver  may  be  recovered  by  precipitation  with 
chloride  of  sodium,  argentic  chloride  resulting,  which  in  turn  is  exposed 
to  a  current  of  hydrogen,  liberating  metallic  silver." 

The  dry  method  of  refining  gold  before  alluded  to  consists  in  placing 
the  granulated  alloy  and  a  mixture  of  1  part  of  chloride  of  sodium  and 
2  parts  of  brick-dust  in  alternate  layers  in  a  crucible  until  the  latter  is 
full,  when  it  is  covered  and  placed  in  a  wood  fire  and  kept  at  a  dull  red- 
ness for  twenty-four  hours.  By  the  united  action  of  the  moisture  fur- 
nished by  the  wood  and  the  silica  of  the  brick-dust  the  sodic  chloride  is 
decomposed  ;  its  sodium  combines  with  oxygen  from  the  decomposition 
of  the  water,  forming  soda,  which  in  turn  unites  with  silica  to  form  sodic 
silicate.  The  hydrogen  of  the  water  and  the  liberated  chlorine  form 
hydrochloric  acid  :  these  at  the  temperature  at  which  the  operation  must 
be  carried  on  furnish  chlorine  to  the  silver,  converting  it  into  argentic 
chloride.  The  latter,  being  fusible,  is  absorbed  by  the  brick-dust,  per- 
mitting the  alloy  to  be  further  acted  upon  until  nearly  all  the  silver  is 
converted  into  chloride,  the  gold  remaining  comparatively  fine. 

There  is  also  another  cementation  process  given  ^  for  the  purpose  of 
acting  upon  the  surface  of  gold  containing  a  large  percentage  of  silver, 
by  which  means  it  is  made  to  resemble  fine  gold.  It  consists  in  subject- 
ing the  alloy,  previously  rolled  thin  and  covered  by  the  cement-powder, 

'  Iron  plates  are  sometimes  used.  ^  See  chapter  on  "Silver." 

^  This  process  is  attributed  to  Kerl,  and  is  described  in  Makins's  Metallurgy,  p.  224. 

7 


98  METALS  AND  ALLOYS. 

to  a  temperature  slightly  below  its  melting-point.  In  this  operation  the 
mixture  is  composed  of  1  part  of  sodic  chloride,  1  part  of  alum,  1  part 
of  ferrous  sulphate,  and  3  of  brick-dust.  At  the  high  temperature  nec- 
essary the  sulphates  are  decomposed,  with  liberation  of  free  sulphuric 
acid,  while  chlorine  is  evolved  from  the  sodic  chloride.  These  act  upon 
the  silver,  which  is  subsequently  found  in  the  cement-powder  in  the 
form  of  argentic  chloride. 

Refining  by  chlorine  gas,  devised  by  F.  B.  Miller  of  Sydney, 
N.  S.  W.,  in  1867,  is  a  valuable  and  accurate  dry  method  for  separating 
silver  from  gold.  The  process  is  the  one  now  practised  in  the  Austra- 
lian mints,  where  it  has  been  quite  extensively  employed,  1,100,000 
ounces  of  gold  having  been  refined  by  it  in  Sydney  during  one  year, 
the  percentage  of  loss  during  the  operation  being  only  14  parts  in  the 
100,000.  It  consists  in  converting  the  silver  into  chloride  by  the  pas- 
sage of  a  stream  of  chlorine  gas  through  the  ipolten  alloy.  By  means 
of  a  clay  pipe  passing  through  the  cover  to  the  bottom  of  the  crucible, 
and  connected  with  the  chlorine-generator  by  means  of  a  flexible  tube, 
the  gas  is  passed  rapidly  through  the  melted  metal,  and  is  apparently 
absorbed  by  it.  The  refining  is  considered  as  complete  when  orange- 
colored  fumes  begin  to  rise.  As  soon  as  this  evolution  of  gas  is  noticed 
the  crucible  should  be  removed  from  the  fire  to  prevent  the  gold  itself 
from  combining  with  the  chlorine.  The  chloride  of  silver,  which  is 
fusible,  should  be  poured  oif  from  the  surface  of  the  molten  metal,  and, 
if  it  retains  a  small  portion  of  the  gold,  this  may  be  recovered  by  fusing 
with  a  little  carbonate  of  soda,  which  causes  the  gold  to  separate  and 
settle  to  the  bottom  of  the  crucible.  This  method  is  capable  of  produ- 
cing gold  of  from  944  to  1000  fine. 

The  gold  is  next  melted  into  bars,  and  the  argentic  chloride  is  reduced 
to  metallic  silver  by  placing  it  between  two  wrought-iron  plates,  and 
then  immersing  the  whole  in  a  vessel  of  water  acidulated  Avith  sulphuric 
acid,  when,  after  a  few  hours,  the  silver  will  all  be  reduced.  It  generally, 
however,  contains  a  small  percentage  of  gold,  which  may  be  recovered 
either  by  again  dissolving  the  silver  with  nitric  acid,  when  the  gold  will 
be  found  at  the  bottom  of  the  vessel,  or  it  may  be  separated  by  fusing 
the  argentic  chloride,  to  which  is  added  a  small  quantity  of  potassic 
carbonate  for  the  purpose  of  reducing  a  little  metallic  silver.  The  latter 
in  subsiding  through  the  argentic  chloride  reduces  the  gold,  which  has 
probably  combined  with  the  chlorine.  While  yet  hot  and  in  a  fluid  state 
the  argentic  chloride  is  poured  off  and  reduced  as  before,  when  it  will  be 
found  free  of  gold.  The  little  button  which  subsides  to  the  bottom  of 
the  vessel  will  be  found  to  consist  of  gold,  the  reduced  silver,  and  some 
argentic  chloride.  The  latter  must  be  again  decomposed  by  fusing  with 
potassic  carbonate.  Theoretically,  1  cubic  foot  of  chlorine  will  convert 
S\  ounces  of  silver  into  argentic  chloride,  but  in  practice  about  twice 
that  quantity  is  required.  Thus  far,  the  use  of  chlorine  for  refining  upon 
a  large  scale  has  proved  to  be  much  more  economical  and  expeditious 
than  the  humid  process,  the  time  required  to  part  300  ounces  in  1  fur- 
nace being  about  two  hours,  and  the  average  cost  4  cents  per  ounce. 

Treatment  of  Brittle  Gold. — The  slightest  admixture  of  such  metals 
as  arsenic,  antimony,  tin,  lead,  etc.  is  sufficient  to  seriously  impair  the 
ductility  of  gold,  and  the  metal  will  require  to  be  exposed  while  in  a 


GOLD.  99 

state  of  fusion  to  a  stream  of  chlorine  gas,  which  removes  the  deleterious 
substances  by  converting  them  into  volatile  chlorides.  The  toughness 
of  gold  may  also  be  restored  by  throwing  a  small  quantity  of  corrosive 
sublimate  on  the  surface  of  the  molten  metal,  the  vapor  of  which  con- 
'' verts  the  metallic  impurities  into  chloride.  In  the  dental  laboratory 
gold  is  liable  to  become  contaminated  with  small  particles  of  lead  or 
zinc.  These  may  be  effectually  removed  by  melting  with  a  mixture  of 
potassium  nitrate  and  borax,  when  the  foreign  metals  will  be  oxidized 
and  dissolved  in  the  slag. 

The  gold  of  this  country  is  often  found  to  contain  iridium,  the  pres- 
ence of  which  greatly  impairs  the  metal  for  coinage  and  other  purposes. 
The  little  hard  grains  occasionally  met  with  in  gold,  upon  which  the  file 
makes  no  impression,  consist  of  iridium  or  a  native  alloy  of  osmium 
and  iridium  ;  they  are  not  combined  with  the  gold,  but  merely  dissem- 
inated through  it.  The  only  dry  method  of  separating  iridium  from 
gold  consists  in  alloying  the  latter  with  three  times  its  weight  of  silver, 
by  which  means  the  specific  gravity  of  the  metal  is  so  much  lowered 
that  the  iridium,  which  is  very  infusible  and  of  a  specific  gravity  of 
21.1,  will  subside  to  the  bottom  of  the  crucible,  when  the  gold  and 
silver  alloy  may  be  poured  or  ladled  off.  As  some  gold  will  remain 
with  the  residue,  more  silver  must  be  melted  with  it,  the  operation  being 
repeated  several  times  until  all  the  gold  is  removed.  What  is  left  is  then 
acted  upon  by  sulphuric  acid  to  dissolve  the  silver,  when  the  iridium 
and  some  finely-divided  gold  will  be  left.  These  may  be  separated  by 
washing. 

Iridium  may  also  be  separated  from  gold  by  the  wet  process.  The 
gold  is  melted  with  three  times  its  weight  of  silver,  and  granulated  to 
ensure  admixture.  The  alloy  is  then  treated  with  nitric  acid,  which 
dissolves  the  silver,  leaving  the  gold  and  iridium  at  the  bottom  of  the 
vessel.  The  gold  may  now  be  acted  upon  by  nitro-hydrochloric  acid. 
The  iridium  may  then  be  collected  and  washed  to  free  it  from  any  por- 
tion of  the  gold.  The  latter  may  be  recovered  from  its  solution  by 
precipitation,  oxalic  acid  or  sulphurous  acid  being  usually  employed. 

Preparation  of  Chemically-pure  Gold. — None  of  the  methods  which 
have  been  described  can  always  be  relied  upon  to  afford  absolutely  pure 
gold.  When  nitric  acid  is  employed  in  the  quartation  process  gold  may 
be  obtained  from  993  to  997  parts  in  the  1000,  while  sulphuric  acid  will 
yield  gold  up  to  998  thousandths. 

There  are  several  methods  by  which  chemically-pure  gold  may  be 
obtained.  Usually,  ordinary  refined  gold,  obtained  by  one  of  the 
methods  above  described,  is  dissolved  in  nitro-hydrochloric  acid.  The 
excess  of  acid  is  driven  off,  and  alcohol  and  chloride  of  potassium  are 
added  for  the  purpose  of  precipitating  platinum  if  any  is  present.  The 
chloride  of  gold  is  then  dissolved  in  pure  distilled  water  until  each 
gallon  does  not  contain  more  than  half  an  ounce  of  the  chloride.  Any 
silver  present  will  be  converted  into  argentic  chloride,  which  will  settle 
to  the  bottom  of  the  vessel,  after  which  the  supernatant  liquid  should  be 
carefully  removed  by  means  of  a  siphon.  The  gold  may  be  precipitated 
by  a  stream  of  carefully- washed  sulphurous  anhydride  or  by  the  addi- 
tion of  oxalic  acid.  The  precipitated  metal  is  washed  with  dilute  hydro- 
chloric acid,  distilled  water,  ammonia-water,  and  again  with  distilled 


100  METALS  AND  ALLOYS. 

water,  and  is  then  ready  for  melting.  This  is  done  in  a  clay  crucible 
with  a  small  portion  of  bisulphate  of  potash  and  borax.  The  melted 
metal  should  be  poured  into  a  stone  ingot-mould.  By  this  method  gold 
of  which  the  purity  was  999.96  has  been  prepared,  the  precipitant  being 
oxalic  acid  ;  but  gold  precipitated  by  that  agent  from  an  acid  solution 
containing  copper  is  always  contaminated  with  cupric  oxalate,  to  avoid 
which  the  solution  should  be  heated  with  the  addition  of  potash,  when  a 
soluble  double  oxalate  of  copper  and  potash  is  formed,  leaving  the  gold 
in  the  pure  state. 

The  aqua  regia  used  in  the  preparation  of  chemically-pure  gold  should 
consist  of  2  parts  of  hydrochloric  and  1  part  of  nitric  acid.  The  specific 
gravity  of  the  former  should  be  about  1.16,  and  of  the  latter  1.45.  Each 
ounce  of  gold  will  require  for  its  solution  about  3^  ounces  of  the  mixed 
acids.  The  action  of  this  upon  the  metal  will  in  the  beginning  be  quite 
energetic,  but  as  the  solution  approaches  saturation  the  application  of 
moderate  heat  is  required  to  dissolve  the  last  portion  of  the  gold.  The 
greatest  care  must  be  exercised  in  the  separation  of  the  gold  solution 
from  the  argentic  chloride,  which  subsides  to  the  bottom  of  the  vessel, 
and  also  to  rid  the  liquid  of  the  small  portion  of  silver  held  in  solution 
by  the  acid.  The  solution  is  cautiously  transferred  to  an  evaporating 
dish  by  means  of  a  siphon  and  heat  is  applied,  and,  as  the  bulk  is  gradu- 
ally reduced  by  evaporation,  more  argentic  chloride  wnll  be  separated  and 
deposited  at  the  bottom.  The  supernatant  liquid  should  again  be  care- 
fully poured  or  siphoned  off',  and  this  should  be  repeated  as  often  as  the 
residue  appears  in  the  dish.  When  the  solution  has  become  viscid  and 
of  a  deep-ruby  color  the  heat  is  discontinued,  and  the  auric  chloride  soon 
crystallizes  in  a  mass  of  prismatic  forms.  It  should  then  be  dissolved 
and  largely  diluted  with  distilled  Avater,  acidulated  by  a  few  drops  of 
hydrochloric  acid,  and,  after  standing  for  a  few  days  to  permit  a  further 
subsidence  of  argentic  chloride,  it  should  be  filtered,  when  it  is  ready  for 
precipitation.  This  may  be  accomplished  by  quite  a  number  of  different 
reagents,  but  the  form  of  the  precipitated  metal  depends  upon  the  nature 
of  the  precipitant,  and  it  may  be  thrown  down  in  a  spongy  condition, 
in  sheets  resembling  foil,  as  a  powder,  in  a  more  or  less  crystalline  state, 
and  in  scales.  The  affinity  of  gold  for  other  bodies  is  so  weak  that  care 
must  be  observed  lest  partial  reduction  be  effected  by  merely  adventitious 
conditions.  The  highly  diluted  neutral  solution  of  the  trichloride  just 
described  is  quite  liable  to  such  accidents ;  indeed,  it  may  occur  from 
exposure  to  air,  atmospheric  nitrogen  probably  being  the  active  agent. 
The  addition  of  pure  water  to  such  a  solution  may  also  cause  slight  pre- 
cipitation, but  the  dilute  solution  may  be  protected  from  premature  pre- 
cipitation by  acidulation  with  a  small  quantity  of  hydrochloric  acid. 

The  best  agents  for  the  precipitation  of  gold  are  oxalic  acid,  sulphurous 
acid,  and  ferrous  sulphate.  Oxalic  acid  will  precipitate  several  forms  of 
gold,  from  sponge-like  masses  to  the  different  crystalline  or  powdery 
forms.  Its  action  is,  however,  slower  than  the  others,  and  it  requires  to 
be  slightly  heated.     The  reaction  is  shown  in  the  following  equation  : 

2AUCI3  +  SH^O,  =  6HC1  +  6CO2  +  2Au. 

The  chlorine  of  the  auric  chloride  unites  with  the  hydrogen  of  the 
oxalic  acid  to  form  hydrochloric  acid,  the  copious  evolution  of  gas  noticed 


GOLD.  101 

during  the  precipitation  being  the  escape  of  the  carbonic  acid  formed  by 
the  remaining  elements  of  the  oxalic  acid.     The  gold  is  thus  set  free. 

The  so-called  "  shredded  gold/'  somewhat  extensively  used  by  dentists 
in  filling  teeth  in  1867-68,  was  produced  by  the  addition  of  sugar  or 
gum  arabic  to  an  acid  solution  of  gold.  The  exact  modus  operandi  is  as 
follows :  The  pure  gold  is  dissolved  in  nitro-hydrochloric  acid,  and, 
without  evaporating  the  solution,  it  is  diluted  by  the  addition  of  about 
two-thirds  its  bulk  of  pure  water.  Clean  gum  arabic,  dissolved  in  boiling 
water,  to  the  amount  of  one-third  the  bulk  of  the  gold  solution  is  added 
to  the  latter,  and  the  whole  poured  into  a  glass  matrass  or  evaporating- 
dish  and  placed  over  a  steam  bath.  When  the  proper  temperature  is 
attained  gold  in  the  form  of  leaves,  shreds,  or  fibres  will  be  observed 
floating  in  the  liquid.  When  these  become  sufficiently  coherent  to  admit 
of  removal,  they  are  lifted  out  by  a  vulcanized  rubber  spoon  attached  to 
a  glass  rod  and  placed  in  a  filter.  This  operation  is  continued  until  the 
gum  arabic  or  sugar,  assisted  by  heat,  has  caused  the  precipitation  of  all 
the  gold  held  in  solution.  The  web-like  masses  are  then  thoroughly 
washed,  dried,  and  heated  to  dull  redness.  As  the  elements  entering 
into  the  composition  of  sugar  and  gum  arabic  are  identical  with  those  of 
oxalic  acid,  the  reaction  is  probably  the  same  as  that  which  occurs  when 
the  latter  is  employed  as  the  precipitant.  With  care  in  the  application 
of  the  proper  amount  of  heat  the  action  of  precipitants  of  this  class  is 
capable  of  regulation,  thus  affi)rding  uniform  results. 

When  the  precipitated  gold  is  intended  for  plate  or  bars,  it  should  be 
well  washed,  and  fused  in  a  perfectly  new  crucible. 

Sulphurous  acid  precipitates  gold  generally  in  the  form  of  a  scaly 
metallic  powder ;  hence  it  does  not  affiard  masses  sufficiently  coherent  or 
sponge-like  for  use  as  a  filling  material  for  the  dentist.  The  reaction 
which  takes  place  is  thus  explained  : 

2AUCI3  +  H,0  +  3H2SO3  =  6HC1  +  3H3SO,  +  2Au. 

The  water  present  is  decomposed,  its  hydrogen  uniting  with  the 
chlorine  of  the  auric  chloride  to  form  hydrochloric  acid.  The  oxygen 
of  the  water,  attracted  to  the  sulphuric  acid,  converts  it  into  sulphuric 
acid,  and  the  gold  is  thus  liberated. 

Ferrous  sulphate  precipitates  gold  in  the  form  of  a  light-brown 
powder.  Of  the  sulphate  crystals  about  four  times  the  weight  of  the 
gold  is  dissolved  in  water.  This  is  added  to  the  auric  solution.  After 
the  finely-divided  gold  has  entirely  subsided  it  should  be  boiled  several 
times  in  dilute  hydrochloric  acid,  in  order  to  free  it  from  all  traces  of 
the  iron  with  which  it  is  liable  to  be  contaminated.  The  interchange, 
which  in  this  reaction  results  in  the  liberation  of  the  gold,  is  expressed 
by  the  following  equation  : 

2AUCI3  +  6FeSO,  =  Fe^Clg  +  2(Fe33S04)  +  2Au. 

The  ferrous  salt  parts  with  a  portion  of  the  iron  to  the  chlorine  of  the 
gold  salt,  thus  forming  ferric  chloride  and  ferric  sulphate,  while  the  gold 
is  liberated. 

As  stated  before,  the  reduction  of  the  metal  from  the  trichloride  may 
be  effiicted  (in,  however,  a  less  satisfactory  manner)  by  many  different 
reagents,  some  of  which  are  purely  elementary.    Thus,  sulphurj  selenium. 


102  METALS  AND  ALLOYS. 

carbon  (charcoal),  and  phosphorus,  each,  when  introduced  into  a  heated 
solution,  becomes  coated  with  a  film  of  metallic  gold.  Reduction  may 
also  be  accomplished  by  some  of  the  gaseous  bodies  containing  hydro- 
gen. Thus,  gold  may  be  precipitated  by  arseniuretted  and  antimoni- 
uretted  hydrogen.  Many  of  the  base  metals,  such  as  bismuth,  zinc,  etc., 
also  reduce  gold  from  solution  in  the  form  of  a  brown  powder.  It  is 
also  reduced  on  a  platinum  pole  by  the  electrical  current.  In  this  way 
the  beautiful  form  of  gold  made  by  A.  J.  Watts  of  New  York  is  pro- 
duced. In  a  solution  of  auric  chloride  plates  of  pure  gold  are  suspended. 
These  are  connected  with  a  battery,  so  that  as  the  solution  loses  its  gold 
by  deposition  of  the  metal  it  is  resupplied  from  the  suspended  plates. 
By  this  means  large  masses  of  perfectly  pure  crystal  gold  may  be 
obtained. 

Gold  may  also  be  precipitated  by  some  of  the  metallic  salts,  of  which 
nitrate  of  mercury  and  chloride  of  antimony  may  be  named  as  examples. 
Quite  a  number  of  organic  substances  will  also  precipitate  it,  a  promi- 
nent example  of  which  is  gallic  acid.  The  tartrate,  citrate,  and  acetate 
of  potassium  will  also  reduce  it.  Some  of  the  members  of  this  class, 
however,  require  the  addition  of  heat,  and  to  obtain  prompt  action  with 
these  agents  the  solution  should  be  quite  neutral. 

Alloys  of  Gold. — The  most  important  alloys  are  those  with  silver 
and  copper.  The  coinage  of  the  present  day,  from  which  the  dentist 
usually  obtains  his  plate,  is  mainly  an  alloy  of  gold  and  copper  in  the 
proportion  of  900  parts  of  gold  in  1000. 

Alloys  of  gold  for  bases  for  artificial  dentures  should  be  of  such  fine- 
ness as  will  enable  them  to  resist  the  chemical  action  of  the  fluids  of  the 
mouth,  while  at  the  same  time  they  should  possess  the  requisite  hardness, 
strength,  and  elasticity.  These  properties  are  usually  conferred  by  the 
addition  of  copper  and  silver  or  either  of  these  metals  singly,  or  by 
copper,  silver,  and  platinum.  The  quality  of  gold  which  is  to  be  intro- 
duced into  the  mouth  should,  as  a  rule,  be  of  a  standard  of  fineness  not 
less  than  18  carats.  Care,  however,  should  be  observed  in  remelting  the 
scraps  and  filings  of  the  drawer  that  the  grade  of  the  gold  be  not  lowered 
by  the  admixture  of  gold  plates,  backings,  etc.  containing  portions  of 
solder.  Indeed,  much  the  safer  rule  is  to  remelt  only  new  scraps  on 
which  no  solder  has  been  used.  The  scraps  and  filings  of  doubtful 
quality  may  be  sent  to  the  mint  for  coinage,  the  charge  for  which,  on 
the  hundred  dollars  (the  minimum  amount  received  by  tlie  United  States 
Mint)  is  less  than  1  per  cent. 

Gold  exceeding  1 9  carats  in  fineness  will  generally  be  found  too  soft 
and  yielding  for  use  in  the  mouth.  The  amount  of  force  which  the 
plate  must  sustain  in  mastication  is  much  greater  than  might  be  sup- 
posed ;  hence,  if  the  degree  of  purity  of  the  alloy  be  too  high,  the 
requisite  amount  of  rigidity  and  strength  will  be  wanting,  and  the  plate 
will  soon  bend  to  such  an  extent  that  it  will  no  longer  fit  the  mouth. 
This  difficulty  may,  however,  be  avoided  in  the  higher  grades  of  gold 
plate  intended  for  dental  purposes  by  a  slight  admixture  of  platinum, 
by  which  much  greater  tenacity  is  obtained ;  otherwise,  the  plate  will 
require  strengthening  by  doubling  at  such  points  as  are  most  liable  to 
bend.  Plates  for  partial  cases  necessarily  require  a  great  deal  of 
strengthening.     This  adds  considerably  to  the  expenditure  of  time  and 


GOLD. 


103 


labor  in  the  construction  of  the  plate.  It  increases  its  weight,  and  does 
not  always  render  the  plate  sufficiently  rigid  to  withstand  the  force  of 
mastication. 

Gold  plate  suitable  for  dental  purposes  may  be  prepared  according  to 
the  following  formulae  : 


Gold  Plate  18   Carats  Fine. 


No.  1. 

Pure  Gold IS  dwt. 

Pure  Copper 4    " 


No.  2. 


Pure  Silver 2 

Gold  Plate  19   Carats  Fine. 


Gold  Coin 20dwt, 

Pure  Copper 2    " 

Pure  Silver 2    " 


No.  3. 

Pure  Gold 19  dwt. 

Pure  Copper 3    " 

Pure  Silver 2    " 


Pure  Silver 
Gold  Plate  20  Carats  Fine. 


No.  4. 

Gold  Coin 20  dwt. 

Pure  Copper    .        25      gr. 

..•••...  40+  " 


No.  5. 

Pure  Gold 20  dwt. 

Pure  Copper 2    " 

Pure  Silver 2    " 


No.  6. 

Gold  Coin 20  dwt. 

Pure  Copper 18      gr. 

Pure  Silver 20  +  " 


Gold  Plate  '21   Carats  Fine. 


No.  7. 

Pure  Gold 21  dwt. 

Pure  Copper 2    " 

Pure  Silver 1    " 


No.  8. 

Gold  Coin 20  dwt. 

Pure  Silver 13  -f  gr. 


No.  9. 

Gold  Coin 20  dwt. 

Pure  Copper 6  gr. 

Pure  Platinum 7§  " 


Gold  Plate  22   Carats  Fine. 

No.  10. 

Pure  Gold 22  dwt. 

Fine  Copper 1    " 

Pure  Silver 18  gr. 

Pure  Platinum 6    " 

Gold  Plate  18   Carats  Fine. 

No.  11. 

United  States  Gold  Coin  ($60) 64J  dwt. 

Pure  Silver 13      " 

On  account  of  its  greater  strength  and  power  of  resisting  the  chemi- 
cal action  of  the  fluids  of  the  mouth  many  dentists  prefer  to  use  gold 
plate  20  or  21  carats  fine,  in  which  the  reducing  constituents  are  cop- 
per and  platinum,  the  following  formula  being  an  example  : 


104  METALS  AND  ALLOYS. 

Gold  Coin 20  dwt. 

Pure  Platinum 10  gr. 

The  union  of  platinum  with  gold  yields  an  alloy  possessing  great 
strength  and  considerable  elasticity.  Such  an  admixture,  however,  has 
its  disadvantages.  Owing  to  its  increased  strength  and  stiffness  a  much 
thinner  and  lighter  plate  may  be  employed  without  the  additional  labor 
and  cost  of  doubling  the  plate  at  what  in  partial  cases  composed  of 
ordinary  18-,  19,-  or  20-carat  gold  would  be  weak  points.  It  may  also 
be  justly  claimed  for  gold  alloyed  with  platinum  that  it  will  perfectly 
resist  the  action  of  the  fluids  of  the  mouth.  On  the  other  hand,  the 
richness  of  color  of  the  gold  is  always  more  or  less  impaired  by  the  ad- 
mixture of  platinum.  But  perhaps  the  greatest  objection  to  be  urged 
against  the  employment  of  platinous-gold  is  the  increased  difficulty  of 
swaging  a  plate  composed  of  it  so  that  it  shall  perfectly  conform  to  all 
the  depressions  and  irregularities  of  the  model.  Having  invariably 
found,  when  the  alloy  contained  any  considerable  percentage  of  platinum, 
that  the  ordinary  method  of  swaging  between  zinc  and  lead  was  not 
effective,  the  author  has  for  more  than  twenty  years  employed  zinc  for 
counter-dies  as  well  as  for  dies  :  this  entirely  overcomes  any  difficulty  in 
swaging.^ 

Gold  for  use  in  the  formation  of  clasps  should  always  contain  suf- 
ficient platinum  to  render  it  much  more  elastic  than  the  alloys  usually 
employed  in  the  plate  or  base,  so  that  on  the  application  of  force  upon 
the  denture  in  the  act  of  mastication  the  clasp,  though  it  may  yield 
slightly,  will  always  spring  together  again  and  accurately  embrace  the 
tooth  which  it  surrounds.  In  the  perfect  adjustment  of  clasps  to  re- 
maining teeth  the  following  points  are  of  importance  :  First,  the  model 
must  be  as  accurate  as  a  plaster  impression  will  afford ;  second,  the  clasp 
should  be  thrown  around  the  thickest  or  most  prominent  part  of  the 
tooth ;  third,  the  clasp  should  be  so  arranged  as  to  fit  accurately  the 
convexity  of  the  tooth.  To  successfully  accomplish  this  the  gold,  of 
about  No.  26  of  the  standard  gauge,  should  be  cut  by  pattern,  and  before 
any  attempt  is  made  to  fit  it  to  the  tooth  it  should  be  bent  with  the 
clasp-benders  to  correspond  with  the  rounded  surfaces  of  the  natural 
tooth.  Lastly,  the  contact  of  the  clasps  Avith  the  tooth  should  be  uni- 
form. The  ends  of  the  clasp  should  be  free,  and  it  should  be  attached 
to  the  plate  at  one  point,  so  that  but  little  of  its  circumference  shall  be 
included  in  the  union ;  otherwise  if  a  large  proportion  of  the  clasp  be 
soldered  fast  to  the  plate,  much  of  the  quality  of  elasticity  will  be 
lost. 

The  following  formulae  will  afford  alloys  of  20-carat  fineness  suit- 
able for  clasps,  backings,  hard  wire  for  crown-posts,  spring  wire,  and 
wherever  elasticity  and  additional  strength  are  required : 


Formula  No.  1. 

Pure  Gold 20  dwt. 

Pure  Copper 2     " 

Pure  Silver 1     " 

Pure  Platinum 1     " 


Formula  No.  2. 

Coin  Gold 20  dwt. 

Pure  Copper 8  gr. 

Pure  Silver      10  " 

Pure  Platinum 20  " 


^  See  chapter  on  "  Zinc." 


GOLD. 


105 


Alloys  of  Gold  employed  in  Dentistry  as  Solders. — These  are  a  class 
of  alloys  formed  of  the  metal  to  be  united,  the  fusing-point  of  which  is 
reduced  by  the  addition  of  silver,  copper,  and  brass  : 


No.  1,  14-  Carats  Fine. 

Pure  Silver 2J  dwt. 

Pure  Copper 20    gr. 

Pure  Zinc 35     " 

18-carat  Gold  Plate  (Formula  No. 

11) 20    dwt. 


No.  2,  15  Carats  Fine. 

Gold  Coin 6  dwt. 

Pure  Silver 30  gr. 

Pure  Copper 20  " 

Brass 10  " 


No.  3,  16  Carats  Fine. 

Pure  Gold 11  dwt.  12  gr. 

Pure  Silver 3     " 

Pure  Copper 1     "     12  " 

Pure  Zinc 12  " 


No.  4;  18  Carats  Fine. 


Gold  Coin 30  parts. 

Pure  Silver 4     " 

Pure  Copper      1  part. 

Brass 1     " 


No.  5,  20  Carats  Fine,  for  Crown- 
and  Bridge-work. 

American  Gold  Coin  (21.6  carats 

fine),  $10  piece 258  gr. 

Spelter  Solder 20.64  " 


No.  6,  20  Carats  Fine,  same  Use  as  No.  5. 

Pure  Gold 5  dwt. 

Pure  Copper 6  gr. 

Pure  Silver 12  " 

Spelter  Solder 6  '' 

No.  7,  20  Carats  Fine,  for  Crown-  and  Bridge-ivork. 

Zinc 11  gr. 

Pure  Gold 20     " 

Silver  Solder 3    " 

No.  8,  Dr.  C.  M.  Richmond's  Solder  for  Bridge-work. 

Gold  Coin 5  dwt. 

Fine  Brass  Wire 1     " 

No.  9,  Dr.  Low's  Formula  for  Solder  in  Crown-  and  Bridge-work,  19 

Carats  Fine. 

Coin  Gold 1  dwt. 

Copper 2  gr. 

Silver 4   " 

Dr.  W.  H.  Dorrance  prepares  an  alloy  of — 

Pure  Silver 1  dwt. 

Pure  Zinc 2     " 

Pure  Copper 3     " 

With  this  alloy  he  forms  the  different  grades  of  gold  solders.  To  form 
a  solder  suitable  for  bridge-work,  of  20  carats  fine,  he  melts  4  grains  of 
the  alloy  with  20  grains  of  pure  gold. 

Spelter  solder,  composed  of  equal  parts  of  copper  and  zinc,  is  some- 
times employed  as  a  constituent  in  the  preparation  of  gold  solders  for 


106  METALS  AND  ALLOYS. 

the  purpose  of  reducing  the  fusing-point.  Thus  some  dentists  use  an 
alloy  composed  of — 

18-carat  Gold 6  dwt. 

Granulated  Spelter  Solder 6  gr. 

An  alloy  of  this  composition  is  exceedingly  brittle,  and  hence  difficult  to 
roll  into  plate  without  breaking  into  many  pieces.  Its  color  is  good,  but 
the  author  has  noticed  that  the  surface  of  such  solders,  after  flowing,  is 
apt  to  be  pitted  with  small  holes  and  has  not  the  solid  and  uniform 
appearance  that  is  desirable.  This  may  be  due  to  the  oxidation  and 
escape  of  some  of  the  zinc. 

Methods  of  Reducing  Gold  to  a  Lower  or  Higher  Standard  of  Fineness^ 
and  of  Determining  the  Carat  of  any  Given  Alloy. — The  gold  alloys  used 
in  the  laboratory  are  generally  made  from  pure  gold  or  gold  coin,  the 
standards  of  which  are  definitely  fixed.  A  few  simple  rules  are  here 
given  by  which  the  operator  may  readily  determine  the  quality  of  alloy 
necessary  to  reduce  either  coin  or  pure  gold  to  any  desired  standard. 

To  ascertain  the  carat  of  any  given  alloy  multiply  24  by  the  weight 
of  gold  in  the  alloyed  mass,  and  divide  the  product  by  the  weight  of  the 
mass.  The  quotient  is  the  carat  sought.  For  example,  take  the  following : 

Pure  Gold 18  parts. 

Copper 4     " 

Silver 2     " 

24  parts. 
The  result  may  be  thus  expressed  : 

24  X  18-24  =  18  carats. 

To  reduce  gold  to  a  required  carat  multiply  the  weight  of  gold  used 
by  24,  and  divide  the  product  by  the  required  carat.  The  quotient  is 
the  weight  of  the  mass  when  reduced,  from  which  subtract  the  weight  of 
gold  used,  and  the  remainder  is  the  weight  of  the  alloy  to  be  added. 

To  raise  gold  from  a  lower  to  a  higher  carat  multiply  the  weight  of 
the  alloyed  gold  used  by  the  number  representing  the  proportion  of  alloy 
in  the  given  carat ;  divide  the  product  by  the  figures  representing  the 
quantity  of  alloy  in  the  required  carat.  The  quotient  is  the  weight  of 
the  mass  when  reduced  to  the  required  carat  by  adding  fine  gold.  Thus, 
to  raise  1  pennyweight  of  16-carat  gold  to  18  carats  the  numbers  repre- 
senting the  proportions  of  alloys  are  obtained  by  subtracting  18  and  16 
from  24.     The  statement  is — 

6:8::  1:11; 

from  which  it  will  be  seen  that  to  raise  1  pennyweight  of  16-carat  gold  to 
18  carats  one-third  of  a  pennyweight  of  pure  gold  must  be  added  to  it. 

Again,  if  instead  of  using  pure  gold  we  desire  to  raise  the  fineness  of 
1  pennyweight  of  1 6-carat  gold  to  that  of  1 8  by  the  addition  of,  say,  22- 
carat  gold,  the  numbers  representing  the  proportions  of  the  alloy  would 
be  found  by  subtracting,  in  the  example  given,  16  and  18  from  22,  the 
result  being — 

4  : 6  :  :  1  :  11 

Hence  each  pennyweight  of  1 6-carat  gold  would  require  a  half  penny- 
weight of  22-carat  gold  to  raise  it  to  18  carats. 


GOLD. 


107 


The  fineness  of  gold  may  be  expressed  in  decimals  or  in  parts  called 
carats.  The  former  is  the  system  employed  at  the  United  States  Mint 
and  by  metallurgists  and  chemists,  while  the  latter  is  the  usual  method 
of  expressing  the  grade  of  alloys  of  gold  among  dentists  and  jewellers. 
The  following  table  will  show  the  relation  of  one  to  the  other : 


Pure  gold 

English  coin 

American  coin 

Dentists'  gold 

Jewellers'  gold,  best  .    .    . 

"  "    good     .    . 

"  "     low  grade 

Common  jewellers'  solder 


Carats. 

Decimals. 

24 

1000. 

22 

916.6 

21.6 

900. 

20 

833.3 

19.2 

800. 

18 

750. 

15 

625.  . 

12 

500. 

8 

333.3 

There  are  many  different  alloys  used  in  the  arts.  The  greenish  alloy 
used  by  jewellers  contains  70  per  cent,  of  silver  and  30  per  cent,  of  gold. 
"  Blue  gold "  is  stated  to  contain  75  per  cent,  of  iron.  The  Japanese 
employ  a  compound  of  gold  and  silver  the  standard  of  which  varies 
from  350  to  500.  This  alloy  is  exposed  to  the  action  of  a  mixture  of 
plum-juice,  vinegar^  and  sulphate  of  copper.  They  also  possess  a  num- 
ber of  bronzes  in  which  tin  and  zinc  are  replaced  by  gold  and  silver. 
The  alloy  known  as  shiya-ku-do,  extensively  used  for  sword-ornaments, 
contains  70  per  cent,  of  copper  and  30  per  cent,  of  gold. 

Alloys. — Gold  and  Silver. — The  density  of  those  natural  alloys 
the  composition  of  which  varies  from  AuAgg  to  AugAg  is  greater  than 
that  calculated  from  the  densities  of  the  constituent  metals.  Gold  and 
silver  unite  in  all  proportions,  affording  alloys  of  several  tints,  ranging 
from  the  color  of  silver  to  that  of  gold.  By  the  addition  of  silver  the 
hardness  of  gold  is  increased,  and  it  is  rendered  more  fusible,  while  its 
malleability  is  not  materially  diminished.  Gold  as  found  in  nature 
always  contains  silver,  and  all  specimens  of  native  silver  will  likewise 
be  found  to  contain  gold. 

Gold  and  Platinum. — Equal  weights  of  the  two  metals  yield  an  alloy 
of  good  malleability,  with,  however,  some  dulness  of  color.  An  excess 
of  platinum  renders  the  alloy  infusible  in  an  ordinary  blast-furnace. 
One  part  of  platinum  to  9.5  of  gold  will  afford  an  alloy  of  the  same 
density  as  platinum. 

Gold  and  Tin. — Alloys  of  tin  and  gold  are  hard  and  brittle,  and  the 
combination  is  attended  with  contraction.  Thus,  the  alloy  SnAu  has  a 
density  14.243,  instead  of  14.828,  as  indicated  by  calculation. 

Gold  and  Mercury. — These  combine  at  all  temperatures,  but  the 
union  may  be  greatly  facilitated  by  heating,  and  a  state  of  fine  division 
still  further  assists  the  process.  It  is  stated  that  an  amalgam  composed 
of  6  parts  of  mercury  to  1  of  gold  crystallizes  in  four-sided  prisms,  and 
that  if  the  mercury  is  then  distilled  off  the  gold  is  left  in  an  arborescent 
state.  The  operation  of  coating  the  surface  of  brass  or  copper  objects 
with  gold,  extensively  practised  some  years  ago  and  known  as  "  fire- 
gilding,"  was  based  upon  the  amalgamation  of  gold  and  mercury.     The 


108  METALS  AND  ALLOYS. 

process  is  as  follows  :  The  article  to  be  gilded  is  given  a  uniform  coating 
of  an  amalgam  made  by  heating  6  parts  of  mercury  with  1  part  of  gold, 
with  the  surplus  mercury  removed  by  squeezing.  The  operation  is 
greatly  facilitated  by  first  rubbing  the  surface  with  mercurous  nitrate. 
It  is  thus  given  a  superficial  layer  of  mercury.  It  is  now  gently  heated 
over  some  burning  charcoal,  the  amalgam  in  the  mean  time  being  kept 
uniformly  distributed  over  the  surface  by  means  of  a  soft  brush.  As 
the  heat  is  continued  and  the  mercury  is  gradually  driven  off  the  surface 
assumes  a  dull-yellow  color.  It  is  then  ready  for  polishing,  whicli  is 
accomplished  by  means  of  a  wheel-brush  moistened  with  vinegar. 
Verdigris  mixed  with  beeswax  is  applied  for  the  purpose  of  removing- 
any  remaining  mercury  by  means  of  the  affinity  which  the  latter  has 
for  the  acetate  of  copper.  This  operation,  sometimes  called  "  water- 
gilding,"  is  so  dangerous  to  health,  in  consequence  of  the  liability  of 
the  operator  to  inhale  the  volatilized  mercury,  that  it  has  been  almost 
entirely  superseded  by  electro-gilding. 

Gold  and  copper  yield  a  class  of  alloys  of  a  reddish  color  (between 
gold  and  copper)  which  are  much  harder  than  either  of  their  constituents. 
The  malleability  of  the  gold  is  not,  however,  much  affected  by  admix- 
ture of  copper,  provided  the  latter  is  pure.  It  is  stated  that  7  parts  of 
gold  with  1  of  copper  exhibit  the  greatest  degree  of  hardness  which  it 
is  possible  to  obtain  by  union  of  these  two  metals.  In  the  American 
coinage  the  alloy  is  chiefly  copper ;  hence  the  coins  are  red  in  color  and 
very  hard. 

Gold  and  Palladium. — These  metals  are  stated  to  alloy  in  all  pro- 
portions. Chenevix  states  that  an  alloy  composed  of  equal  parts  of  the 
two  metals  is  gray  in  color,  less  ductile  than  its  constituents,  and  has  the 
specific  gravity  of  11.08.  An  alloy  of  4  parts  of  gold  and  1  of  palla- 
dium is  white,  hard,  and  ductile.  According  to  Makins,  the  merest  trace 
of  palladium  with  gold  will  render  the  latter  very  brittle.  Graham  has 
shown  that  a  wire  of  palladium  alloyed  with  from  24  to  25  parts  of  gold 
does  not  exhibit  the  remarkable  retraction  which,  in  pure  palladium, 
attends  its  loss  of  occluded  hydrogen. 

Gold  and  Zinc. — It  appears  that  these  two  metals  possess  a  strong 
affinity  for  each  other,  but  all  the  alloys  of  zinc  and  gold  are  more 
or  less  brittle  according  to  the  quantity  of  zinc  present.  Care  should 
therefore  be  observed  in  the  dental  laboratory,  where  so  much  zinc  is 
employed,  that  small  particles  of  it  do  not  find  their  way  into  the  gold 
filings. 

There  are  certain  other  metals  which,  when  mixed  with  gold  in 
quantities  as  small  as  the  Y9V0  P^''^'  ^^  ^^^  mass,  render  it  quite  brittle 
and  unworkable.     These  are  bismuth,  lead,  antimony,  and  arsenic. 

Compounds  of  Gold. — Two  compounds  of  gold  with  oxygen  have 
been  obtained — AugO  and  Au.^O, — but  they  are  of  no  great  practical 
importance.  The  chlorides  of  gold  correspond  in  composition  to  the 
oxides. 

Auric  chloride — or  trichloride,  as  it  is  more  commonly  called — is 
prepared  by  dissolving  gold  in  nitro-hydrochloric  acid.  The  excess  of 
acid  is  driven  ofi"  by  evaporation  at  a  temperature  not  greater  than 
280°  F.  {=  138°  C.) ;  otherwise  a  part  of  it  at  least  will  be  converted 
into  aurous  chloride.     The  crystals  obtained  by  this  process  are  ruby-red 


GOLD.  109 

in  color  and  very  deliquescent.  The  composition  of  auric  chloride  is 
AuClg ;  atomic  weight,  303.1. 

Aurous  chloride  is  obtained  by  heating  the  crystallized  auric  chloride 
in  a  porcelain  evaporating-dish  to  about  347°  F.  (=  175°  C).  If  the 
temperature  is  carried  much  beyond  this  point,  say  to  392°  (=  200°  C), 
the  compound  will  be  decomposed  into  metallic  gold  and  chlorine  gas. 
Aurous  chloride  is  yellowish  in  color  and  nearly  insoluble  in  cold  water. 
Boiling  water,  however,  converts  it  into  auric  chloride  and  metallic  gold. 
Its  composition  is  AuCl ;  atomic  weight,  232.1. 

Auric  chloride  is  the  most  important  of  the  compounds  of  gold,  and 
is  the  source  from  which  most  of  the  preparations  of  gold  used  in  the 
arts  are  obtained.  There  are  iodides  of  gold  resembling  the  chloride  in 
many  respects.  Berzelius  also  described  an  aurous  sulphide.  These  are, 
however,  not  important. 

Purple  of  Cassius,  named  for  the  discoverer,  M.  Cassius,  is  employed 
by  manufacturers  of  porcelain  teeth  in  obtaining  the  gum  color,  and  in 
the  industrial  arts  for  imparting  a  red  color  to  glass  and  porcelain.  It 
is  a  compound  of  gold,  tin,  and  oxygen,  which  are  believed  to  be  grouped 
according  to  the  formula 

Au20.Sn02,SnO,Sn02  +  4.YL.f)} 

It  may  be  prepared  in  the  humid  way  by  adding  stannous  chloride 
(SnCL)  to  a  mixture  of  stannic  chloride  (SnCl^)  and  trichloride  of  gold. 
Seven  parts  of  gold  are  dissolved  in  aqua  regia  and  mixed  with  2  parts 
of  tin,  also  dissolved  in  aqua  regia.  This  solution  is  largely  diluted 
with  water,  and  a  weak  solution  of  1  part  of  tin  in  hydrochloric  acid  is 
added,  drop  by  drop,  until  a  fine  purple  color  is  produced.  The  purple  of 
Cassius  in  a  state  of  fine  division  remains  for  a  time  suspended  in  the 
water,  but  finally  subsides  as  a  purple  powder.  The  fresh  precipitate  dis- 
solves in  ammonia,  and  exposure  to  light  decomposes  the  purple  solution, 
during  which  process  its  hue  changes  to  blue,  and  it  finally  becomes 
colorless,  and  metallic  gold  is  precipitated,  the  binoxide  of  tin  being  left 
in  solution. 

Professor  Wildman  obtained  precisely  similar  results  by  a  dry  method 
in  which  an  alloy  of  gold,  silver,  and  tin  in  the  following  proportions  are 
melted  together  and  granulated : 

Pure  Silver 240    gr. 

Pure  Gold 24     " 

Pure  Tin 17^   " 

This  alloy  is  then  acted  upon  by  nitric  acid  until  the  silver  has  been 
entirely  dissolved,  when  the  solution  should  be  poured  off  and  the 
remaining  oxide  carefully  washed  until  all  traces  of  silver  are  removed. 
When  the  oxide  is  sufficiently  washed  the  purple  of  Cassius  should  be 
dried  by  gently  heating,  and  is  ready  to  be  incorporated  with  the  silicious 
material,  as  described  in  detail  in  the  chapter  on  Moulding  and  Carving 
Porcelain  Teeth. 

Hyposulphite  of  gold  and  soda,  the  sel  cVor  of  the  photographers,  is  a 
double  salt  formed  by  adding  a  solution  of  1  part  of  trichloride  of  gold 
to  a  solution  of  3  parts  of  hyposulphite  of  soda.     Alcohol,  in  which  the 

^  Bloxam's  Chemistry,  Organic  and  Inorganic. 


110  METALS  AND  ALLOYS. 

double  salt  is  soluble,  is  then  added.     The  formation  of  this  compound 
may  be  explained  by  the  equation — 

8(N02SP3)  +  2AUCI3  =  Au.,S,0„S(Nsi,8,0,)  +  6NaCl  +  2{lSa,Sp,). 

Fulminating  Gold. — When  ammonia  is  added  to  trichloride  of  gold, 
a  buif-colored  precipitate  results,  which  explodes  violently  when  gently 
heated.     Its  exact  composition  is  not  well  established. 

Discrimination  of  Gold. — Protochloride  of  tin  is  a  characteristic  test 
for  gold,  affording  a  purple-brown  precipitate.  The  smallest  portion  of 
gold  dissolved  in  a  large  quantity  of  water  may  be  detected  by  the  ad- 
dition of  a  few  drops  of  this  reagent.  Thus,  a  pale-brown  precipitate 
may  be  obtained  in  a  pint  of  water  containing  but  one-fiftieth  of  a  grain 
of  gold. 

Ferrous  sulphate  is  also  a  delicate  test  for  the  presence  of  gold,  and 
will  detect  the  merest  trace  of  it.  By  this  reagent  the  gold  is  thrown  down 
in  the  form  of  a  brown  powder,  which,  after  washing,  drying,  and  heating 
to  redness,  yields  the  metal  in  a  finely  divided  state. 

Sulphuretted  hydrogen  (HgS),  added  to  a  solution  of  trichloride  of  gold, 
affords  a  brown  precipitate  of  auric  sulphide.  Nitrate  of  mercury  also  pre- 
cipitates from  solution  a  brown  powder,  which  after  heating  yields  finely 
divided  gold.  Finely  divided  gold,  suspended  in  water,  imparts  a  violet 
or  red  color  to  it.  Colored  fluids  containing  minute  particles  of  gold  in 
a  state  of  suspension  may  be  obtained  by  the  action  of  phosphorus  dis- 
solved in  ether  upon  a  very  weak  solution  of  gold  in  aqua  regia.  After 
standing  for  a  long  time  the  fine  particles  of  gold  are  deposited,  having 
the  same  tint  as  that  which  they  previously  exhibited  when  suspended  in 
the  liquid.  The  blue  particles,  being  less  minute,  are  soonest  deposited, 
but  the  red  particles  require  many  months  to  settle  down.  The  one- 
hundredth  of  a  grain  of  gold  is  capable  of  imparting  a  deep  rose-color  to 
a  cubic  inch  of  fluid,  and  the  different  colors  thus  produced  are  taken 
advantage  of  in  painting  upon  porcelain,  a  beautiful  ruby-red  color  being 
the  result  of  the  pigment  thus  obtained. 

Assays  of  Gold  Ores,  Quartz,  etc. — The  specimens  of  ores  should 
first  be  heated  to  redness,  and  then  thrown  into  cold  water  to  facilitate 
powdering,  which  may  be  accomplished  in  an  ordinary  Wedgwood 
mortar.  Several  lots  of  300  grains  each  should  be  weighed  and  exam- 
ined separately,  and  the  assays  made  from  these  averaged  for  the  result. 
To  the  separate  portions  of  powdered  ore  equal  weights  of  litharge,  half 
their  weights  of  sodic  carbonate,  and  about  half  of  powdered  charcoal, 
are  added  and  thoroughly  mixed  with  the  ore.  Each  portion  is  then 
placed  in  a  crucible,  a  little  borax  sprinkled  over  the  top,  and  it  is  ready 
for  heating  in  a  suitable  blast-  or  wind-furnace.  The  heat  at  first  should 
be  gradual,  so  that  the  active  effervescence  caused  by  the  escape  of  car- 
bonic acid  from  the  soda  salt  may  not  force  portions  of  the  mixture  from 
the  crucible.  After  a  short  time,  however,  the  danger  from  this  cause 
having  passed,  the  heat  may  be  carried  to  bright  redness  or  until  the 
whole  has  fused.  An  ingot-mould  with  two  apertures  has  been  recom- 
mended for  the  reception  of  the  fused  mixture,  which  at  this  point  is 
ready  for  pouring,  the  slag  being  turned  into  one  concavity  and  the 
reduced  metal  into  the  other.     The  button  will  be  found  to  consist  of 


GOLD.  Ill 

lead  and  gold,  the  former  reduced  from  the  litharge  and  the  latter  from 
the  auriferous  ore.     These  are  to  be  separated  by  cupellation. 

If  the  ore  contains  much  iron  pyrites  or  is  of  the  nature  of  "  sweeps" 
(the  name  given  to  residues  which  accumulate  in  the  dental  laboratory 
and  other  places  where  gold  is  worked),  it  will  be  necessary  to  roast  it  in 
a  shallow  fire-clay  dish  placed  in  a  muffle,  and  in  the  case  of  pyrites  con- 
taining about  7  pennyweights  to  the  ton  the  operation  should  be  conducted 
with  1000  grains.  The  roasted  ore  is  then  fused  with  a  mixture  consist- 
ing  of  red  lead,  1000  grains;  sodic  carbonate,  600  grains;  powdered 
charcoal,  40  grains ;  and  borax,  500  grains.  The  mixture  is  introduced 
into  a  clay  crucible,  which  it  should  half  fill,  and  is  fused  in  an  air-fur- 
nace. The  button  of  reduced  lead  may  be  removed  either  by  pouring 
the  contents  of  the  crucible  into  a  mould  or  by  breaking  the  crucible 
when  cold. 

Assay  hy  Scorification. — Scorification  resembles  cupellation,  but  the 
oxide  of  lead  produced  in  the  operation,  instead  of  sinking  into  a  porous 
«up,  is  held  in  a  flat  saucer  of  fire-clay,  and  dissolves  the  earthy  constit- 
uents of  the  ore,  leaving  the  precious  metal  to  pass  into  another  portion 
of  lead,  which  remains  in  the  metallic  state.  About  200  grains  of  the 
roasted  ore  are  placed  in  the  scorifier,  and  intimately  mixed  with  500 
grains  of  granulated  lead  and  50  grains  of  borax.  The  contents  of  the 
scorifier  are  fused  in  a  muffle.  Air  is  admitted  to  oxidize  the  greater 
portion  of  the  lead.  At  the  conclusion  of  the  operation  the  litharge 
should  be  perfectly  fluid  and  cover  the  molten  lead.  The  slag  may  be 
freed  from  particles  of  precious  metal  by  the  addition,  at  the  conclusion 
of  the  operation,  of  a  small  quantity  of  powdered  anthracite,  which 
reduces  a  portion  of  the  litharge  to  metallic  globules,  which  fall  through 
the  slag  and  unite  with  the  lead  button.  The  gold  is  then  separated  by 
-cupellation,  and  the  silver,  with  which  it  is  almost  always  associated,  by 
parting  with  nitric  acid. 

Assaying. — This  term  refers  to  the  quantitative  estimation  of  one 
constituent  of  an  alloy  or  mineral,  and  is  accomplished  by  cupellation 
when  the  alloying  metal  is  copper,  and  "parting"  when  the  debasing 
metal  consists  of  silver.  Usually  both  operations  are  necessary.  From 
5  to  16  grains  of  the  gold  are  wrapped  in  sheet  lead,  with  pure  sil- 
ver equal  to  two  and  a  half  times  the  quantity  of  gold  supposed  to  be 
present.  The  weight  of  lead  employed  where  the  assay  is  standard 
gold^  is  8  to  1,  and  the  ratio  of  the  weight  of  lead  to  the  weight  of 
copper  assumed  to  be  present  is  100  to  1.  The  assay  is  now  to  be 
treated  by  cupellation,  a  process  which  is  thus  briefly  and  clearly  de- 
scribed by  Mr.  W.  Crookes  : 

"  The  gold  alloy  is  fused  with  a  quantity  of  lead  and  a  little  silver 
if  silver  is  already  present.  The  resulting  alloy,  which  is  called  the 
'  lead  button,'  is  then  submitted  to  fusion  on  a  very  porous  support  made 
of  bone-ash  and  called  a  '  cupel.'  The  fusion  is  effected  in  a  current  of 
air,  which  oxidizes  the  lead.  The  heat  is  sufficient  to  keep  the  oxide  of 
lead  fused.  The  porous  cupel  has  the  property  of  absorbing  melted 
oxide  of  lead  without  taking  up  any  of  the  metallic  globules,  exactly  in 
the  same  way  that  blotting-paper  will  absorb  water,  while  it  will  not 
liouch  a  globule  of  mercury.     The  heat  being  continued,  and  the  current 

'  22-carat,  or  coin. 


112  METALS  AND  ALLOYS. 

of  air  always  passing  over  the  surface  of  the  melted  lead  button,  and  the 
oxide  of  lead  or  litharge  being  sucked  up  by  the  cupel  as  fast  as  it  is 
formed,  the  metallic  globule  rapidly  diminishes  in  size  until  at  last  all 
the  lead  has  been  got  rid  of.  Now,  if  this  were  the  only  action  little 
good  would  have  been  gained,  for  we  should  have  put  lead  into  the  gold 
alloy  and  taken  it  out  again.  But  another  action  goes  on  while  the  lead 
is  oxidizing  in  the  current  of  air.  Other  metals,  except  the  silver  and 
gold,  also  oxidize,  and  are  carried  by  the  melted  litharge  into  the  cupel. 
If  the  lead  is,  therefore,  rightly  proportioned  to  the  standard  of  alloy, 
the  resulting  button  will  consist  of  only  gold  and  silver,  and  these  are 
separated  by  the  operation  of  parting,  which  consists  in  boiling  the  alloy 
(after  rolling  it  into  a  thin  plate)  in  strong  nitric  acid,  which  dissolves 
the  silver  and  leaves  the  gold  as  a  coherent  sponge."  ^ 

The  process  of  cupellation  is  generally  performed  'in  a  furnace  pro- 
vided with  a  muffle  for  the  reception  of  the  cupels,  and  arranged  so  a& 
to  admit  of  a  current  of  air  over  the  fused  button.  The  lead  used  in 
cupellation  should  be  of  absolute  purity ;  otherwise,  as  lead  is  always 
liable  to  contain  silver,  the  latter  would  necessarily  combine  with  the 
assay  and  vitiate  the  accuracy  of  the  result. 

Recovery  of  Gold  from  Sweepings  and  Other  Collections. — In 
addition  to  the  methods  of  treating  sweepings  and  the  residues  which 
accumulate  in  the  dental  laboratory  and  other  places  where  gold  is 
worked,  sweepings — which  consist  of  impurities  of  almost  every  kind, 
including  fragments  of  porcelain  teeth  and  other  infusible  substances — 
should,  as  a  preliminary  step,  be  carefully  gone  over  and  all  of  the  larger 
foreign  particles  removed  with  the  tweezers,  after  which  the  mass  should 
be  placed  in  a  large  crucible  and  brought  to  a  bright-red  heat,  without 
borax  or  other  fluxes,  for  the  purpose  of  incinerating  all  combustible 
materials  present.  On  cooling  it  will  be  found  that  the  bulk  of  the 
mass  has  greatly  decreased.  It  is  then  ready  for  washing  for  the 
purpose  of  getting  rid  of  ash  resulting  from  the  preliminary  heating. 
What  remains  should  be  placed  in  a  crucible  with  a  large  amount  of 
borax,  and  exposed  to  the  highest  heat  attainable  in  a  coal-stove  or 
furnace.  The  button  of  impure  gold  will  be  found  at  the  bottom  of  the 
crucible. 

Collections  from  the  trap  of  the  fountain  spittoon  will  be  found  to 
consist  of  fragments  of  gold,  amalgam,  oxyphosphate,  and  gutta-percha 
fillings,  with  pieces  of  porcelain  and  natural  teeth.  The  latter,  together 
with  the  larger  masses  of  amalgam,  should  be  removed  by  the  tweezers. 
The  mass  should  then  be  roasted  in  the  manner  described  in  the  treat- 
ment of  sweepings,  washed,  and  melted  with  a  very  large  amount  of 
borax,  the  success  of  the  operation  depending  very  much  upon  the 
amount  and  duration  of  heat  and  the  quantity  of  flux  used. 

Another  method,  which  has  been  highly  recommended,  consists  in 
fusing  the  sweepings  or  collection  from  the  spittoon  with  certain  sub- 
stances in  proportions  as  follows :  sweepings,  8  parts  ;  sodium  chloride, 
4  parts  ;  impure  potassium  carbonate,  4  parts ;  potassium  supertartrate, 
1  part ;  and  potassium  nitrate,  J  part.  These  are  to  be  mixed  thor- 
oughly and  melted  in  a  crucible,  and  in  order  to  secure  complete  separa- 
tion of  the  metals  from  extraneous  matter  the  crucible  with  its  contents 

'  See  "  Quartation." 


SILVER.  113 

should  remain  in  the  fire  at  the  highest  attainable  temperature  for  at 
least  an  hour.  The  resulting  button  of  impure  gold  will  necessarily  be 
of  uncertain  quality,  and  will  require  treatment  by  the  quartation  pro- 
cess to  reduce  it  to  pure  gold,  when  it  may  be  again  definitely  alloyed  to 
the  finest  required  for  use  in  the  dental  laboratory. 

Silver. 
Atomic  weight,  108.     Symbol,  Ag  (Argentum). 

Properties  of  Silver. — Silver  is  distinguished  from  all  other  metals 
by  its  brilliant  whiteness.  Its  specific  gravity  is  10.53.  In  hardness  it 
is  between  gold  and  copper.  It  is  one  of  the  most  ductile  and  malleable 
of  the  metals,  and  when  calculated  by  weight  it  is  not  even  surpassed  by 
gold.  For  example,  1  grain  of  gold  may  be  beaten  out  to  the  extent  of 
75  square  inches,  and  the  same  weight  of  silver  to  98  square  inches. 
Taking  a  cubic  inch  of  gold  at  4900  grains,  this  gold-leaf  is  3  g  g^g  ^  q  part 
of  an  inch  in  thickness,  or  about  twelve  hundred  times  thinner  than 
ordinary  printing-paper.'  But  the  silver,  though  spread  over  a  larger 
surface,  will  be  thicker,  owing  to  the  ditlerence  of  specific  gravity 
between  gold  and  silver.  The  extent  of  the  malleability  of  gold  and 
silver  has  not  yet  been  definitely  determined,  as  the  means  employed  to 
test  it  have  failed  before  there  was  any  appearance  of  the  malleability  of 
either  of  them  being  exhausted.^ 

In  tenacity  silver  surpasses  gold.  It  fuses  at  about  1873°  F.,  and 
during  the  fusion  absorbs  oxygen  to  the  extent  of  about  twenty-two 
times  its  own  volume ;  but  at  the  instant  of  solidification  it  undergoes 
considerable  expansion,  while  at  the  same  time  it  parts  with  the  oxygen,, 
which  makes  its  escape  through  the  thin  crust  formed  over  the  fluid: 
metal,  carrying  with  it  fine  globules  of  the  metal,  which  may  be  observed 
adhering  to  the  sides  of  the  crucible.  It  is  the  best  conductor  of  heat 
and  electricity  known.  It  possesses  no  direct  attraction  for  oxygen ; 
hence  it  is  not  oxidized  by  dry  or  moist  air  at  any  temperature.  It  is, 
however,  oxidized  by  ozone,  and  tarnished  by  air  containing  sulphuretted 
hydrogen,  which  blackens  the  surface  with  a  superficial  layer  of  sulphide 
of  silver,  which  may  be  removed  by  a  solution  of  cyanide  of  potassium. 

With  the  exception  of  nitric,  silver  is  not  affected  by  dilute  acids  ; 
but  hot  concentrated  sulphuric  acid  converts  it  into  sulphate  of  silver, 
and  when  boiled  with  strong  hydrochloric  acid  it  dissolves  to  a  slight 
extent  in  the  form  of  chloride  of  silver,  which  is  precipitated  by  the 
addition  of  water. 

Occurrence  and  Distribution. — In  the  Middle  Ages,  Austria  was  the 
chief  source  from  which  silver  was  obtained  as  an  associate  metal  with 
lead.  At  the  present  day  the  United  States,  Peru,  and  Mexico  supply 
large  quantities. 

Silver  is  found,  first,  as  native  silver,  occurring  in  flat  masses  occa- 
sionally and  sometimes  crystalline  in  form.  In  this  country  it  occurs 
with  native  copper,  masses  frequently  being  met  with  in  which  the  two 
metals  are  diffused,  the  silver  showing  in  specks  upon  the  copper. 

'  Gold  has,  for  the  sake  of  experiment,  been  beaten  out  to  the  extent  given  above,  but 
the  3-75-oVt)  cf  of  an  inch,  as  given  on  page  94,  is  as  thin  as  is  ever  required  for  practical 
purposes.  2  y^  Chandler  Roberts,  assayer  Eoyal  Mint. 

8 


114  METALS  AND  ALLOYS. 

Native  silver  is  usually  free  from  any  considerable  admixture  with 
other  metals,  although  it  invariably  contains  traces  of  gold,  antimony, 
etc.     It  is  also  found  as  chloride,  iodide,  and  bromide. 

The  most  common  ores  from  which  silver  is  derived  are  those  result- 
ing from  combination  with  sulphur  and  sulphides.  These  may  be  divided 
into  three  kinds.  First  may  be  mentioned  the  common  sulphide  of 
Mexico,  called  "  vitreous  sulphide."  It  is  a  protosulphide,  is  very  fusi- 
ble, and  readily  yields  silver  when  made  to  give  up  its  sulphur.  Another 
sulphide,  closely  resembling  the  first,  called  '^  brittle  silver  ore,"  is  found 
in  South  America  and  in  some  parts  of  Europe.  It  is  readily  decom- 
posed by  heat,  and  during  exposure  to  high  temperatures  evolves  fumes 
of  arsenic  and  antimony.  A  third  sulphide,  found  in  nearly  all  silver- 
mines  in  the  form  of  ruby-colored,  transparent  crystals,  is  called  "  red 
silver  ore,"  and  is  associated,  to  some  extent,  with  oxides.  The  com- 
position of  this  ore  has  been  given  as  follows  :  Silver,  56  to  62  ;  anti- 
mony,  16   to  23;  sulphur,   11   tq  14;  oxygen,  8  to  10. 

The  chloride,  or  native  horn-silver,  is  quite  an  abundant  ore  of  South 
America  (Chili).  It  is  a  true  chloride,  and,  like  precipitated  chloride  of 
silver,  darkens  when  exposed  to  sunlight.  Its  composition  is  given  as — 
silver,  75.3  ;  chlorine,  24.7. 

Methods  of  Separating  Silver  from  its  Ores. — As  much  of  the  silver 
of  commerce  is  extracted  from  ores  too  poor  to  admit  of  its  economical 
separation  by  any  process  of  melting  or  fusing,  even  in  regions  where 
fuel  is  plenty,  recourse  to  the  method  known  as  "  amalgamation "  is 
necessary.  This  depends  simply  upon  the  easy  solubility  of  silver  and 
associated  metals  in  mercury.  The  ore  is  crushed  to  powder,  mixed 
with  a  sufficient  quantity  of  common  salt,  and  roasted  at  a  dull-red  heat 
in  a  suitable  furnace.  By  this  treatment  any  sulphide  of  silver  con- 
tained is  converted  into  chloride.  The  mixture,  which  consists  of  much 
earthy  matter,  metallic  oxides,  soluble  salts,  silver  chloride,  and  metallic 
silver,  is  sifted  and  placed  in  barrels  arranged  to  revolve  on  axes.  Scraps 
of  iron  and  water  are  added,  and  the  whole  agitated  together  for  the 
purpose  of  reducing  the  silver  chloride  to  the  metallic  state.  A  sufficient 
quantity  of  mercury  is  then  added,  and  the  agitation  continued  until  the 
metallic  particles  are  dissolved,  forming  a  fluid  amalgam  which  is  readily 
separated  from  the  mud  or  earthy  matter  by  subsidence  and  washing.  It 
is  then  strained  through  a  strong  linen  cloth  or  other  suitable  fabric  to 
separate  the  fluid  mercury  from  the  more  solid  portions  of  amalgam. 
These  latter  are  subsequently  exposed  to  heat  in  a  retort,  by  which  the 
remaining  mercury  is  distilled  off.  The  silver,  more  or  less  impure  from 
admixture  with  other  metals  contained  in  the  ore,  is  thus  obtained. 

In  order  to  prevent  loss  during  the  amalgamation  process  in  conse- 
quence of  a  tendency  on  the  part  of  the  mercury  to  combine  with  sul- 
phur, oxygen,  etc.,  technically  known  as  "  flouring,"  in  which  condition 
it  may  be  washed  away  together  with  the  silver  it  has  taken  up,  from  1 
to  2  per  cent,  of  sodium  is  added  to  the  mercury.  The  great  affinity  of 
sodium  for  sulphur  and  oxygen  prevents  "  flouring  "  of  the  mercury. 

Considerable  quantities  of  silver  are  obtained  from  argentiferous 
galena,^  and,  indeed,  it  may  be  stated  that  nearly  every  specimen   of 

'  Silver  is  invariably  present  in  this  form  of  lead  ore,  but  not  always  in  paying 
quantities. 


SILVER.  115 

native  lead  sulphide  will  be  found  to  contain  traces  of  the  nobler  metal. 
When  the  proportion  of  the  precious  metal  present  is  sufficiently  large 
to  ensure  its  profitable  separation,  the  ore  is  reduced  as  usual/  the  silver 
remaining  with  the  lead,  and  is  then  treated  according  to  a  process  dis- 
covered by  Mr.  Pattinson,  by  whom  it  was  found  that  when  lead  con- 
taining a  considerable  amount  of  silver  is  fused  and  carefully  stirred 
while  it  is  allowed  to  cool  slowly,  crystals  much  less  rich  in  silver  than 
the  mass  before  melting  will  form,  and  separate  and  subside  to  the  bot- 
tom. These  crystals  of  poorer  lead  are  removed  by  means  of  perforated 
ladles.  The  silver  is  thus  concentrated.  The  method  of  separating 
silver  from  lead,  as  practised  on  a  large  scale,  is  thus  described  by  Mr. 
Makins  in  his  Ifanual  of  31etallurgy : 

"  A  series  of  iron  pots,  from  nine  to  twelve  in  number,  are  employed. 
These  are  hemispherical,  about  5  feet  in  diameter,  and  calculated  to 
hold  a  charge  of  about  nine  tons  of  metal  each.  They  are  set  in  brick 
furnaces  adjacent  to  one  another,  but  with  quite  distinct  flues,  furnaces, 
dampers,  etc.  The  lead,  assorted  according  to  its  richness  in  silver,  is 
then  placed  in  the  pots  in  the  following  order  :  Some  lead  containing  10 
ounces  of  silver  per  ton  having  to  be  worked,  9  tons  of  it  would  be 
placed  in  the  fifth  pot  and  melted.  After  complete  fusion  it  is  skimmed 
with  a  perforated  ladle,  which  removes  the  dry  oxides  for  subsequent  re- 
duction, while  it  permits  the  fluid  lead  to  run  back  into  the  pot.  The  fire 
is  then  drawn,  and  the  metal  stirred  while  it  slowly  cools  until  it  begins 
to  thicken.  The  workman  at  this  stage  of  the  operation  employs  an 
irou  ladle  of  18  inches  in  diameter  by  5  inches  deep,  perforated  with 
half-inch  holes  and  furnished  with  a  very  long  handle.  This  handle 
he  raises  above  his  head,  sinking  the  bowl  into  the  lead  until  it  reaches 
the  bottom.  Then,  by  using  the  handle  as  a  lever  and  depressing  it  as 
far  as  possible,  the  ladle  full  of  crystals  is  brought  into  view,  and  by 
means  of  a  hook  and  chain  fastened  to  a  crane  is  suspended  and  left  to 
thoroughly  drain,  after  which  the  crystals  are  turned  into  the  fourth  pot. 
This  operation  is  continued  until  two-thirds  of  the  lead  in  the  fifth  pot 
have  been  passed  over  in  crystals  to  the  fourth  pot,  under  which  a  fire  is 
made  and  the  crystals  again  melted.  The  remaining  3  tons  of  molten 
lead  in  the  fifth  pot,  which  by  the  separation  of  the  crystals  contains  sil- 
ver equalling  20  ounces  per  ton,  is  now  ladled  into  the  sixth  pot.  The 
results  of  the  preceding  operations  may  be  summed  up  as  follows  :  In 
pot  5,  9  tons  of  ten-ounce  lead  equals  90  ounces  of  silver,  of  which  6  tons 
of  five-ounce  (30  ounces  silver)  works  into  pot  4,  and  3  tons  of  twenty- 
ounce  (60  ounces  silver)  is  ladled  into  pot  6.  The  work  now  proceeds 
until  all  the  pots  are  in  operation.  Three  tons  of  five-ounce  lead  would 
be  added  to  the  6  tons  passed  into  pot  4,  while  6  tons  of  twenty-ounce 
lead  would  be  carried  into  pot  6.  Six  tons  from  pot  6  Avould  work  into 
No.  5,  and  3  tons  in  bottoms  will  be  put  back  into  the  same  pot  from 
No.  4,  filling  it  again  without  the  addition  of  pig-lead.  The  bottoms  or 
portions  which  remain  after  the  ladling  become  by  tliat  process  so  rich 
in  silver  as  to  often  contain  600  ounces  to  the  ton.  This  is  finally  sub- 
mitted to  cupellation,  by  which  means  the  complete  separation  of  the 
silver  is  efl^ected." 
-    The  cupel  and  its  application  may  be  thus  briefly  described  :  Bone- 

^  See  cliapter  on  "  Lead." 


116  METALS  AND  ALLOYS. 

ash  is  mixed  with  water,  made  into  a  cup  in  a  suitable  mould,  and  dried. 
This  is  called  the  cupel,^  and  has  the  property  of  absorbing  oxides  when 
they  are  combined  with  oxides  of  lead  in  a  state  of  fusion.  Impure  sil- 
ver is  mixed  with  a  certain  quantity  of  lead,  determined  by  the  amount 
of  impurity  supposed  to  exist  in  the  alloy.  The  mixture  is  melted  in 
the  cupel  in  a  current  of  air  until  the  whole  of  the  lead  is  converted  into 
oxides,  which  in  a  fused  state  sinks  into  the  porous  cupel,  carrying  along 
with  it  the  impurities,  the  silver  being  left  behind  in  a  pure  state.  The 
whole  operation  is  based  on  the  absence  of  attraction  for  oxygen  evinced 
by  the  noble  metals  even  when  exposed  to  high  temperatures,  and  on  the 
affinity  possessed  by  the  base  metals  for  oxygen  under  similar  condi- 
tions. 

Cupellation  may  be  accomplished  either  in  a  muffle  arranged  with 
reference  to  the  passage  of  a  current  of  air,  so  that  oxygen  may  be  freely 
supplied  to  the  melted  metal,  or  it  may  be  performed  under  the  oxidizing 

flame  of  the  blowpipe.  The  latter  ope- 
Ficx.  104.  ration  is  often  employed  in  blowpipe  analy- 

--  — ---^^  sis.     A  certain  amount  of  the  alloy  is  mixed 

/^'^^^^^||||p||ir^t5>CX  with  about  four  times  its  weight  of  pure  lead, 
L  ^^W^  ^J^yf        ^^^  *^®^  placed  on   the  cupel  and  the  oxi- 

l|||fe---._f_ --TiijiBf         dizing  flame  of  the  blowpipe  directed  on  it. 

||1||| .    --^c-i;  ^  iilfijiJB  The  oxidizing  process  soon  begins,  and  in 

lllffe:  ■  '-^UirnKK  ^^o^*  thirty  minutes  all  the  lead  will  be 

llllllir  ■''iSSl,\i\i^^^B  _       converted  into  litharge,  which  is  fusible  and 

l|#'i  •     ^'''  I'lllii^^  is  readily  absorbed  into  the  porous  substance 

^^~------^_.:jWii^^  of  the  cupel,  carrying  with  it  all  the  oxidiz- 

The  cupel.  able  metals  that  may  be  present.     At  this 

point  the  button,  having  parted  with  every 
trace  of  the  latter,  assumes  an  exceedingly  bright  appearance,  technically 
called  the  "brightening  of  the  button,"  thus  offering  a  certain  means 
of  ascertaining  when  the  process  of  cupellation  is  complete.  Cupellation 
under  the  oxidizing  flame  of  the  blowpipe  for  quantitative  discrimina- 
tion requires  careful  management,  particularly  when  the  silver  has  parted 
with  the  base  metals  and  approaches  a  state  of  purity  ;  for  it  is  at  this 
stage  of  the  operation  that  the  well-known  property  of  melted  silver,  of 
absorbing  oxygen  from  the  atmosphere  and  then  parting  with  it  as  it 
approaches  the  point  of  solidification,  may  be  observed.  The  giving  off 
of  the  absorbed  oxygen  is  what  causes  "  sputtering,"  by  which  minute 
globules  of  the  metal  are  thrown  off  and  lost,  thus  rendering  the  assay 
inaccurate. 

Besides  the  method  of  obtaining  silver  above  described,  the  metal 
may  be  obtained  by  converting  sulphide  into  chloride,  the  latter  being 
easily  reduced  to  metallic  silver  by  the  wet  method.  The  sulphide  is 
also  sometimes  converted  into  sulphate,  when  the  silver  may  be  reduced 
from  the  solution  by  precipitation. 

Another  method  of  separating  silver  from  its  ores  consists  in  roasting 
the  latter  with  common  salt  to  convert  the  silver  into  chloride,  which 
is  dissolved  out  of  the  mass  by  means  of  a  strong  solution  of  chloride  of 
sodium ;  the  silver  is  then  recovered  in  the  metallic  state  by  precipitating 
with  copper.     Hyposulphite  of  soda  has  also  been  employed  to  dissolve 

^  Cupels  may  be  obtained  at  the  chemists'  furnishing-shops  ready  for  use. 


SILVER.  117 

out  the  chloride  of  silver,  the  resulting  solution,  being  precipitated  by 
sulphide  of  sodium,  yielding  sulphide  of  silver,  which  requires  roasting 
to  drive  off  the  sulphur  and  liberate  the  metallic  silver. 

Compounds  of  Silver. — There  are  three  compounds  of  silver  with 
oxygen  :  the  suboxide,  AgO ;  the  oxide,  AgP  ;  and  the  peroxide,  which 
is  thought  to  have  the  formula  of  Ag.p.^-  The  oxide  is  the  only  one 
having  any  practical  importance.  Being  the  base  contained  in  the  salts 
of  silver,  it  is  obtained  by  adding  caustic  potassa  or  baryta-water  to  a 
solution  of  nitrate  of  silver. 

Silver  nitrate  (AgNOg)  is  prepared  by  dissolving  silver  in  nitric  acid 
by  the  aid  of  gentle  heat,  after  which  it  is  evaporated  to  dryness  or  until 
it  crystallizes.  These  crystals  are  colorless,  transparent,  and  soluble  in 
an  equal  weight  of  cold  and  in  half  the  quantity  of  boiling  water.  They 
are  also  soluble  in  alcohol.  Nitrate  of  silver  is  fusible,  and  when  poured 
into  cylindrical  moulds  forms  the  lunar  caustic  employed  by  surgeons. 
At  high  temperatures  (red  heat)  it  is  decomposed,  yielding  pure  metallic 
silver. 

Silver  sulphate  (AgaSO^)  is  prepared  by  boiling  metallic  silver  in 
sulphuric  acid. 

Silver  sulphide  is  remarkable  for  being  so  soft  and  malleable  that 
medals  may  be  struck  from  it.  It  may  be  formed  as  a  black  precipitate 
by  the  action  of  hydrogen  sulphide  (H2S)  upon  a  solution  of  silver 
nitrate,  or  it  may  be  formed  by  heating  silver  with  sulphur  in  a  covered 
crucible.  It  is  the  affinity  existing  between  these  two  elements  which 
renders  the  combination  of  silver  and  vulcanizable  rubbers  impractica- 
ble. Silver  sulphide  is  not  soluble  in  dilute  sulphuric  or  hydrochloric 
acid,  but  is  readily  dissolved  by  nitric  acid.  Metallic  silver  also  dis- 
solves sulphide  of  silver  when  melted  with  it. 

Silver  chloride  (AgCl)  is  the  form  into  which  silver  is  commonly 
converted  in  separating  it  from  other  metals  or  from  its  ores.  It  is  a 
white,  curdy  precipitate,  and  may  be  obtained  from  a  solution  of  the 
nitrate  by  the  addition  of  sodium  chloride  or  hydrochloric  acid.  When 
freshly  prepared  it  is  perfectly  white,  but  soon  darkens,  and  eventually 
becomes  quite  black  by  exposure  to  solar  light,  parting  with  a  portion 
of  its  chlorine  and  becoming  a  subchloride  (AggCl). 

Silver  chloride  may  also  be  formed  by  suspending  a  silver  leaf  in  a 
glass  vessel  containing  chlorine  gas,  and  when  thus  prepared  it  is  not 
blackened  by  exposure  to  light.  Argentic  chloride  is  fusible  at  500°  F. 
A  much  higher  heat  converts  it  into  vapor,  but  does  not  decompose  it. 
It  is  soluble  in  ammonia. 

Discrimination. — The  chlorides  and  hydrochloric  acid  precipitate 
white  argentic  chloride,  and  so  delicate  is  the  test  that  when  1  part  of 
silver  is  dissolved  in  200,000  times  its  weight  of  water  it  may  be  readily 
detected  by  the  opalescence  which  is  imparted  to  the  fluid  by  the  pre- 
cipitant. This  precipitate  is  always  changed  to  a  violet-black  by  expos- 
ure to  light,  but  the  presence  of  mercury  ^  will  prevent  discoloration.  It 
is  insoluble  in  nitric  acid,  but  is  readily  soluble  in  ammonia,  and  may  be 
fused  to  a  horny  mass  without  decomposition. 

Sulphuretted  hydrogen  added  to  a  solution  containing  silver  throws 
down  a  black  precipitate  of  silver  sulphide,  which  is  not  soluble  in  dilute 

^  Mercurous  chloride. 


118  METALS  AND  ALLOYS. 

acids,  alkalies,  or  potassic  cyanide.     Sulphuric  acid  at  a  temperature  of 
212°  F.  will,  however,  dissolve  it,  with  separation  of  the  sulphur. 

Ammonia  or  potassa,  when  employed  as  a  precipitant,  throws  down  a 
brown  oxide,  insoluble  in  the  latter,  but  soluble  in  the  former,  and  if 
freely  exposed  to  air  this  solution  will  deposit  fulminating  silver. 

The  blowpipe  is  frequently  used  in  the  discrimination  of  silver  com- 
pounds, which  when  heated  on  charcoal  with  sodic  carbonate  yield  a 
bright  bead  of  metallic  silver,  often  accompanied  by  a  red-colored 
deposit  on  the  charcoal. 

Quantitatively,  the  estimation  of  silver  may  be  accomplished  either 
by  the  usual  humid  process  or  by  assaying.  The  first  consists  in  pre- 
cipitating the  metal  as  chloride,  which  is  to  be  separated  and  weighed. 
The  precipitation  is  effected  as  follows  :  The  silver  solution  is  acidulated 
by  nitric  acid ;  hydrochloric  acid  or  sodic  chloride,  slightly  in  excess,  is 
then  added,  but,  as  silver  chloride  is  to  a  certain  extent  soluble  in  either 
of  these,  an  undue  excess  must  be  avoided.  The  chloride  must  now  be 
carefully  and  repeatedly  washed  and  filtered  in  a  thoroughly  dry  filter, 
previously  weighed.  After  the  solution  has  passed  through  the  filter 
the  latter  with  its  contents  is  dried  and  weighed,  and  the  weight,  minus 
the  weight  of  the  filter,  will  be  the  quantity  of  silver  chloride  present. 

The  dry  method  or  assaying  process  consists  in  forming  an  alloy  of 
the  silver  with  lead,  and  is  especially  applicable  to  ores  and  the  sweepings 
of  the  dentist's  laboratory.  The  specimen  to  be  treated  is  heated  with 
from  twelve  to  thirty  times  its  weight  of  pure  granulated  lead  in  a  bone- 
ash  cupel,  which  is  placed  in  a  muffle  so  arranged  that  a  current  of 
atmospheric  air  may  pass  freely  over  the  vessel  and  oxidize  the  lead. 
This  oxide  of  lead,  being  quite  fusible,  combines  with  any  base  metal 
present  and  oxidizes  it,  uniting  subsequently  with  the  oxide  as  a  fusible 
slag,  while  the  gold  or  silver  will  be  held  by  the  unoxidized  portion  of 
the  lead.  In  the  treatment  of  specimens  of  alloys,  such  as  plate  or  coin, 
a  quantity  of  the  specimen  is  accurately  weighed  and  mixed  with  from 
four  to  five  times  its  weight  of  pure  granulated  lead.  It  is  then  placed 
in  the  cupel  and  exposed  to  heat,  as  above  described,  until  all  the  lead  is 
oxidized  or  converted  into  litharge,  when  the  remaining  button  assumes 
the  brilliant  appearance  of  surface  before  alluded  to,  which  denotes  that 
the  base  metals  or  oxidizable  constituents  have  been  oxidized  and  taken 
up  by  the  lead  oxide.  This  button  is  then  to  be  weighed  by  means  of  a 
delicate  assay-balance,  and  the  loss  of  weight  shows  the  proportion  of 
alloy  that  wa's  present. 

Pure  Silver. — Pure  silver,  which  is  reckoned  as  1000  fine,  may  be 
obtained  from  standard  or  other  grades  of  silver  by  dissolving  them  in 
nitric  acid  slightly  diluted  with  water,  the  solution  being  much  facilitated 
by  exposure  to  gentle  heat.  If  gold  be  associated  with  the  alloy,  it  will 
be  found  at  the  bottom  of  the  vessel,  in  which  case  it  will  be  necessary 
to  use  a  siphon  to  remove  the  argentic  nitrate  solution.  The  silver  is 
now  to  be  precipitated  in  the  form  of  chloride  by  the  addition  of  an  excess 
of  common  salt.  When  all  has  subsided  the  liquid  is  carefully  poured 
off  and  the  chloride  thoroughly  washed  to  remove  all  traces  of  acid.  The 
chloride  is  then  placed  in  water  acidulated  with  hydrochloric  acid  (an 
ounce  of  chloride  requiring  6  to  8  ounces  of  water),  and  pieces  of  clean 
wrought  iron  put  in  it,  when  a  copious  evolution  of  hydrogen  follows. 


SILVER.  119 

which,  uniting  with  the  chlorine  of  the  argentic  chloride,  liberates  metallic 
silver.  The  latter  should  not  be  disturbed  until  the  last  particle  of  it  is 
thus  reduced,  when  it  will  be  found  to  be  a  spongy  mass.  The  undis- 
solved iron  should  now  be  carefully  removed,  the  ferrous  and  ferric 
chloride  carefully  decanted,  and  the  silver  washed  in  hot  water  contain- 
ing about  one-tenth  its  bulk  of  hydrochloric  acid.  This  is  repeated 
several  times,  and  finally  the  silver  is  again  thoroughly  washed  with  pure 
hot  water.  The  silver,  after  drying,  is  then  ready  for  melting,  and  if 
care  has  been  observed  in  the  process  it  will  be  found  to  be  of  a  fineness 
of  999.7  parts  in  1000,  the  0.3  of  impurity  present  being  due  to  traces 
of  iron.  The  chlorides  may  be  acidulated  with  sulphuric  acid,  and 
reduced  with  zinc  instead  of  iron. 

Another  method  of  precipitating  silver  in  the  metallic  form  consists 
in  placing  a  sheet  of  copper  in  a  solution  of  argentic  nitrate.  The  metal 
is  thrown  down  in  a  crystalline  form.  Silver  thus  obtained  is  never  free 
from  traces  of  copper. 

Pure  silver  can  only  be  obtained  from  samples  of  a  lower  grade  by 
fusing  the  pure  chloride  with  sodic  carbonate.  The  reaction  is  shown 
in  the  equation  : 

2AgCl  +  Na^COg  =:  Ag^  +  2NaCl  +  O  +  CO.. 

Owing  to  the  copious  evolution  of  carbonic-acid  gas  which  takes  place 
during  the  decomposition,  some  of  the  silver  may  be  thrown  from  the 
crucible,  and  loss  may  occur  by  the  absorption  by  the  crucible  of  some 
of  the  fused  chloride.  To  avoid  this  the  sides  of  the  vessel  should  be 
coated  with  a  hot  saturated  solution  of  borax.  A  composition  of  100 
parts  of  argentic  chloride,  70.4  of  calcic  carbonate  (chalk),  and  4.2  of 
charcoal  has  been  recommended  as  a  means  of  obtaining  pure  silver. 
This  mixture  is  heated  to  dull  redness  for  thirty  minutes,  and  is  then 
raised  to  full  redness  ;  carbonic  acid  and  carbonic  oxide  are  given 
ofP;  the  calcic  chloride  is  converted  into  calcic  oxychloride,  underneath 
which,  in  the  bottom  of  the  crucible,  will  be  found  the  button  of  pure 
silver. 

Alloys  of  Silver. — In  consequence  of  its  softness,  silver  in  the  pure 
state  is  liable  to  considerable  loss  by  attrition.  For  all  useful  purposes, 
however,  the  requisite  amount  of  hardness  may  be  conferred  upon  it  by 
the  addition  of  a  small  proportion  of  copper.  Thus,  silver  for  coinage 
and  manufacturing  purposes  usually  contains  in  1000  parts  from  900  to 
925  of  silver  and  from  75  to  100  of  copper.  The  term  "standard  silver" 
refers  to  the  metal  thus  alloyed  with  copper,  that  of  the  United  States 
coinage  being — silver  900  parts,  copper  100.   . 

Previous  to  the  introduction  of  vulcanized  rubber  as  a  base  for  arti- 
ficial dentures  standard  silver  was  much  employed  in  the  United  States 
for  temporary  dentures  when  cheapness  was  an  important  consideration. 
In  England  a  much  more  durable  alloy  is  used,  in  which  the  alloying 
metal  is  platinum,  in  the  proportion  of  from  3  to  10  grains  of  the  latter 
to  each  pennyweight  of  silver.  The  advantages  possessed  by  this  alloy 
over  ordinary  standard  silver  may  be  summed  up  as  follows  :  It  resists 
wear  better,  and  not  even  a  suspicion  can  be  reasonably  entertained  of 
any  ill  effects  occurring,  either  locally  or  to  the  general  system,  from  its 
presence  in  the  mouth.     It  permits  of  the  employment  of  a  higher  grade 


120  METALS  AND  ALLOYS. 

of  solder,  and  it  is  a  much  more  rigid  alloy  than  ordinary  standard  or 
coin  silver.  Hence  it  makes  a  stronger  artificial  denture,  which  is  less 
likely  to  have  its  adaptation  impaired  by  bending.  But,  while  silver  is 
improved  in  some  respects  when  platinum  is  the  sole  alloying  component, 
it  must  not  be  supposed  that  its  affinity  for  sulphur  is  thus  materially 
lessened,  or  that  its  tendency  to  blacken  when  brought  into  contact  with 
that  element  or  its  compounds  is  obviated.  Indeed,  it  may  be  stated 
that  platinum  added  to  silver  in  such  small  quantities  does  not  wholly 
protect  the  latter  from  the  action  of  its  ordinary  solvents.  Such  an  alloy 
of  silver,  for  instance,  would  not  only  be  readily  dissolved  by  nitric  acid, 
but  the  platinum  also,  though  unaffected  ordinarily  by  that  menstruum, 
would  readily  yield  to  it  when  combined  with  silver. 

This  alloy  of  silver,  which  is  known  in  England  as  "  dental  alloy," 
often  contains  from  25  to  30  per  cent,  of  platinum.  To  separate  the 
latter  metal  from  the  silver  the  alloy  is  dissolved  in  nitric  acid,  which  on 
the  addition  of  heat  will  dissolve  all  of  the  silver  with  about  10  per 
cent,  of  the  platinum.  On  introducing  a  bar  of  copper  into  this  solution 
the  silver  and  platinum  are  quickly  precipitated  in  a  metallic  state.  This 
precipitate  is  again  placed  in  nitric  acid,  which  redissolves  the  silver, 
leaving  the  platinum  untouched,  which,  however,  may  be  dissolved,  with 
the  other  15  or  20  per  cent,  of  the  platinum  left  at  first,  in  aqua  regia. 
Precipitating  by  an  excess  of  ammonium  chloride,  evaporating  to  dryness, 
and  igniting  yields  pure  platinum.  The  silver  may  be  recovered  in  the 
usual  way  by  precipitation  in  the  form  of  a  chloride,  which  may  be  easily 
reduced  to  a  metallic  state  by  treating  with  a  plate  of  zinc  in  acidulated 
water. 

It  is  a  somewhat  common  belief  that  the  putting  together  of  silver 
and  platinum  in  the  formation  of  an  alloy  of  this  kind,  owing  to  the 
infusibility  of  platinum  and  the  wide  diiference  in  the  fusing-points  of 
the  two,  is  a  matter  of  great  difficulty.  It  should  be  borne  in  mind, 
however,  that  between  the  metals  more  or  less  affinity  exists,  especially 
at  high  temperatures  ;  hence  it  is  only  necessary  to  introduce  the  plati- 
num, rolled  into  thin  ribbons,  into  the  crucible  containing  the  silver  in  a 
state  of  complete  fusion,  and  the  platinum  will  be  observed  to  quickly 
fuse  and  mix  with  the  other  metal.  It  is  sometimes  thought  advisable 
to  add  larger  proportions  of  platinum  than  the  quantity  here  given.  This 
may  be  done  by  adding  the  platinum  until  the  alloy  becomes  infusible ; 
and  this  result  will  be  attained  as  soon  as  sufficient  platinum  is  added  to 
raise  the  fusing-point  of  the  alloy  above  the  capacity  of  the  ordinary 
melting  apparatus. 

Von  Echart's  alloy,  employed  to  some  extent  in  France  as  a  base  for 
artificial  dentures,  is  composed  of  the  following  proportions  :  silver, 
3.53;  platinum,  2.40;  and  copper,  11.71.  It  is  very  elastic  (which 
property  it  does  not  lose  by  annealing)  and  can  be  highly  polished. 

Silver  Solders. — When  the  plate  to  be  united  consists  of  pure  silver 
alloyed  with  platinum,  the  solder  may  be  formed  of  the  standard  metal 
(coin),  with  the  addition  of  from  one-tenth  to  one-sixth  its  weight  of 
zinc  according  to  the  proportion  of  platinum  contained  in  the  alloy. 
Silver  solders  are,  however,  generally  composed  of  silver,  copper,  and 
zinc,  or  silver  and  brass,  in  variable  proportions,  of  which  the  following 
are  examples  i 


PLATINUM.  121 

No.  1} 

Silver 66  parts. 

Copper    30      " 

Zinc 10      " 

No.  ^? 

Silver 6  dwt. 

Copper    2    " 

Brass 1    " 

No.  3. 

Silver 5^  dwt. 

Brass  wire 40  gr. 

In  putting  together  the  constituents  of  silver  solders  the  affinity  for 
oxygen  manifested  by  zinc,  brass,  and  copper  when  exposed  to  high 
temperatures  should  be  remembered,  and  in  order  to  guard  against  loss 
the  mode  of  procedure  should  be  as  follows  :  The  silver,  placed  in  a 
clean  crucible,  with  a  sufficient  quantity  of  borax  to  cover  it,  should  be 
thoroughly  fused,  and,  without  permitting  it  to  cool  in  the  least,  the 
zinc,  brass,  or  copper,  as  the  case  may  be,  should  be  quickly  added. 
Before  pouring  it  should  be  shaken  or  agitated  to  ensure  admixture. 
When  cool  it  may  be  removed  from  the  ingot-mould  and  rolled  into 
plate  of,  say,  No.  27  of  the  standard  gauge. 

The  surface  of  standard  silver  may  be  whitened  by  being  heated  and 
immersed  in  dilute  sulphuric  acid.  It  is  in  this  way  that  frosted  silver 
is  produced.  The  acid,  dissolving  the  oxide  of  silver  from  the  surface, 
leaves  a  quite  pure  superficial  film. 

Silver  may  be  deposited  upon  the  surface  of  another  metal  by  con- 
necting the  article  to  be  silvered  with  the  negative  (zinc)  pole  of  the 
galvanic  battery,  and  then  immersing  it  in  a  solution  made  by  dissolving 
cyanide  of  silver  in  a  solution  of  cyanide  of  potassium.  The  current 
decomposes  the  argentic  cyanide,  and  the  metal  is  deposited  upon  the 
object  connected  with  the  negative  pole.  During  this  decomposition  the 
cyanogen  liberated  at  the  positive  (copper  or  platinum)  pole  acts  upon  a 
silver  plate  with  which  this  pole  is  connected,  the  quantity  of  silver  dis- 
solved at  this  pole  being  precisely  equal  to  that  deposited  at  the  opposite 
pole  :  the  silvering  solution  is  always  maintained  at  the  same  strength. 

Platinum. 
Atomic  weight,  197.6.     Symbol,  Pt. 

Platinum  is  found  in  nature  in  flattened  grains  of  varying  sizes, 
more  or  less  alloyed  with  palladium,  rhodium,  ruthenium,  davyum,  and 
iridium.^  It  occurs  in  Brazil,  Peru,  Australia,  and  California.  Russia, 
however,  furnishes  the  largest  supply  of  platinum,  from  the  Ural  Moun- 
tains. It  was  discovered  in  1736  by  Anton  Ulloa  at  Choco,  in  South 
America,  but  in  consequence  of  its  infusibility  and  unworkable  nature  no 
use  was  made  of  it,  and  its  presence  in  mining  products  was  considered 

^  Kichardson's  Treatise  on  Mechanical  Dentistry.  '^  Ibid. 

^  A  group  of  rare  metals  only  found  in  platinum  ores,  and  known  as  the  "  platinum 
metals." 


122  METALS  AND  ALLOYS. 

:i  detriment.  Dr.  Wollaston  devised  the  first  practical  process  of  work- 
ing it,  and  in  1859,  Deville  and  Debray  published  improved  methods  of 
fusing  large  quantities  of  platinum. 

Wollaston's  method,  which  consists  of  a  series  of  chemical  and 
mechanical  processes  of  a  rather  complicated  nature,  may  be  thus  de- 
scribed :  The  ore  is  first  heated  with  nitric  acid  to  dissolve  any  copper, 
lead,  iron,  or  silver.  It  is  then  washed  and  heated  wdth  hydrochloric 
acid  to  remove  any  magnetic  iron  ore  that  may  be  present ;  after  which 
the  ore  is  to  be  treated  with  nitro-hydrochloric  acid  diluted  with  an 
equal  bulk  of  water  to  prevent  the  iridium  generally  present  from  being 
dissolved.  The  proportions  of  acids  are  150  parts  of  hydrochloric  to  40 
parts  of  nitric.  Three  or  four  days'  digestion,  aided  by  gentle  heat,  is 
necessary  to  complete  solution.  The  suspended  matter,  generally  con- 
sisting of  iridium,  is  allowed  to  subside,  when  the  solution  may  be 
siphoned  off. 

Ammonic  chloride  ^  is  next  added  as  a  precipitant,  and  throws  down 
the  yellow  crystalline  ammonio-platinic  chloride,  which  is  readily  de- 
composable by  heat,  yielding  platinum  in  a  finely-divided  state. 

The  liquid  from  which  the  precipitate  is  obtained  will  still  be  found 
to  contain  about  11  parts  of  platinum,  together  with  all  the  associated 
metals.  These  are  all  thrown  down  by  means  of  a  plate  of  zinc  and 
washed  carefully,  and  again  dissolved  in  nitro-hydrochloric  acid.  A 
small  quantity  of  strong  hydrochloric  acid  is  added  to  avoid  precipita- 
tion of  lead  or  palladium,  when  precipitation  of  the  remaining  platinum 
may  be  again  effected  by  ammonic  chloride.  This  precipitate  will  re- 
quire careful  washing  in  cold  water  to  remove  iridium,  which  during  the 
process  forms  a  double  salt  with  the  ammonic  chloride. 

The  next  stage  in  the  operation  consists  in  separating  the  metal  from 
the  ammonia  salt  by  ignition,  and,  as  it  is  important  to  the  success  of 
the  subsequent  working  that  the  precipitate  shall  remain  in  a  finely- 
divided  state,  too  high  a  degree  of  heat  must  be  avoided,  as  otherwise 
cohesion  of  the  particles  will  take  place.  Ignition  is  generally  accom- 
plished by  the  following  means  :  The  precipitate  is  heated  in  a  graphite 
crucible  until  nothing  remains  but  the  finely-divided  platinum.  This  is 
powdered,  should  it  be  found  somewhat  lumpy,  in  a  wooden  mortar 
with  a  wooden  pestle,  sifted  through  a  fine  lawn  sieve,  and  mixed  with 
water  to  the  consistence  of  a  stiff  paste.  This  is  placed  in  a  brass  mould 
with  a  slightly  tapering  cylindrical  cavity  about  7  inches  in  length, 
provided  with  a  loosely-fitting  steel  stopper  which  enters  to  the  depth 
of  a  quarter  of  an  inch.  The  mould  is  first  oiled  and  set  up  in  a  vessel 
of  water.  The  platinum  mud  is  then  introduced,  and  as  it  settles  into 
the  water  air  is  displaced,  and  the  platinum  is  thus  made  to  fill  every 
part  of  the  mould.  The  water  is  allow^ed  to  drain,  and  its  removal  may 
be  aided  by  pressure.  Ultimately,  however,  the  mould  is  placed  in  a 
press  worked  by  a  powerful  lever,  by  which  the  mass  sustains  an  enor- 
mous pressure,  after  which  the  plug  and  the  column  of  platinum  are 
removed  by  gently  tapping  the  mould.  It  is  then  heated  in  a  charcoal 
fire  in  order  to  thoroughly  dry  it  and  to  burn  off  any  adherent  oil. 

The  next  step,  which  depends  upon  the  quality  of  welding  possessed 
by  platinum,  consists  in  heating  the  porous  cylinder  in  a  blast-furnace  to 

'  About  40  parts. 


PLATINUM.  123 

white  heat,  when  it  is  removed,  set  upright  on  an  anvil,  and  hammered 
on  the  ends  in  order  to  weld  the  particles ;  after  which  it  is  coated  with 
a  mixture  of  borax  and  carbonate  of  potash,  and  again  heated  for  the 
purpose  of  removing  traces  of  iron,  which  is  dissolved  by  the  mixture, 
the  latter  being  removed  by  immersion  in  dilute  sulphuric  acid.  The 
bar  of  platinum  is  now  ready  for  use  and  may  be  rolled  or  ham- 
mered. 

It  may  readily  be  surmised  that  so  imperfect  a  means  of  obtaining  a 
solid  bar  of  metal  as  the  latter  part  of  the  operation  just  described  can- 
not always  be  relied  upon  for  the  production  of  a  uniform  and  solid 
specimen  ;  and,  indeed,  platinum  prepared  in  this  way,  though  of  great 
purity,  is  liable  to  blister  upon  its  surface,  this  being  probably  due  to 
minute  globules  of  air  encased  in  the  body  of  the  ingot  during  the  forg- 
ing ;  which  globules  during  the  conversion  of  the  ingot  into  plate  by 
means  of  rollers  are  elongated  and  spread  out  in  the  form  of  blisters. 

The  dry  metallurgic  operations  of  Deville  and  Debray  consist  in 
heating  in  a  reverberatory  furnace  about  2  hundredweight  of  platinum 
ore  with  an  equal  weight  of  galena  (sulphide  of  lead).  When  the  ore  is 
sufficiently  heated  (to  bright  redness)  portions  of  the  galena  are  added 
and  mixed  with  the  ore  by  constant  stirring.  An  equal  quantity  of 
litharge  is  next  added  in  order  to  supply  oxygen  to  the  sulphur  of  the 
lead  ore,  which  passes  off  as  sulphurous  anhydride,  reducing  all  of  the 
lead  Avhich  combines  ^vith  the  platinum.  After  remaining  in  a  state  of 
fusion  for  a  short  time  the  upper  portion  is  ladled  off,  and  Avill  be  found 
to  consist  of  an  alloy  of  lead,  platinum,  and  smaller  portions  of  palla- 
dium and  silver,  the  latter  being  introduced  from  the  galena,  which 
always  contains  more  or  less  silver.  The  heavier  metals  of  the  platinum 
group,  from  their  greater  density,  subside  to  the  bottom. 

Cupellation  is  now  resorted  to  in  order  to  separate  the  platinum  from 
the  lead.  This  consists  of  two  distinct  operations.  The  first  is  performed 
at  the  ordinary  furnace  temperature,  and  is  continued  until  by  loss  of 
lead  the  fusing-point  of  the  remaining  alloy  rises  to  such  an  extent  that 
a  state  of  fusion  can  no  longer  be  maintained.  The  second  and  final 
operation  is  performed  in  an  apparatus  which  serves  the  purpose  of  both 
furnace  and  cupel.  It  is  formed  of  blocks  of  thoroughly-burned  lime. 
In  form  it  may  be  described  as  a  sort  of  basin  or  concavity  with  a  sim- 
ilar piece  for  a  cover.  The  low^er  part  is  intended  for  the  reception  of 
the  metal :  through  the  centre  of  the  upper  portion  or  cover  pass  the 
tubes  for  the  oxyhydrogen  jet,  while  the  lower  portion  is  provided  with 
a  lip  or  spout  for  pouring  the  melted  metal.  The  tubes  which  pass 
through  the  top  for  the  transmission  of  the  two  gases  are  generally 
formed  of  copper,  with  platinum  tips.  The  outer  and  lower  tube  carries 
hydrogen,  while  the  inner  and  upper  one  carries  a  jet  of  oxygen  into  the 
middle  of  the  flame.  The  tubes  are  furnished  with  stopcocks,  so  that 
the  supply  may  be  regulated.  When  the  object  is  merely  to  fuse  some 
scraps  of  platinum,  the  lime  furnace  is  first  put  together,  the  hydrogen 
jet  is  lighted,  oxygen  is  then  turned  on,  and  the  interior  of  the  apparatus 
soon  becomes  heated.  The  platinum  is  then  introduced  in  pieces  through 
a  small  hole  at  the  side,  and  quickly  fuses  after  entering  the  furnace. 

When  used  as  a  cupel  the  lime  absorbs  the  impurities,  and  the  plat- 
inum is  kept  in  a  state  of  fusion  until  all  the  lead  is  oxidized,  when  the 


124 


METALS  AND  ALLOYS. 


metal  may  be  poured  from  the  lime  cupel  into  an  ingot-mould  formed  of 
coke  or  plates  of  lime.  Some  difficulty  may  be  experienced  at  the  moment 
of  pouring  in  consequence'  of  the  dazzling  white  surface  of  the  molten 
lead.  From  seven  to  eight  pounds  may  be  melted  in  this  way  in  from 
forty  to  sixty  minutes. 

Although  such  metals  as  palladium,  osmium,  gold,  silver,  and  lead 
are  volatilized  at  the  intense  heat  used,  it  has  been  found  that  platinum 
obtained  by  the  Deville-Debray  method  is  not  as  pure  as  that  obtained 
by  Wollaston's  plan. 

Properties, — Platinum  is  somewhat  whiter  than  iron.  It  is  exceed- 
ingly infusible,  requiring  the  flame  of  the  compound  blowpipe  (oxyhy- 
drogen)  to  render  it  fluid.     In  both  the  hot  and  cold  states  it  is  exceed- 

FiG.  105. 


Oxyhydrogen  blowpipe 


ingly  malleable  and  ductile,'  It  is  the  heaviest  substance  in  nature,  its 
specific  gravity  being  21,5,  and  it  is  exceeded  in  tenacity  only  by  iron 
and  copper.  No  single  acid  attacks  it,  and  it  is  unaffected  by  air  or 
moisture  at  any  temperature.  It  is  therefore  of  great  value  in  the  con- 
struction of  chemical  vessels. 

At  bright- red  heat  platinum  welds  quite  readily,  and  injured  vessels 
may  be  repaired  in  this  way.  In  the  finely-divided  state,  as  obtained 
by  Wollaston's  process,  it  may  be  made  into  vessels  by  pressing  the  pul- 
verulent metal  into  suitable  moulds,  heating  and  hammering  to  complete, 
the  welding  of  the  particles. 

'  WoUaston,  in  endeavoring  to  substitute  platinum  for  the  spider's  web  usually  em- 
ployed in  micrometei's,  made  platinum  wire  finer  than  had  hitherto  been  obtained.  This 
was  accomplished  by  forming  a  coating  of  silver  upon  a  platinum  wire  and  then  passing 
it  through  the  drawplate,  after  which  he  dissolved  the  silver,  leaving  the  platinum  the 
3  0  00^  of  an  inch  in  diameter,  a  mile  of  which,  notwithstanding  the  high  specific  gravity 
of  the  metal,  would  only  weigh  a  single  grain. 


PLATINUM.  125 

Platinum  possesses  the  remarkable  property  of  inducing  chemical  com- 
bination between  oxygen  and  other  gases.  Even  in  the  compact  condition 
it  possesses  this  quality,  as  demonstrated  by  the  familiar  experiment  of 
suspending  a  coil  of  platinum  wire  in  the  flame  of  a  spirit-lamp,  and 
suddenly  extinguishing  the  flame  as  soon  as  the  metal  becomes  entirely 
heated,  when,  by  inducing  the  combination  of  the  vapor  of  the  spirit  with 
oxygen,  the  wire  will  continue  to  glow.  An  instantaneous  light  appa- 
ratus has  been  made  in  which  a  jet  of  hydrogen  is  thrown  upon  a  ball 
of  spongy  platinum  :  the  latter  induces  combination  between  the  oxygen 
condensed  between  its  pores  and  the  spirit- vapor,  and  ignition  takes 
place. 

Platinum-black,  in  which  the  metal  exists  in  an  exceedingly  fine  state 
of  division,  possesses  this  power  of  promoting  combination  of  oxygen 
with  other  gases  to  the  highest  degree.  In  this  form  it  is  capable  of 
absorbing  eight  hundred  times  its  volume  of  oxygen.  No  combination, 
however,  takes  place  between  the  two,  the  gas  being  merely  condensed 
within  the  pores  of  the  metal  ready  for  combination  with  other  bodies  ; 
hence  if  a  jet  of  hydrogen  be  thrown  upon  a  small  lump  of  this  powder, 
ignition  ensues.  During  the  operation  of  melting,  platinum  absorbs 
oxygen  and  gives  it  off  in  cooling,  "  sputtering  "  as  silver  does  under 
like  conditions. 

The  proper  solvent  for  platinum  is  nitro-hydrochloric  acid,  the 
chlorine  evolved  being  the  active  agent.  Alloyed  with  silver,  however, 
platinum  will  be  dissolved  in  nitric  acid,  and  when  platinum  is  found  in 
gold  as  an  alloy  it  may  be  separated  by  quartation  with  silver. 

Alloys. — Equal  weights  of  platinum  and  gold  afford  a  malleable 
alloy  :  the  brilliancy  of  appearance  characteristic  of  gold  is,  however, 
much  lessened  by  the  admixture.  The  two  metals,  combined  in  the  pro- 
portions of  1  part  of  platinum  to  9.5  of  gold,  form  an  alloy  of  the  same 
density  as  platinum.  An  excess  of  platinum  with  gold  yields  an  alloy 
which  is  infusible  at  ordinary  furnace-heat. 

The  tenacity  of  gold  is  very  greatly  increased  by  admixture  of  plati- 
num, while  at  the  same  time  it  is  rendered  more  elastic. 

Platinum  and  silver  may  be  combined  in  all  proportions,  constituting 
alloys  of  greater  hardness  than  either  of  their  constituents,  while  the 
color  is  between  the  color  of  silver  and  that  of  platinum.  Hot  sul- 
phuric acid  will  dissolve  the  silver  from  an  alloy  of  this  kind,  and  when 
1  part  of  platinum  is  alloyed  with  10  parts  of  silver  both  metals  may 
be  dissolved  by  nitric  acid. 

Platinum  and  mercury  do  not  amalgamate  readily,  and  combination 
can  only  be  effected  by  rubbing  finely-divided  platinum,  such  as  is 
reduced  from  the  ammonio-chloride,  in  a  heated  mortar  with  mercury 
moistened  with  water  acidulated  with  acetic  acid.  By  this  means  an 
unctuous  amalgam  is  obtained  which  has  been  employed  in  platinizing 
metallic  objects  in  a  manner  similar  to  that  known  as  fire-gilding. 

The  use  of  platinum  as  a  constituent  in  alloys  for  dental  amalgams 
has  been  almost  entirely  abandoned.  The  author  found,  as  the  result 
of  a  large  number  of  experiments,  that  it  rendered  the  alloy  very  brittle, 
and,  while  its  presence  seemed  to  retard  amalgamation,  it  increased  the 
capacity  of  the  alloy  for  mercury. 

Iridium  confers  upon  platinum  great  hardness  and  tenacity ;  indeed, 


126  METALS  AND  ALLOYS. 

the  alloy  resulting  from  this  combination  is  so  rigid  that  it  is  with  the 
greatest  difficulty  it  can  be  swaged  into  plates.  It  is,  nevertheless,  an 
alloy  of  great  value  to  the  mechanical  dentist,  as  it  aifords  a  means  of 
obtaining  great  strength  in  artificial  dentures  of  the  "  continuous-gum  " 
class,  and  it  has  been  used  in  the  author's  laboratory  since  1870  in  con- 
nection with  vulcanized  rubber,  the  plate  being  constructed  of  iridio- 
platinum,  with  the  teeth,  single  or  in  sections,  attached  by  means  of 
rubber.  The  swaging  requires  the  use  of  the  zinc  counter-die,  and  when 
the  ridge  is  very  prominent  it  is  best  not  to  attempt  to  carry  the  plate 
entirely  over  it,  rather  allowing  the  rubber  to  take  its  place.  An  arti- 
ficial denture  constructed  in  this  way  has  no  superior  in  point  of  strength 
and  durability. 

Nothing  but  pure  gold  should  be  used  as  a  solder  in  uniting  two 
pieces  of  platinum  or  iridio-platinura.  Indeed,  so  feeble  is  the  union 
between  the  latter  and  an  ordinary  gold  solder  that  two  pieces  united  by 
its  agency  may  be  readily  torn  apart  with  the  pliers.  The  addition  of 
iridium  is  also  of  value  in  the  construction  of  platinum  vessels  for 
experimental  laboratory  use,  as  the  metal  is  thereby  rendered  more 
resistant  to  high  temperatures  and  less  susceptible  to  the  action  of 
chemicals. 

Platinum  combines  with  tin  in  all  proportions,  and  the  resulting  alloy 
is  hard,  brittle,  and  more  or  less  fusible.  Between  the  platinoid  metals 
and  tin,  at  the  moment  of  fusing  together,  phenomena  very  suggestive 
of  true  chemical  union  have  been  observed,  and  if  tin  and  platinum 
foils  be  rolled  together  and  heated  under  the  blowpipe,  combination 
takes  place  explosively.  It  is  in  consequence  of  this  affinity  that  two 
such  metals,  one  of  which  is  infusible  at  ordinary  furnace  temperature, 
while  the  other  is  readily  fusible  at  a  low  degree  of  heat,  may  with  the 
greatest  facility  be  melted  together  to  form  an  alloy.' 

Oxides. — Platinum  unites  with  oxygen  to  form  two  compounds — 
the  monoxide  or  platinous  oxide  (PtO)  and  the  dioxide  or  platinic  oxide 
(Pt02).  The  first  is  obtained  as  a  black  powder  by  digesting  the  dichlo- 
ride  with  caustic  potash.  The  second  (PtOj)  may  be  prepared  by  adding 
barium  nitrate  to  a  solution  of  platinic  sulphate.  Barium  sulphate  and 
platinic  nitrate  are  thus  formed,  and  from  the  latter  caustic  soda  pre- 
cipitates one-half  of  the  platinum  as  platinic  hydrate,  a  bulky  brown 
powder  which,  when  gently  heated,  becomes  black  and  anhydrous.  It 
is  also  formed  when  platinic  chloride  is  boiled  with  an  excess  of  caustic 
soda  and  acetic  acid  added.  It  combines  with  bases  and  dissolves  in 
acids.  Platinic  oxide  with  ammonia  forms  an  explosive  compound 
which  detonates  violently  at  about  400°  F.  Both  oxides  of  platinum  are 
reduced  to  the  metallic  state  by  heating  to  redness. 

Platinic  chloride  (PtCl4)  is  the  most  useful  salt  of  the  metal,  and  is 
the  one  from  which  all  the  platinum  compounds  are  obtained.  It  may 
be  prepared  by  dissolving  scraps  of  platinum  in  a  mixture  of  4  measures 
of  hydrochloric  acid  with  1  of  nitric  acid,  100  grains  of  platinum 
requiring  the  presence  of  2  ounces  of  hydrochloric  acid.  After  com- 
plete solution  the  liquid  is  evaporated  at  a  gentle  heat  to  a  syrupy  con- 
sistence, redissolved  in  hydrochloric  acid,  and  again  evaporated  to  expel 
excess  of  nitric  acid.      The  syrup-like  fluid  solidifies  on  cooling  to  a 

^  See  cliapter  on  "  Alloys." 


IRON.  127 

red-brown  mass  which  is  deliquescent  and  readily  dissolves  in  water  or 
alcohol. 

Spongy  platinum  is  prepared  by  heating  the  yellow  crystalline  pre- 
cipitate obtained  by  the  addition  of  amnionic  chloride. 

Platinous  chloride  (PtCy  may  be  formed  by  heating  platinic  chloride 
to  a  point  somewhat  above  450°  F.  A  very  high  temperature  reduces 
it  to  the  metallic  state. 

Sulphides. — The  compounds  PtS  and  PtS^  are  produced  by  the  action 
of  hydrogen  sulphide,  or  the  hydrosulphide  of  an  alkali  metal,  on  the 
dichloride  and  tetrachloride  of  platinum  respectively.  They  are  both 
black,  insoluble  substances. 

Discrimination  of  Platinum  Salts. — 1st.  A  blackish-brown  pre- 
cipitate, insoluble  in  nitric  or  hydrochloric  acid  singly,  will  be  thrown 
down  by  the  addition  of  hydrogen   sulphide  (H2S). 

2d.  Ammonia  or  potash  throws  down  a  yellow  crystalline  precipitate. 

3d.  A  brown  hydrated  platinic  oxide  is  precipitated  from  the  salts  of 
platinum  by  the  addition  of  soda,  and  it  should  be  remembered  that  the 
precipitate  is  soluble  in  an  excess  of  the  soda. 

4th.  A  deep-brown  color  is  imj)arted  to  solutions  of  platinum  salts 
by  the  addition  of  stannous  chloride,  but  no  precipitate  is  obtained. 

Quantitatively,  platinum  may  be  separated  from  other  metals  with 
which  it  is  likely  to  be  associated  by  precipitating  with  ammonium  chlo- 
ride. This  is  added  to  the  platinum  solution,  followed  by  a  little 
alcohol.  The  precipitate  is  collected,  washed  with  alcohol,  and  dried, 
when  it  is  ready  for  weighing.  Every  100  parts  will  contain  44.28  of 
platinum. 

Iron. 

Atomic  weight,  56.     Symbol,  Fe  (Ferrum). 

Iron  is  present  in  nearly  all  forms  of  rock,  clay,  sand,  and  earth.  It 
is  the  most  widely  diifused  of  the  natural  coloring  ingredients,  and  its 
presence  may  be  readily  distinguished  by  the  color  which  it  imparts.  It 
is  found  in  varying  proportions  in  plants  and  the  bodies  of  animals,  the 
blood  of  the  latter  containing  about  0.5  per  cent,  of  iron  associated  with 
its  coloring  matter. 

Iron  seems  to  have  been  known  very  early  in  the  world's  history,  and 
at  a  remote  period  instruments  of  agriculture  and  war  were  manu- 
factured of  it.^  Its  chief  ores  are  oxides,  carbonate,  and  sulphides. 
Metallic  iron^  is  met  with  in  nature  in  the  meteorites  or  metallic  masses 
of  unknown  origin  which  occasionally  fall  to  the  earth.'^  The  carbonate 
and  oxides  are  the  ores  from  which  iron  is  chiefly  obtained.  Their  re- 
duction— that  of  the  oxide  especially — is  exceedingly  simple,  and  con- 
sists in  merely  heating  them  in  contact  with  carbonaceous  compounds, 
by  which  means  the  metal  is  liberated. 

Properties. — Pure  iron  is  nearly  white  in  color,  extremely  soft  and 

^  Arcbseologists  distinguish  a  Bronze  Age  in  preliistoric  times  intermediate  between 
those  of  Stone  and  Iron. 

^  Metallic  iron,  though  of  exceedingly  rare  occurrence,  has  been  found  at  Canaan  in 
Connecticut,  forming  a  vein  about  2  inches  thick  in  mica  slate. 

^  Isolated  masses  of  soft  iron  sometimes  of  large  dimensions,  have  been  found  upon 
the  surface  of  the  earth  in  South  America;  they  are  supposed  to  have  had  a  similar 
■origin. 


128  METALS  AND  ALLOYS.    , 

tough,  and  has  a  specific  gravity  of  7.8.  Iron  may  be  regarded  as 
possessing  a  greater  number  of  vahiable  qualities  than  any  other  metal ; 
hence  it  occupies  the  highest  place  in  the  useful  arts.  Although  pos- 
sessing nearly  twice  as  much  strength  as  the  strongest  of  the  other 
metals,  it  is  yet  one  of  the  lightest,  and  is  therefore  peculiarly  fitted  for 
use  in  the  constru(;tion  of  bridges,  ships,  etc.  It  is  rendered  so  ductile 
by  heating  that  it  may  be  rolled  into  very  thin  .sheets  or  drawn  into  the 
finest  wire,  and  yet  at  ordinary  temperatures  it  is  the  least  yielding  of 
the  metals  in  common  use,  and  may  always  be  relied  upon  to  afford 
a  rigid  support.  An  iron  wire  one-tenth  of  an  inch  in  diameter  is  capa- 
ble of  sustaining  705  pounds.  It  is  very  difficult  of  fusion,  and 
before  becoming  liquid  passes  through  a  soft  or  pasty  condition. 
Pieces  of  iron  pressed  or  hammered  while  in  this  state  cohere  or  weld 
together. 

The  fusing-point  of  iron  has  been  estimated  at  2900°  F.  It  is  sol- 
uble in  nitric,  dilute  sulphuric,  and  hydrochloric  acids,  but  is  not  much 
affected  by  strong  sulphuric  acid.  Chlorine,  iodine,  and  bromide  attack 
it  readily.  Under  certain  circumstances  it  is  not  acted  upon  by  strong 
nitric  acid.  If  a  piece  of  platinum  wire  be  kept  in  contact  with  it,  it 
will  remain  in  this  acid  for  many  weeks  without  being  acted  upon.  Its 
crystalline  form  is  supposed  to  be  a  cube.  When  rolled  into  bars  or 
drawn  into  wire  it  possesses  a  fibrous  texture,  upon  the  perfection  of 
which  much  of  its  strength  and  value  depends.  It  is  the  most  tenacious 
of  all  the  metals.  At  red  heat  iron  decomposes  water,  evolving  hydro- 
gen, and  is  changed  into  the  black  oxide.  It  is  a  strongly  magnetic 
metal,  but  loses  this  quality  when  heated  to  redness. 

Iron  does  not  oxidize  in  dry  air  at  ordinary  temperatures,  and  it  may 
be  immersed  in  water  from  which  the  air  has  been  carefully  excluded 
without  change.  Contact  with  a  more  electro-positive  metal  will  also, 
prevent  oxidation.  Thus,  fine  steel  instruments  are  sometimes  packed 
for  exportation  by  wrapping  in  thin  sheet  zinc.  For  a  description  of 
the  compounds  of  iron  and  the  reagents  employed  in  its  discrimination 
the  student  is  referred  to  Fownes's  Elementary  Chemistry. 

The  value  of  iron  does  not  depend  alone  upon  its  physical  properties, 
for  it  enters  into  a  large  number  of  compounds  which  are  of  great  use  in 
the  arts,  and  its  chemical  relation  to  carbon  is  such  that  the  addition  of 
a  small  quantity  of  that  element  converts  it  into  steel,  harder  and  more 
elastic  than  iron,  while  a  larger  quantity  of  carbon  produces  cast  iron, 
which  is  so  fusible  that  many  useful  articles  may  be  made  of  it  by  casting. 

Steel. — Herodotus  states  that  among  the  most  precious  gifts  pre- 
sented by  the  Indian  monarch  Porus  to  Alexander  the  Great  was  a 
pound  of  steel,  the  value  of  which  at  that  time  has  been  estimated  at 
about  two  hundred  dollars.  At  a  later  period  the  manufacture  of  steel 
in  its  application  to  warlike  implements  was  carried  to  a  great  state  of 
perfection  in  India  and  in  the  south  of  Europe. 

Steel  differs  from  iron  in  possessing  the  property  of  becoming  very 
hard  and  brittle  if,  when  heated  to  bright  redness,  it  is  suddenly  cooled 
by  being  plunged  into  water.  Steel  is  simply  iron  chemically  combined 
with  the  precise  amount  of  carbon  which  will  produce  the  condition 
referred  to,  together  with  additional  toughness.  It  does  not,  however, 
become  decidedly  steel-like  until  the  carbon  amounts  to  0.3  per  cent. 


IRON.  129 

The  hardest  steel  contains  about  1.2  per  cent,  of  carbon,  and  when  that 
proportion  is  exceeded  it  begins  to  assume  the  properties  of  cast  iron. 

There  are  several  processes  by  which  steel  may  be  produced.  Bars 
of  iron  imbedded  in  charcoal  powder  in  a  suitable  crucible  or  chest  made 
of  some  substance  capable  of  resisting  the  fire  are,  after  several  hours' 
exposure  to  heat,  converted  into  steel,  the  iron  taking  up  the  requisite 
amount  of  carbon.  The  product  of  this  operation  is  called  "  blistered 
steel,"  and  is  far  from  uniform  either  in  composition  or  texture,  as  por- 
tions of  the  bars  thus  produced  will  be  found  to  contain  more  carbon 
than  others,  and  the  interior  to  be  more  or  less  porous.  For  the  pur- 
pose of  improving  its  quality  the  bars  are  cut  into  short  lengths,  made 
up  into  bundles,  heated  to  the  welding-point,  and  placed  under  a  power- 
ful tilt-hammer,  which  consolidates  each  bundle  into  one  mass.  This  is 
called  "  shear  steel." 

Fusing  and  casting  steel  is  another  process  for  the  treatment  of  the 
blistered  form,  by  which  is  produced  the  best  and  most  homogeneous 
variety.  It  consists  in  fusing  about  30  pounds  of  broken  fragments  of 
blistered  steel  in  a  plumbago  crucible,  the  surface  being  protected  from 
oxidation  by  glass  melted  upon  it.  When  perfectly  fluid  the  steel  is  cast 
into  ingots,  and  when  it  is  desirable  to  form  a  very  large  ingot  several 
crucibles  are  simultaneously  emptied  into  the  same  mould.  Cast  steel  is 
superior  in  density  and  hardness  to  shear  steel,  and  is  the  form  best 
adapted  to  the  manufacture  of  fine  cutting  instruments.  It  is,  however, 
somewhat  brittle  at  red  heat,  and  much  care  and  skill  is  required  in 
forging  it.  The  addition  to  it  while  fused  of  1  part  of  a  mixture  of 
charcoal  and  oxide  of  manganese  affords  a  fine-grained  steel,  which  may 
be  cast  into  a  bar  of  wrought  iron  in  the  ingot-mould,  in  order  that  the 
tenacity  of  the  iron  may  be  an  offset  to  the  brittleness  of  the  steel  when 
forged  together,  while  it  affords  an  economical  compound  in  the  manu- 
facture of  cutting  implements,  the  iron  forming  the  back  and  the  steel 
the  edge  of  the  instrument. 

Bessemer '  steel  is  produced  by  forcing  atmospheric  air  into  melted 
cast  iron.  The  carbon,  which  is  oxidized  more  readily  than  the  iron, 
escapes  in  the  form  of  carbon  monoxide,  combustion  of  which  takes 
place  on  coming  in  contact  with  atmospheric  air,  and  sufficient  heat  is 
thus  generated  to  keep  the  temperature  above  the  melting-point  of  steel 
during  the  operation.  The  current  of  air  is  stopped  as  soon  as  the  decar- 
buration  has  progressed  far  enough,  when  a  quantity  of  white  pig  iron 
containing  manganese  is  added  to  the  fluid  metal  for  the  purpose  of 
assisting  the  separation  of  gas  from  the  melted  metal.  It  is  then  ready 
for  casting. 

Some  New  Iron  Alloys. — The  combinations  of  iron  with  aluminum, 
chromium,  copper,  manganese,  nickel,  silicon,  and  tungsten  constitute  a 
class  of  alloys  which  are  essentially  new  and  are  termed  steels,  and  are 
usually  designated  with  a  prefix  of  the  name  of  the  particular  element 
present,  as  nickel  steel,  chrome  steel,  etc. 

Aluminum  Steel. — The  addition  of  aluminum  slightly  increases 
the  tensile  strength,  and  proportionately  the  elastic  limit,  in  rolled  and 
cast  steel  when  the  amount  added  is  not  greater  than  1  per  cent. 

^  For  other  methods  of  producing  steel  see  Percey's,  Phillips',  or  Makins'  works  on 
metallurgy 


130  METALS  AND  ALLOYS. 

Chrome  Steel. — Chromium  increases  the  hardness,  tensile  strength, 
and  elastic  limit  of  iron,  but  lessens  its  weldability.  Ferro-chrome  is 
made  by  heating  the  mixed  oxides  of  iron  and  chromium  in  brasqued 
crucibles,  adding  powdered  charcoal  and  fluxes.  Chrome  steel  is  then 
produced  from  ferro-chrome  by  melting  it  with  wrought  iron  or  steel  in 
graphite  crucibles.  It  has  been  stated  that  the  presence  of  chromium 
in  steel  renders  it  more  susceptible  to  oxidation  by  exposure  to  air  and 
moisture  than  ordinary  steel.  It  w^as  thought  that  chrome  steel  would 
admirably  fill  certain  special  requirements  where  great  hardness  and 
toughness  is  needed,  as  the  manufacture  of  dental  instruments,  pro- 
jectiles, cuirasses,  etc.,  but  there  are  other  steel  alloys  coming  into  use 
which  are  so  much  better  that  it  is  probably  only  a  question  of  time 
when  it  will  be  superseded. 

Copper  Steel. — M.  Henry  Schneider  of  Creusot,  France,  obtained 
patents  for  the  manufacture  of  alloys  of  iron  and  copper  and  steel  and 
copper.  These  alloys  can  be  made  in  crucible,  cupola,  or  open-hearth 
furnace.  The  furnace  is  charged  with  copper  scraps  and  cast  iron  mixed 
between  layers  of  coke,  or,  if  a  cupreous  coke  be  employed,  then  the  cast 
iron  is  laid  in  alternate  layers  with  it,  and  a  layer  of  anthracite  is  laid 
over  the  whole.  The  alloy  thus  formed  contains  generally  from  5  to  20 
per  cent,  of  copper,  according  to  the  purpose  for  which  it  is  to  be  em- 
ployed, and  it  is  remarkable  for  its  great  strength,  tenacity,  and  malle- 
ability— properties  which  may  still  further  be  developed  by  chilling  or 
tempering. 

Nickel  Steel. — United  States  patents  415,657  and  415,655, 
NovAnber  19,  1889,  were  granted  M.  Henry  Schneider  of  Creusot, 
France,  for  the  manufacture  of  alloys  of  cast  iron  and  nickel  and  steel 
and  nickel,  respectively.  The  alloy  of  cast  iron  and  nickel  contains 
from  5  to  30  per  cent,  of  nickel,  and  is  remarkable  for  its  great  elasticity 
and  strength — properties  which  admit  of  further  development  by  the 
usual  chilling  or  tempering. 

The  alloy  of  steel  and  nickel  usually  contains  about  5  per  cent,  of 
nickel,  and  is  especially  suitable  for  use  in  the  construction  of  ordnance, 
armor-plate,  gun-barrels,  and  projectiles.  Some  specimens  of  nickel 
steel  recently  produced  by  Carnegie,  Phipps  &  Co.  for  the  U.  S.  Navy 
Department,  containing  -^^  per  cent,  of  nickel,  showed,  when  tested,  the 
following  results  :  Elastic  limit,  59,000  and  60,000  pounds  per  square 
inch  ;  ultimate  tensile  strength,  100,000  and  102,000  pounds  per  square 
inch. 

It  is  stated  that  the  presence  of  manganese  in  nickel  steel  is  most 
important,  as  it  appears  that  without  the  aid  of  manganese  in  proper 
proportions  the  best  results  could  not  be  obtained.  Nickel  steel  is  said 
to  be  less  liable  to  corrode  in  salt  water  than  ordinary  steel,  which,  it 
may  be  proper  to  observe  in  this  connection,  is  more  readily  acted  upon 
by  sea-water  than  are  the  more  impure  grades  of  iron. 

The  success  of  the  nickel-steel  armor-plate  at  the  recent  test  by  the 
U.  S.  Navy  Department,  in  which  the  nickel-steel  plates  alone  withstood 
the  eight-inch  chrome-steel  projectiles  without  cracking,  has  had  a  most 
important  influence  upon  the  manufacture  of  that  alloy. 

Manganese  Steel. — The  maximum  of  strength,  toughness,  and 
hardness  is  probably  reached  in  this  alloy  when  about  15  per  cent,  of 


IRON.  131 

manganese  is  added  to  steel.  The  chief  obstacle  to  the  commercial  pro- 
duction of  manganese  steel  is  its  extreme  hardness.  The  working  of 
some  of  the  grades  of  this  material  by  the  ordinary  methods  is  almost 
impossible. 

Manganese  steel  is  usually  made  by  adding  ferro-manganese  to  molten 
Bessemer  or  open-hearth  steel.  The  extreme  point  of  brittleness  in  this 
alloy  occurs  in  specimens  containing  from  4  to  5  per  cent,  of  manganese. 
Extremes  of  atmosphere,  heat  or  cold,  do  not  appear  to  aifect  the  prop- 
erties of  manganese  steel.  When  a  piece  of  it,  heated  sufficiently  to  be 
seen  red  hot  in  a  dark  room,  is  plunged  into  cold  water,  it  becomes  soft 
enough  to  be  easily  filed.  Hardness  is  then  restored  by  reheating  to  a 
bright  red  and  cooling  in  air. 

Hardening  and  Tempering. — Hardening  of  ordinary  carbon  steel  is 
effected  by  subjecting  the  object  to  extremes  of  temperature.  The  com- 
mon practice  is  to  first  coat  the  surface  of  the  metal  with  some  carbon- 
aceous substance,  such  as  soap,  to  prevent  scaling  and  oxidation  of  the 
surface.  Ferrocyanide  of  potassium  has  also  been  used  for  surface- 
hardening.  This  salt  contains  cyanogen  (CgNg),  a  gas  consisting  of  12 
parts  by  weight  of  carbon  and  14  of  nitrogen.  This  is  decomposed  at 
the  high  temperature  which  is  employed,  and  supplies  carbon  to  the  sur- 
face of  the  metal.  This  salt  is,  however,  better  suited  to  the  process 
known  as  case-hardening,  while  in  retempering  dental  instruments  soap 
answers  every  requirement. 

The  metal  is  next  heated  to  the  point  of  full  redness,  and  then  sud- 
denly plunged  into  cold  water,  oil,  tallow,  or  mercury,  or,  in  the  case 
of  small  objects,  is  merely  placed  on  a  large  piece  of  cold  metal.  It  is 
thus  rendered  very  hard,  while  at  the  same  time  it  increases  slightly  in 
volume. 

If  hardened  steel  be  heated  to  redness  and  allowed  to  cool  slowly,  it 
is  again  converted  into  soft  steel,  but  it  may  be  proportionately  reduced 
by  heating  to  a  temperature  short  of  redness,  the  proper  point  of  which 
may  be  ascertained  by  noting  certain  colors  which  appear  on  the  ground 
or  brightened  surface  of  a  steel  instrument  when  held  over  a  flame.  This 
discoloration  is  due  to  the  formation  of  a  thin  film  of  oxide,  and  as  the 
temperature  rises  the  film  becomes  thicker  and  darker  and  the  instrument 
softer.  It  is  therefore  necessary  to  plunge  the  instrument  into  a  cold 
menstruum  the  instant  the  color  indicating  the  desired  degree  of  hard- 
ness is  reached.  The  following  table  indicates  the  tempering  heats  of 
various  instruments : 


Temperature. 

Color. 

Use. 

430°  to  450°  F. 
470°  F. 
490°  F. 
510°  F. 
520°  F. 
530°  to  570°  F. 

Light  yellow. 

Medium  yellow. 

Brown-yellow. 

Brown-purple. 

Purple. 

Blue. 

Enamel  chisels. 

Excavators. 

Pluggers. 

Saws,  etc. 

Wood-cutting  tools. 

When  elasticity  is  desired. 

In  "'  letting  down  "  or  tempering  dental  instruments  the  flame  of  a 
spirit  lamp  may  be  employed,  the  instrument  being  placed  in  it :  the  flame 
should  strike,  however,  some  distance  from  the  cutting  end,  and  when  the 
proper  color  reaches  the  end  it  should  be  thrust  into  water.     Another 


132  METALS  AND  ALLOYS 

very  convenient  means  of  effecting  the  same  result  consists  in  heating  an 
iron  bar  to  redness  at  one  end,  and  then  fixing  it  in  a  vise.  The  object 
to  be  tempered  is  placed  in  contact  with  this  until  the  desired  tint 
appears. 

Steel  when  fractured  shows  a  fine  silky  appearance  of  the  broken  sur- 
face. Overheating,  however,  deprives  it  of  carbon,  when  the  fractured 
surface  presents  a  coarse  granular  condition,  showing  that  it  is  unfit  for 
use  for  fine  cutting  instruments. 

Case-hardening  consists  in  conferring  the  hardness  of  steel  upon  the 
external  surface  of  iron  objects  which  are  to  be  subjected  to  considerable 
wear,  such  as  gunlocks,  etc.,  and  is  accomplished  by  heating  them  in 
some  substance  rich  in  carbon  (such  as  bone-dust,  cyanide  of  potassium, 
etc.),  and  afterward  chilling  in  water.  The  body  of  the  piece  so  treated 
retains  the  toughness  of  iron. 

Malleable  iron  is  produced  by  a  process  the  reverse  of  that  employed 
in  case-hardening.  It  consists  in  heating  the  object,  usually  made  of 
cast  iron  (when  great  softness  and  tenacity  are  required),  for  some  hours 
in  contact  with  oxide  of  iron  or  manganese,  by  which  its  carbon  and 
silicon  are  removed. 

A  steel  instrument  may  be  readily  distinguished  from  iron  by  placing 
a  drop  of  nitric  acid  upon  it,  a  dark  stain  being  produced  upon  steel  by 
the  action  of  the  carbon. 


Lead. 

Atomic  weight,  207.     Symbol,  Pb  (Plumbum). 

The  reduction  of  lead  is  effected  in  a  reverberatory  furnace  in  which 
the  broken  lead  ore  (galena)  is  roasted  at  a  dull-red  heat,  by  which 
means  the  sulphide  becomes  oxidized  and  converted  into  sulphate.  At 
this  stage  of  the  operation  the  contents  of  the  furnace  are  thoroughly 
mixed  and  the  temperature  raised,  which  causes  the  sulphide  and  sul- 
phate to  react  upon  each  other,  producing  sulphurous  oxide  and  metallic 
lead. 

Lead  is  the  softest  metal  in  common  use,  and  may  be  said  to  be  the 
least  tenacious.  In  fusibility  it  also  surpasses  all  other  metals  com- 
monly employed  in  the  metallic  state  except  tin,  the  fusing-point  of  lead 
being  617°  F.  =  325°  C.  It  is  quite  malleable  and  ductile,  and  will 
admit  of  being  rolled  into  thin  sheets  or  foil,  in  which  form  it  was  at 
one  time  much  used  in  filling  teeth.  Its  chief  use  in  the  dental  labora- 
tory consists  in  the  formation  of  counter-dies. 

Alloys. — Lead  unites  with  tin  in  all  proportions,  the  resulting  alloys 
being  more  tenacious  and  fusible  than  either  constituent.  By  the  addi- 
tion of  bismuth  the  fusing-point  is  reduced  below  the  boiling-point  of 
water. 

Lead  amalgamates  readily  with  mercury,  condensation  accompanying 
the  union.  The  noble  metals  are  all  rendered  brittle  and  unworkable  by 
the  presence  of  lead.  There  are  some  properties  peculiar  to  alloys  of 
lead  and  silver  Avhich  are  turned  to  advantage  in  the  separation  of  silver 
from  lead  when  it  occurs  as  a  native  alloy.  Lead  combined  with  a  con- 
siderable quantity  of  silver  will  remain  fluid  at  a  lower  temperature  than 


COPPER. 


133 


other  specimens  containing  a  smaller  percentage,  thus  affording  an 
opportunity  for  the  poorer  lead  to  crystallize,  when  it  is  ladled  out.^ 

The  smallest  proportion  of  lead  in  gold  will  greatly  impair  the 
ductility  of  the  latter.  Makins  states  that  "■  Hatchett  found  that  yw2^ 
of  lead  destroyed  the  coining  qualities  of  gold."  Gold  reduced  to 
standard  fineness  by  lead  is  light-yellow  in  color  and  quite  brittle.  The 
contents  of  the  dentists'  gold-drawer  are  always  liable  to  contamination 
by  small  pieces  of  lead,  the  latter  being  much  used  in  the  form  of  thin 
sheets  in  the  making  of  patterns  by  which  the  gold  or  silver  plate  is  cut. 
As  the  working  qualities  of  the  precious  metals  are  seriously  impaired 
by  its  presence,  means  should  be  instituted  to  ensure  its  complete  re- 
moval. This  may  be  accomplished  by  cupellation,  or  by  melting  the 
gold  or  silver  in  a  crucible  and  adding  nitrate  of  potassium  when  the 
point  of  complete  fusion  has  been  reached. 

Lead  and  platinum,  like  tin  and  platinu«i,  appear  to  possess  con- 
siderable affinity  for  each  other,  and  an  alloy  of  the  two  can  be  formed 
at  a  comparatively  low  temperature. 

An  alloy  of  lead  and  platinum  is  very  hard  and  brittle.  With  palla- 
dium also  lead  forms  a  very  hard  and  brittle  alloy. 

The  most  valuable  alloys  of  lead  are  those  which  it  forms  with  tin, 
antimony,  and  bismuth,  constituting  solders,  pewter,  type-metal,  etc. 

Soft  solders  usually  consist  of  lead  and  tin  in  various  proportions. 
Bismuth  and  sometimes  cadmium  are  added  when  a  more  fusible  solder 
is  required.  Metallic  tin  is  used  alone  in  some  cases,  as  in  the  soldering 
of  fine  utensils  of  tin-plate.  Lead  is  also  soldered  to  lead  by  simply 
melting  the  edges  by  means  of  a  blowpipe  flame.  This  is  called  autog- 
enous soldering. 

Soft  solders  are  termed  common,  medium,  or  best  according  to  the 
amount  of  tin  entering  into  their  composition.  Fine  or  best  solder  is 
largely  used  for  uniting  objects  composed  of  britannia  metal,  tin-plate, 
brass,  etc.  An  alloy  of  1  part  of  tin  to  2  parts  of  lead  is  the  common 
solder  used  by  plumbers. 

The  composition  of  the  different  kinds  of  soft  solder  is  given  in  the 
following  table  •? 


Tin. 
1  . 
1  . 
1  . 
1  . 
1  . 


Lead. 
.  10 


Tin. 

2 
3 
4 

5 


Lead. 
.  1 
.  1 
.  1 
.  1 
.  1 


For  the  discrimination  of  lead  the  student  is  referred  to  Fownes's  or 
other  standard  works  on  chemistry. 


Copper. 
Atomic  weight,  63.4.     Symbol,  Cu  (Cuprum). 

Copper  is  a  metal  with  which  mankind  has  been  acquainted  from  the 
most  remote  periods,  and  probably  the  first  metallic  compound  employed 
was  copper  alloyed  with  tin  (bronze),  of  which  many  relics  in  the  form 

^  See  chapter  on  "Silver."  ^  Mixed  Metals,  Hiorns. 


134  METALS  AND  ALLOYS. 

of  arms,  ornaments,  and  domestic  implements,  evidently  belonging  to  an 
early  period  in  prehistoric  times,  are  still  to  be  found.^  It  is  probable, 
however,  that  the  production  of  the  pure  metal  is  an  operation  of  a  more 
recent  date. 

Copper  ores  are  found  in  many  parts  of  America  and  Europe.  In 
some  parts  of  the  United  States  the  native  metal  is  found  in  immense 
masses  many  hundred  pounds  in  weight,  sometimes  slightly  intermixed 
with  silver.  Nothing  is  certainly  known  of  the  origin  of  these,  but  they 
are  supposed  to  have  been  formed  from  the  cupric  sulphide,  which  by 
exposure  to  air  and  moisture  was  converted  into  sulphate,  and  then,  by 
electro-chemical  agency,  reduced  to  the  metallic  state. 

There  are  several  ores  which  yield  copper.  The  one  most  commonly 
employed,  however,  is  copper  pyrites,  a  combination  of  sulphide  of 
copper  and  iron.  The  blue  and  green  carbonates,  known  respectively 
as  azurite  and  malachite,  are  beautiful  minerals  extensively  used  in 
Russia  and  Bohemia  in  the  manufacture  of  ornamental  objects.  They 
contain  upward  of  50  per  cent,  of  copper. 

The  process  of  obtaining  copper  from  an  ore,  such  as  copper  pyrites, 
may  be  thus  briefly  described  :  The  ore  is  heated  in  a  reverberatory 
furnace  for  the  purpose  of  converting  the  iron  sulphides  into  oxide.  The 
copper,  which  remains  unadulterated,  is  then  heated  with  a  siliceous  sand, 
which  combines  with  the  iron  oxide  to  form  a  slag  and  separates  from 
the  heavier  (copper)  compounds.  By  repeating  this  process  the  iron  is 
finally  gotten  rid  of,  when  the  copper  sulphide  begins  to  decompose  in 
the  flame-furnace,  parting  with  its  sulphur  and  absorbing  oxygen.  The 
resulting  oxide  is,  however,  reduced  by  the  aid  of  carbonaceous  matter 
and  a  high  degree  of  heat. 

Properties. — Pure  copper  may  be  obtained  by  decomposing  a  solution 
of  pure  sulphate  of  copper  in  the  galvanic  current.  If  the  negative 
wire  be  attached  to  a  copper  plate  immersed  in  the  solution,  the  pure 
metal  will  be  deposited  on  it,  and  may  be  readily  stripped  off. 

The  chief  value  of  copper  in  the  useful  arts  is  due  to  its  great 
malleability,  in  which  quality  it  is  only  exceeded  by  gold  and  silver.  It 
fuses  at  about  2000°  F.  It  expands  in  solidifying,  and  absorbs  oxygen 
very  much  in  the  same  manner  as  does  silver  under  similar  conditions. 
In  tenacity  copper  ranks  next  to  iron,  as  a  copper  wire  of  one-tenth  of 
an  inch  in  diameter  will  support  about  385  pounds.  Its  power  of  con- 
ducting electricity  is  nearly  equal  to  that  of  silver,  while  in  the  trans- 
mission of  heat  it  is  surpassed  only  by  silver  and  gold.  It  is  readily 
soluble  in  nitric  acid,  but  in  sulphuric  acid  only  with  the  assistance  of 
heat.  Hydrochloric  acid  attacks  it  slowly,  and  in  vacuo  is  inactive. 
The  specific  gravity  of  copper  is  8.93.  For  the  compounds  of  copper 
with  the  non-metallic  elements  the  student  is  directed  to  Fownes's, 
Bloxam's,  and  other  works  on  chemistry. 

Amalg-ams. — Copper  does  not  readily  unite  with  mercury  without 
the  assistance  of  heat.  There  is,  however,  an  amalgam  of  pure  copper 
and  mercury  extensively  used  in  Europe  under  the  name  of  Sullivan's 
amalgam.  Its  preparation  is  as  follows  :  Pure  copper  in  a  finely-divided 
state  is  obtained  by  boiling  a  concentrated  solution  of  cupric  sulphate 

'  The  epoch  marked  by  the  use  of  bronze  is  known  as  archaeological  chronology  as  the 
Bronze  Age. 


COPPER.  135 

with  distilled  zinc  until  the  blue  color  of  the  salt  disappears,  when  the 
zinc  should  be  removed.  The  copper,  which  will  be  found  in  a  pul- 
verulent mass  at  the  bottom  of  the  vessel,  should  be  washed  with  dilute 
sulphuric  acid,  subsequently  in  hot  distilled  water,  and  dried.  It  is  then 
moistened  with  a  solution  of  nitrate  of  mercury,  by  which  means  the 
copper  becomes  completely  coated  with  mercury.  The  mercury  is  then 
added  to  it  to  the  extent  of  twice  the  weight  of  copper  (3  of  copper  to  6 
of  mercury).  It  is  then  rolled  into  small,  lozenge-shaped  pieces,  which 
become  quite  hard,  and  are  supplied  to  the  profession  in  bottles  con- 
taining an  ounce  or  more.  This  amalgam  possesses  the  property  of 
softening  with  heat  and  again  hardening,  and  when  employed  as  a  filling 
material  one  of  the  lozenge-shaped  pieces  is  placed  in  a  small  iron  spoon 
made  and  sold  for  the  purpose,  and  heated  over  the  flame  of  a  spirit- 
lamp  until  small  globules  of  mercury  are  driven  to  the  surface,  when  it 
is  placed  in  a  small  glass  or  porcelain  mortar  and  rubbed  into  a  smooth 
paste.  Some  recommend  washing  with  a  weak  solution  of  sulphuric 
acid  or  soap  and  water,  and  lastly  with  clean  water  alone  to  remove  the 
last  traces  of  either  acid  or  soap,  and  finally  squeezing  through  chamois 
leather  to  exclude  surplus  of  mercury,  when  it  is  ready  to  be  introduced 
into  the  cavity.  It  requires  several  hours  to  harden.  Mr.  Fletcher 
says  of  this  amalgam  that  "  it  is  an  absolutely  permanent  filling,  as  the 
copper  salts  permeate  and  perfectly  preserve  the  tooth."  It  is  said  to  be 
quite  insoluble  in  the  mouth.  It,  however,  becomes  intensely  black,  and 
imparts  a  most  objectionable  stain  to  the  teeth. 

According  to  Watts'  Chemical  Dictionary,  the  specific  gravity  of 
pure  copper  amalgams  is  the  same  after  hardening  as  before ;  "  hence  the 
presence  of  copper  in  amalgam  alloys  lessens  their  contractibility." 

It  is  said  ^  that  the  tendency  of  copper  amalgam  to  discolor  may  be 
lessened  by  careful  attention  to  its  j)reparation.  The  older  way  of  pre- 
paring it  was  by  precipitating  copper  from  a  solution  of  cupric  sulphate, 
with  mercury  at  the  bottom  of  the  vessel  that  contained  it,  by  stirring 
the  fluid  with  a  bar  of  zinc ;  but  a  better  way,  and  one  now  employed, 
is  to  substitute  a  clean  iron  bar  for  the  zinc,  and  leave  it  from  twelve  to 
twenty-four  hours  in  a  jar  containing  the  solution.  The  iron  bar  becomes 
covered  with  a  dull-red  flocculent  precipitate  of  copper.  When  a  suf- 
ficient quantity  of  the  precipitate  is  formed  it  is  collected  into  another 
jar,  and  well  washed  with  a  stream  of  cold  water  until  it  becomes  quite 
clean.  It  is  then  ground  in  a  mortar  until  it  begins  to  amalgamate,  the 
amalgamation  being  hastened  by  hot  water  slightly  acidulated  with  sul- 
phuric acid,  which  will  also  remove  traces  of  iron.  It  should  next  be 
washed  in  liquor  ammonia  to  neutralize  traces  of  acid,  and  must  then  be 
thoroughly  triturated  in  a  mortar  until  thorough  amalgamation  has  been 
effected.  The  amalgam  should  be  rolled  into  small  pellets  and  allowed 
to  set  for  twenty-four  hours  before  using. 

The  expectations  of  valuable  therapeutic  qualities  in  copper  amal- 
gams have  not  been  realized.  Dr.  C  D.  Cook  and  W.  St.  G.  Elliott 
of  London  found  by  experiment  that  copper  amalgams  shrunk  more  than 
simple  alloys  of  tin  and  silver,  and  the  opinion  seems  to  be  gaining 
ground  among  those  who  have  recently  somewhat  eagerly  adopted  it  as  a 
filling  material  that  it  is  a  very  uncertain  agent,  and  that,  "  whatever 
^  Mr.  E.  P.  Collett,  British  Journal  of  Dental  Science,  April  15,  1890. 


136  METALS  AND  ALLOYS. 

antiseptic  influence  it  has,  it  does  not  prevent  decay  from  beginning  and 
progressing  directly  in  contact  with  it."  ^ 

Alloys. — Copper  unites  readily  with  all  other  metals,  and  many  of 
the  resulting  alloys  are  of  great  value  in  the  industrial  arts — of  even 
more  value  than  the  pure  metal.  It  is  added  to  silver  for  the  purpose 
of  conferring  sufficient  hardness  upon  the  latter  to  enable  it,  in  the  form 
of  coin  or  plate,  to  withstand  the  attrition  to  which  such  articles  are 
exposed. 

The  formation  of  a  perfectly  uniform  alloy  of  silver  and  copper  is  a 
process  attended  with  some  uncertainty,  owing  to  a  tendency  on  the  part 
of  the  copper  to  separate  and  pass  oiF  toward  the  edges  as  the  ingot 
solidifies.  Thus,  in  silver  coins  one  portion  of  the  piece  will  frequently 
be  found  to  contain  more  copper  than  another. 

The  decimal  proportions  of  copper  and  silver  in  standard  silver  (coin) 
of  several  different  nationalities  are  as  follows  : 

Of  the  United  States silver  900,  copper  100 

"   France      "      900,       "       100 

"   England ■•....       "      925,       "         75 

"   Indian  rupees '■      947,       "         53 

"   Germany — Prussian  thalers "      811,        "       189 

"  "  Prussian  silver  groschen "      283,       "       717 

The  properties  conferred  upon  gold  by  the  addition  of  copper  are 
similar  to  those  imparted  to  silver.  These  have  already  been  alluded  to 
on  page  — .  The  decimal  proportions  in  the  gold  coins  of  the  United 
States,  France,  and  Holland  are — gold  900,  copper  100  ;  while  English 
coins  are  composed  of  916.6  of  gold  and  83.3  of  copper.  In  coin-gold 
malleability  is  not  greatly  interfered  with.  Gold  may,  however,  be 
rendered  brittle  by  large  proportions  of  copper  or  when  the  latter  is 
impure. 

Copper  and  platinum  form  an  alloy,  when  the  proportions  are  equal, 
of  nearly  the  same  specific  gravity  and  color  as  gold.  Copper  also 
unites  with  palladium  to  form  a  light,  brassy  alloy.  By  admixture  with 
lead  or  bismuth  copper  is  rendered  quite  brittle.  The  principal  alloys 
in  which  it  forms  a  leading  ingredient  are  brass,  bronze,  and  German 
silver. 

The  alloys  manufactured  under  the  name  of  German  silver  or  nickel 
silver  consist  usually  of  nickel,  copper,  and  zinc.  In  some  cases  a  little 
cobalt  is  present,  and  from  1-3  per  cent,  of  lead  is  sometimes  added 
when  the  alloy  is  to  be  used  for  cast  work.  The  formulas  for  the  com- 
position of  German  silver  are  very  numerous,  but  probably  the  best 
quality  of  the  alloy  is  made  of  the  following  proportions : 

Copper 46 

Nickel 34 

Zinc 20 

"  The  German  method  of  mixing  the  different  metals  in  the  forma- 
tion of  nickel  silver,  as  given  by  Hiorns,^  is  as  follows :  The  zinc 
and  nickel  to  be  used  for  a  certain  quantity  of  copper  are  divided  into 

1  Dr.  Howe  in  discussions  of  J.  Allen  Osmun's  paper  entitled  "Some  Observations  on 
the  Use  of  Copper  Amalgams,"  read  before  the  New  York  Odontological  Society,  pub- 
lished in  the  International  Dental  Journal  for  July,  1892.  ^  Mixed  Metals,  p.  224. 


COPPER.  137 

three  equal  portions.  On  the  bottom  of  a  graphite  crucible,  capable  of 
holding  22  pounds  of  the  alloy,  is  placed  a  layer  of  copper,  and  upon 
this  a  layer  of  zinc  and  nickel ;  upon  this  another  layer  of  copper  is 
placed,  and  so  on  until  all  the  copper  is  in  the  crucible.  One-third  each 
of  zinc  and  nickel  is  retained  for  future  addition.  The  contents  of  the 
crucible  are  then  covered  with  charcoal  powder,  and  the  metals  melted 
in  an  ordinary  casting  furnace.  When  the  contents  are  supposed  to  be 
liquefied  an  iron  rod  is  inserted,  and  if  the  whole  is  thoroughly  fused, 
it  is  then  vigorously  stirred.  The  remaining  zinc  and  nickel  are  then 
added  in  portions  at  a  time,  and  the  whole  well  stirred  after  each  addi- 
tion, a  brisk  fire  being  maintained  to  prevent  chilling  of  the  alloy  by  the 
freshly-added  metals.  After  the  introduction  of  the  last  portion  an 
additional  piece  of  zinc  is  thrown  into  the  crucible  to  compensate  for 
loss  of  zinc  by  volatilization.  If  the  alloy  is  intended  for  rolling,  it 
should  be  kept  liquid  for  some  time  longer  before  casting,  keeping  the 
surface  well  covered  with  charcoal." 

Aluminum  bronze  is  formed  of  pure  copper  alloyed  with  from  2.5  to 
10  per  cent,  of  aluminum.  It  is  quite  malleable,  and  has  a  fine,  rich 
golden  color.  Phosphor  bronze  is  copper  combined  with  from  3  to  15 
per  cent,  of  tin  and  from  \  to  2^  per  cent,  of  phosphorus.  Other 
metals,  such  as  silver,  nickel,  cobalt,  antimony,  and  bismuth,  frequently 
enter  into  the  composition  of  bronzes. 

Copper  in  small  quantities  (from  5  to  7  per  cent.)  is  said  by  Mr. 
Fletcher  to  confer  upon  amalgams  the  quick-setting  property  obtained 
by  the  addition  of  platinum.  It  is,  however,  considered  inferior  to 
platinum  as  a  constituent  in  dental  alloys ;  but  in  the  absence  of  plati- 
num amalgams  are  improved  by  the  addition  of  a  small  proportion  of 
copper. 

It  is  stated^  that  an  alloy  of  tin  10,  silver  8,  gold  1,  copper  1  has 
been  extensively  used  (in  England  probably)  under  the  names  of  gold 
amalgam  and  platinum  amalgam. 

Hydrogen  sulphide  (HgS)  and  ammonium  sulphide,  when  added  to  a 
copper  solution,  aiFord  a  brownish-black  cupric  sulphide. 

Caustic  potash  throws  down  a  pale-blue  precipitate  of  cupric  hydrate, 
which  changes  to  a  blackish-brown  anhydrous  oxide  on  boiling.  Am- 
monia also  gives  a  blue  precipitate,  soluble  in  excess,  affording  a  deep 
purplish-blue  solution. 

Potassium  ferrocyanide  gives  a  red-brown  precipitate  of  cupric  ferro- 
cyanide.  It  may  also  be  detected  in  very  weak  solutions  by  placing  a 
drop  on  a  slip  of  clean  platinum-foil.  A  point  of  zinc  is  then  dipped 
in  so  as  to  touch  the  foil,  and  instantly  a  spot  of  reduced  copper  appears. 

A  green  line  is  imparted  to  the  oxidizing  flame  of  the  blowpipe  when 
a  copper  salt  is  heated  in  it.  It  also  communicates  a  green  tint  to  borax 
when  heated  with  it. 

There  are  several  methods  which  may  be  advantageously  employed 
for  the  estimation  of  copper.  The  operations  of  the  dentist,  however, 
are  chiefly  confined  to  the  examination  of  amalgam  alloys.  The  alloy 
should  first  be  acted  upon  by  nitric  acid ;  silver,  if  present,  may  then  be 
recovered  in  the  form  of  chloride  ;  after  which  the  copper  may  be  pre- 
cipitated from  the  remaining  solution  either  as  oxide,  sulphide,  or  in  the 

^  Fletcher. 


138  METALS  AND  ALLOYS. 

metallic  state.  When  attempting  the  estimation  of  an  alloy  a  qualitative 
examination  should  first  be  made,  and  if  the  solution  to  be  examined 
is  found  to  contain  no  other  metal  whose  oxide  is  thrown  down  by 
caustic  potassa,  an  excess  of  that  agent  is  to  be  added.  In  the  resulting 
precipitate,  when  boiled,  washed,  dried,  and  weighed,  every  100  parts 
may  be  estimated  as  containing  79.85  per  cent,  of  metallic  copper. 

When  hydrogen  sulphide  or  ammonium  sulphide  is  employed  as  the 
reagent,  the  resulting  cupric  sulphide  is  usually  oxidized  by  nitric  acid, 
and  again  precipitated  by  potassa,  so  as  to  estimate  as  oxide. 

The  estimation  as  metallic  copper  is  accomplished  as  follows  :  Place 
in  the  solution  contained  in  a  platinum  dish  a  piece  of  zinc,  adding  also 
a  little  hydrochloric  acid.  The  electrolyzing  action  instantly  commences, 
and  continues  until  the  solution  is  colorless  and  the  zinc  completely  dis- 
solved. The  finely-divided  metallic  copper  will  be  found  at  the  bottom 
of  the  vessel.     This  is  to  be  well  washed,  dried,  and  weighed. 

Zinc. 
Atomic  weight,  65.2.     Symbol,  Zn. 

The  ancients  were  undoubtedly  acquainted  with  an  ore  (probably 
cadmia"^)  which  they  employed  with  copper  to  form  brass.  Many 
objects  of  ancient  manufacture,  analyzed  at  different  times,  have  been 
found  to  contain  zinc.^  The  extraction  of  the  metal  itself,  however,  is 
probably  a  modern  discovery. 

Metallic  zinc  is  never  met  with  in  nature.  The  principal  ores  are 
the  red  oxide,  the  sulphide  of  zinc  (blende),  and  the  native  carbonate 
(calamine).  The  latter  is  the  most  valuable  of  the  zinc  ores,  and  is  pre- 
ferred for  the  extraction  of  the  metal.  It  is  first  roasted  to  expel  water 
and  carbonic  acid,  then  mixed  with  fragments  of  coke  or  charcoal,  and 
distilled  at  a  full  red  heat  in  an  earthen  retort.  Carbon  monoxide 
escapes,  while  the  reduced  metal  volatilizes  and  is  condensed  by  suitable 
means. 

Properties. — Zinc  is  a  brittle,  crystalline  metal,  with  a  density  vary- 
ing from  6.8  to  7.2.  Until  about  the  commencement  of  the  present 
century  the  valuable  property  possessed  by  this  metal,  of  becoming 
quite  malleable  between  248°  and  302°  F.,  was  not  known  ;  hence 
prior  to  that  discovery  it  was  but  little  used  in  the  industrial  arts. 
Between  these  degrees  of  heat  it  may  be  rolled  or  hammered  without 
the  least  danger  of  fracture.  Sheet  zinc  of  commerce  is  manufactured 
by  this  means,  and  it  retains  its  malleability  when  cold.  Zinc  fuses  at 
773°  F.  (below  red  heat).  At  a  bright-red  heat  it  boils  and  volatilizes^ 
and  if  heated  in  air  combustion  takes  place,  during  which  it  unites  with 
the  atmospheric  oxygen  with  brilliant  incandescence.  At  410°  F.  zinc 
is  so  brittle  that  it  may  be  powdered  in  a  mortar. 

Alloys. — With  mercury,  zinc  forms  an  exceedingly  brittle  amalgam. 
The  two  combine  in  the  cold  state,  but  union  is  greatly  facilitated  by 
heating.  Zinc  is  occasionally  employed  as  a  constituent  in  dental  alloys. 
An  amalgam  has  been    suggested,  the  proportions  of  which  are  "ap- 

^  An  ore  used  by  the  ancients  containing  cadmium  and  zinc 

'^  Phillips  made  a  number  of  analyses  of  such  objects,  all  of  which  showed  the 
presence  of  zinc. 


ZING.  139 

proximately  "  given  as — tin^  50  odd  ;  silver,  30  ;  gold,  5  to  7  ;  zinc,  2  to 
4  ;  and  recent  experiments  with  it  have  proved  so  satisfactory  that  it  has 
to  a  certain  extent  taken  the  place  of  platinum  in  dental  amalgams. 

Added  to  silver  in  the  proportion  of  2  of  zinc  to  1  of  silver,  a  nearly 
white  malleable  alloy  results. 

The  color  of  gold  is  heightened  by  the  addition  of  zinc,  while  its 
malleability  is  greatly  impaired.  Makins  state  that  gold  rendered  stand- 
ard by  zinc  is  a  greenish-yellow,  brittle  alloy,  with  a  specific  gravity 
above  the  mean. 

Combination  between  zinc  and  platinum  or  palladium  may  be  effected 
at  a  comparatively  low  temperature,  and  it  is  accompanied  by  evolution 
of  light  and  heat.  It  is  stated  that  an  alloy  of  1 6  parts  of  copper,  7  of 
platinum,  and  1  of  zinc  closely  resembles  16-carat  gold,  is  quite  malle- 
able, does  not  tarnish  in  air,  and  is  capable  of  resisting  cold  nitric  acid. 

Zinc  and  lead  mix  with  each  other  to  a  very  limited  extent.  If 
equal  parts  of  the  two  metals  are  melted  together  and  allowed  to  cool, 
they  will  be  found  to  have  separated  into  two  layers,  the  upper,  and  con- 
sequently the  lighter,  one,  zinc,  retaining  1.2  per  cent,  of  the  lead,  while 
the  lower  layer  consists  of  lead  alloyed  with  1.6  per  cent,  of  zinc.  The 
necessity  of  carefully  keeping  these  two  metals  separate  in  all  moulding 
operations  in  the  dental  laboratory  will  readily  be  appreciated,  as  a 
failure  to  observe  precaution  in  this  direction  will  be  followed  by  vex- 
atious consequences.  If  by  accident  lead  becomes  mixed  with  the  zinc 
.  used  for  dies,  the  lead,  by  its  greater  specific  gravity,  will  settle  to  the 
bottom  and  fill  up  the  deeper  portions  of  the  sand  matrix  representing 
the  alveolar  ridge,  the  most  prominent  part  of  the  die.  This  may  not 
be  discovered  until  an  attempt  to  swage  is  made,  when  the  die  will  be 
found  to  be  totally  unfit  for  the  purpose.  In  such  cases  the  mixed  metal 
should  be  discarded  and  new  zinc  substituted. 

Zinc  and  tin  unite  in  all  proportions  without  diflficulty.  Alloys  of 
zinc  and  tin  are  frequently  employed  in  casting  dies  for  swaging  plates. 
Richardson  ^  gives  a  formula  for  an  alloy  consisting  of  zinc  4  parts,  tin 
1  part,  which,  he  states,  fuses  at  a  lower  temperature,  contracts  less  in 
cooling,  and  has  less  surface  hardness  than  zinc.  Fletcher,  however, 
states  that  all  alloys  of  zinc  and  tin  are  superior  to  zinc  alone  for  dies. 
The  impression  from  the  sand  he  believes  to  be  much  finer,  and  the 
shrinkage  in  cooling  greatly  reduced.  Zinc  2,  tin  1,  is  given  as  the  best 
proportion.^  Makins  states  that  zinc  and  tin,  when  combined  in  equal 
proportions,  form  a  white,  hard  alloy,  not  very  malleable  or  ductile^ 
which  is  capable  of  being  worked  as  readily  as  brass. 

Zinc  and  copper  unite  in  various  proportions  to  form  many  different 
grades  of  brass,  kno\vn  respectively  as  pinchbeck,  Manheim  gold, 
similor,  Bath  metal,  Prince  Rupert's  metal,  Muntz's  sterro,  Gedge's  and 
Aich's  metals.  German  silver  and  Chinese  alloys  known  as  pakfong  and 
tutenag  are  also  alloys  of  zinc  and  copper,  with  the  addition  of  nickel. 

Dies  and  Counter-dies. — Zinc  is  the  metal  most  commonly  employed 
in  the  formation  of  dies  for  swaging  plates,  and  is  superior  to  any  of  its 
alloys.^     Another  important  application  of  zinc  is  in  the  formation  of 

'  Mechanical  Dentvitry.  ^  Practical  Dental  Metallurgy,  p.  69. 

*  The  author  has  not  found  the  alloys  of  zinc  and  tin  to  be,  in  any  respect,  superior  to 
zinc  alone  for  dies. 


140  METALS  AND  ALLOYS. 

counter-dies.  The  die  is  placed  in  the  iron  ring  when  a  Bailey  flask  is 
employed,  or  invested  in  the  moulding  sand  and  then  surrounded  by  a 
suitable  iron  ring  in  the  old-fashioned  way.  The  zinc  is  then  heated  and 
poured  in  upon  the  zinc  die  just  at  the  moment  of  complete  fusion. 
Should  the  metal  be  accidentally  allowed  to  remain  on  the  fire  too  long, 
and  thus  reach  a  higher  temperature  than  is  necessary,  it  should  not  be 
poured  until  it  begins  to  solidify  at  the  edges.  The  belief  seems  to 
be  pretty  general  that  melted  zinc  cannot  be  poured  upon  a  zinc  die 
without  causing  cohesion  ;  ^  but  if  the  necessary  precaution  regarding  the 
proper  temperature  at  which  the  metal  is  poured  is  observed,  it  is  im- 
possible for  union  to  take  place,  and  when  cool  the  die  and  counter-die 
will  separate  quite  as  readily  as  though  the  latter  was  of  lead.  It  fre- 
quently occurs  that  the  zinc  die  and  lead  counter-die  are  totally  inad- 
equate to  bring  a  plate  (particularly  if  the  latter  is  of  platinum-gold  or 
iridium-platinum)  into  perfect  adaptation  to  all  parts  of  a  model,  espe- 
cially where  the  palatal  arch  is  very  deep  and  the  rugse  are  prominent. 

The  zinc  counter-die  is  also  of  especial  service  in  partial  cases  where 
a  number  of  teeth  remain.  These  are  cut  off  from  the  plaster  model 
previous  to  moulding  within  one-sixteenth  of  an  inch  of  the  margin  of 
the  gum,  so  that  a  sufficiently  distinct  impress  may  be  made  in  the  plate 
to  serve  as  a  guide  in  filing  the  latter  to  fit  around  the  natural  teeth. 

Where  the  swaging  is  likely  to  be  attended  with  difficulty,  at  least 
three  sets  of  dies  and  counter-dies  should  be  made.  The  most  imperfect 
of  these  should  be  furnished  with  a  lead  counter-die,  and  used  as  a  pre- 
liminary die  upon  which  to  start  the  plate.  The  next  in  quality  may  be 
used  with  the  zinc  counter-die,  and  the  nearest  perfect  of  the  three,  with 
a  lead  counter,  reserved  as  a  finishing  die.  When  the  plate,  by  means 
of  the  horn  or  wooden  mallet  and  some  preliminary  swaging  with  a  light 
hammer,  has  been  made  to  assume  somewhat  the  form  of  the  die,  and 
has  been  carefully  carried  past  the  stage  when  pleating  or  wrinkling  of 
the  plate  is  likely  to  occur,  it  should  be  trimmed  to  the  proper  dimen- 
sions, annealed,  and  placed  between  the  die  and  zinc  counter-die,  and  at 
first  gently  tapped  with  a  hammer  until  the  die  passes  well  into  the 
counter-die,  when  one  or  two  sharp  blows  with  a  heavy  hammer,  either 
upon  the  die  or  its  counter,  will  carry  the  plate  into  perfect  adaptation 
to  all  parts  of  the  former.  Some  slight  compression,  however,  of  the 
prominent  points  of  the  die  is  likely  to  occur  in  the  use  of  the  zinc 
counter,  so  that  it  will  be  necessary  to  anneal  and  give  the  plate  two  or 
three  sharp  blows  between  the  finishing  die  and  its  lead  counter-die ; 
after  which  it  will  be  found  to  perfectly  fit  the  mouth  without  any 
attempt  to  compensate  for  contraction  of  the  zinc.^  It  will  be  seen  that 
the  zinc  counter-die  is  not  intended  to  supersede,  but  is  merely  used  as 
an  adjunct  to,  the  lead  counter,  and  there  is  probably  no  better  means  of 
carrying  the  plate  to  the  deep  parts  of  the  model  and  of  obtaining  a 
sharp,  well-defined  impress  of  the  rugse  and  prominent  parts  of  the 
model. 

^  If  the  melted  metal  be  poured,  at  a  temperature  of  800°  F.,  upon  a  die  having  a 
temperature  of  70°  F.,  the  fused  zinc  by  contact  with  the  iron  ring  and  by  radiation  will 
lose  heat  enough  to  cause  its  temperature  to  fall  far  below  the  fusing-point,  and  it  will 
probably  not  impart  to  the  die  more  than  400°  F. 

^  The  subject  of  shrinkage  of  zinc  when  used  for  dies  in  forming  metallic  plates  has 
been  fully  referred  to  on  pp.  77  and  78. 


ALUMINUM.  141 

Compounds  of  Zinc. — The  oxide  and  the  chloride  are  the  com- 
pounds of  this  metal  most  frequently  employed  by  dentists.  The  first 
forms  the  chief  ingredient  in  the  plastic  filling  materials  known  as  oxy- 
chlorides  and  oxyphosphates.  Zinc  oxide  is  a  white  powder,  the  product 
of  the  combustion  of  the  metal.  It  turns  yellow  on  heating,  but  resumes 
its  pure  white  color  on  cooling. 

Chloride  of  zinc,  prepared  by  acting  upon  the  metal  with  hydro- 
chloric acid  or  by  heating  metallic  zinc  in  chlorine,  is  a  fusible  deliques- 
cent substance  quite  soluble  in  water  and  alcohol. 

Oxychloride  of  zinc,  the  well-known  filling  material,  consists  of  a 
powder  and  a  fluid.  The  first  is  prepared  by  various  formulae.  One  in 
common  use  is  as  follows :  Grind  together,  in  a  mortar,  borax  2  grains, 
fine  silex  1  grain,  oxide  of  zinc  30  grains.  When  thoroughly  mixed 
these  are  placed  together  in  a  small  crucible  and  heated  to  bright  red- 
ness. This  is  called  the  frit,  and  when  cool  requires  grinding  to  again 
reduce  it  to  a  pulverulent  state.  It  is  then  thoroughly  mixed  with  three 
times  its  weight  of  calcined  oxide  of  zinc.  The  fluid  usually  employed 
with  the  powder  consists  of  chloride  of  zinc  diluted  with  water  in  the 
following  proportions  :  Deliquesced  chloride  of  zinc,  1  ounce  ;  water,  5 
or  6  drachms.  The  oxyphosphate  powders  are  similar  mixtures.'  The 
fluid,  however,  is  prepared  by  dissolving  in  pure  water  some  glacial 
phosphoric  acid,  and  then  evaporating  until  the  solution  attains  the  con- 
sistence of  glycerin. 

The  presence  of  zinc  in  solution  is  distinguished  by  the  following 
reactions  :  a  white  precipitate  soluble  in  excess  of  the  alkali  is  obtained 
by  the  addition  of  caustic  potash,  soda,  or  ammonia,  and  zinc  is  distin- 
guished from  all  other  metals  by  ammonium  sulphide,  which  precipitates 
white  sulphide  of  zinc,  insoluble  in  caustic  alkalies. 

Aluminum. 
Atomic  weight,  27.4.     Symbol,  Al. 

Occurrence. — Aluminum  is  never  found  in  the  metallic  state.  Of 
all  the  metals,  the  sources  of  alumina  are  the  most  numerous  and  abun- 
dant. Its  chief  combinations  are  with  silicon  and  other  bases.  These 
substances,  undergoing  atmospheric  changes,  form  clays  and  soils,  which 
under  the  influence  of  heat  and  moisture  become  fruitful.  It  would 
seem  that  its  presence  is  not  necessary  to  the  maintenance  of  animal  or 
vegetable  life,  since  no  traces  of  it  have  been  found  in  either.  Some  of 
the  compounds  of  aluminum  are  quite  unattractive,  but  there  are  a 
number  possessing  great  hardness  and  extraordinary  beauty.  The  fol- 
lowing, with  their  formulae,  are  a  few  examples  of  the  latter  : 

Ruby^ AlA- 

Sapphire AI2O3. 

Garnet (CaMgFeMn)3Al2Si30,2. 

Cyanite AljSiOs. 

^  Oxide  of  zinc  200  parts,  silex  8,  borax  4,  ground  glass  5,  levigated  under  water  to 
ensure  complete  admixture,  then  dried  by  evaporation,  calcined  at  a  white  heat,  and  pul- 
verized, have  been  found  to  be  equal  in  durability  and  working  qualities  to  any  of  the 
numerous  oxyphosphates  now  in  the  market. 

■''  Corundum,  the  ruby,  and  the  sapphire  have  the  same  chemical  formula,  Al^Oj. 


142  METALS  AND   ALLOYS. 

As  early  as  1760,  Guyton  de  Morveau  called  the  substance  obtained 
by  calcining  alum  alumina.  Lavoisier,  sixteen  years  later,  suggested 
the  existence  of  metallic  bases  of  the  earths  and  alkalies,  and  alumina 
was  thought  to  be  an  oxide  of  a  metal  which  was  called  aluminium ;  and 
thus  it  was  named  long  before  it  was  isolated. 

In  1807,  Sir  Humphrey  Davy  tried  to  decompose  alumina  by  means 
of  an  electric  current,  and  again  to  reduce  the  metal  by  vapor  of  potas- 
sium, in  both  of  which  experiments  he  failed. 

In  1827,  Wohler  isolated  the  metal  by  decomposing  aluminium 
chloride  by  potassium.  The  metal  first  isolated  by  Wohler  was  a  gray 
powder,  taking  under  the  burnisher  the  appearance  of  a  highly  polished 
metal.  Later,  in  1845,  Wohler  obtained  the  metal  in  small  malleable 
globules  by  making  a  vapor  of  aluminum  pass  over  potassium  placed  in 
platinum  vessels,  and  from  these  specimens  he  was  able  to  determine  the 
properties  of  the  metal  with  some  degree  of  accuracy. 

The  credit  of  the  reduction  of  aluminum  in  a  state  of  purity  and  the 
determination  of  its  true  properties  belong  to  H.  St.  Clair  Deville,  who 
in  1854  brought  it  from  the  rank  of  a  mere  laboratory  curiosity  to  that 
of  the  useful  metals. 

In  1854  the  emperor  Napoleon  III.,  in  the  hope  that  aluminum 
might  be  used  in  the  construction  of  armor  and  helmets  for  the  French 
cuirassiers,  authorized  experiments  on  a  large  scale  to  be  carried  on  at 
his  own  expense.  In  1855  the  emperor  put  the  necessary  funds  at  the 
disposal  of  Deville,  whose  experiments  were  continued  for  four  months, 
the  result  being  that  in  August  of  the  same  year  aluminum  was  placed 
on  the  market  in  Paris  at  300  francs  a  kilo. 

The  first  article  known  to  have  been  made  of  aluminum  was  a  baby- 
rattle  for  the  infant  prince  imperial,  for  which  purpose  it  was  well  fitted 
on  account  of  its  sonorousness ;  but  application  of  the  metal  to  the 
manufacture  of  cuirasses  and  helmets  was  decided  to  be  impracticable, 
and  the  idea  was  abandoned. 

Reduction  of  Aluminum. — A  mixture  of  the  double  chloride  of 
aluminum  and  sodium  or  the  double  fluoride  of  aluminum  and  sodium 
(cryolite)  is  heated  to  redness  with  the  metal  sodium,  when  energetic 
chemical  action  takes  place,  during  which  chloride  of  sodium  is  formed 
and  the  metal  aluminum  separated. 

Aluminum  may  be  separated  by  electrolysis.  The  electric  current 
from  a  ten-cell-battery,  provided  with  carbon  poles,  is  passed  through 
the  fused  salt.  The  metal  appears  at  the  negative  pole  in  large  glob- 
ules. 

In  1882  the  cost  of  aluminum  was  materially  lessened  by  inventions 
of  Webster  of  Birmingham,  England.  This  inventor's  method  of  pro- 
ducing the  rtietal  consisted  in  reducing  sodium  compounds  in  cast-iron 
pots  from  a  fused  bath  of  caustic  soda.  By  this  means  the  yield  of 
sodium  is  much  greater  than  by  the  method  of  Deville,  while  the  tem- 
perature required  in  the  operation  is  considerably  less. 

In  1859,  Mr.  Charles  M.  Hall  of  Ohio  obtained  letters-patent  for  an 
electrolytic  method  which  is  superior  to  any  that  preceded  it.  The  prin- 
cipal feature  of  this  process  is  the  electric  decomposition  of  alumina 
suspended  or  dissolved  in  a  fused  bath  of  the  salts  of  aluminum,  the 
current  reducing  the  alumina  without  affecting  its  solvent.     Mr.  Hall 


ALUMINUM.  143 

has  succeeded  in  producing  the  metal  aluminum  as  an  article  of  com- 
merce at  $2  per  pound. 

Aluminum  is  nearly  the  color  of  new  zinc.  It  is  very  malleable  and 
ductile,  and  admits  of  rolling  into  thin  sheets  or  it  may  be  drawn  into 
fine  wire.  It  is  highly  sonorous,  and  has  the  power  of  conducting  heat 
and  electricity  in  about  the  same  degree  as  silver.  It  is  only  two  and  a 
half  times  heavier  than  water  (four  times  lighter  than  silver).  Its 
specific  gravity  is  2.46,  and  it  melts  at  a  red  heat. 

Aluminum  does  not  oxidize  in  air,  and  is  not  attacked  by  sulphur 
•compounds.  It  is  not  attacked  by  strong  nitric  acid,  and  is  insoluble  in 
dilute  sulphuric  acid,  but  it  may  be  readily  dissolved  in  either  dilute  or 
strong  hydrochloric  acid,  which  is  its  true  solvent.  The  metal  is  easily 
dissolved  in  solutions  of  caustic  potash  or  soda. 

As  the  result  of  the  invention  of  tlie  electrical  furnace  of  the  Messrs. 
Cowles  of  Cleveland,  Ohio,  aluminum  bronze  is  made  directly  from 
corundum  (Al^Og).  Twenty-five  pounds  of  the  crushed  ore  is  mixed 
with  about  50  pounds  of  copper  and  12  pounds  of  a  mixture  of  charcoal 
and  electric-light  carbon,  and  placed  in  a  rectangular  box  of  firebrick 
lined  with  limed  charcoal  to  prevent  loss  of  heat  by  radiation  and  to 
protect  the  firebrick  from  disintegration.  The  charge  is  surrounded  on 
all  sides  by  a  layer  of  charcoal  to  prevent  the  alloy  from  being  contam- 
inated with  calcium  from  reduction  of  the  lime  present.  The  cast-iron 
slab  forming  the  cover  of  the  furnace  is  then  securely  luted  on,  and  the 
current  from  a  powerful  dynamo-electric  machine  is  passed  into  the  fur- 
nace by  means  of  two  large  electric-light  carbons  which  pass  through 
the  ends  of  the  furnace  and  into  its  contents.  It  requires  about  five 
hours  of  exposure  to  the  intense  heat  afforded  by  the  electric  current  to 
reduce  the  aluminum  from  its  ore.  When  the  furnace  has  cooled  suf- 
ficiently the  product  of  the  reduction  will  be  found  to  consist  of  about 
50  pounds  of  a  copper  alloy  containing  from  15  to  35  per  cent,  of  alu- 
minum, which  may  be  brought  to  the  usual  10  per  cent,  standard  of 
aluminum  bronze  by  remelting  it  with  the  proper  proportion  of  copper. 

The  reaction  which  takes  place  in  the  process,  which  is  aided  by  the 
intense  heat  of  the  electric  current,  is  probably  as  follows  :  The  carbon 
unites  with  the  oxygen  from  the  corundum,  forming  carbon  monoxide  ; 
a  small  percentage  of  the  aluminum  remains  free,  mixed  in  small  par- 
ticles with  the  charcoal,  while  the  greater  portion  unites  with  the  copper 
to  form  the  alloy.  Nearly  all  the  oxide  is  reduced  and  the  charcoal  is 
changed  to  graphite.  Some  of  the  aluminum  unites  with  carbon  to  form 
the  carbide  of  aluminum.  The  fusing-point  of  10  per  cent,  aluminum 
bronze  is  somewhat  below  that  of  pure  gold. 

Aluminum  may  be  melted  in  an  ordinary  clay  crucible.  No  flux 
need  be  used.  Borax  is  not  only  useless,  but  is  actually  hurtful,  as 
aluminum  readily  attacks  the  glasses.  Biederman  ^  recommends  dipping 
the  scraps  which  are  to  be  melted  together  in  benzine  before  putting  in 
the  crucible.  Should  any  of  them  be  contaminated  with  solder,  it  may 
be  removed  by  immersing  in  nitric  acid,  which  does  not  act  upon  the 
aluminum. 

Annealing. — Aluminum  may  be  softened  by  heating  to  redness  and 
■chilling  suddenly  by  dropping  into  water.     Richards  recommends  rub- 

'  Aluminum :  its  Properties,  Metallurgy,  and  Alloys,  Richards. 


144  METALS  AND  ALLOYS. 

bing  the  piece  to  be  annealed  with  tallow  and  then  heating  until  the  fat 
is  carbonized,  when  at  the  moment  the  last  trace  of  black  disappears 
from  the  metal  it  may  be  dropped  into  water. 

Alloys. — Aluminum  forms  alloys  with  nearly  all  the  metals.  That 
with  copper  ^  is  the  most  important,  and  presents  a  closer  resemblance 
to  gold  than,  perhaps,  any  other  alloy.  It  is  used  for  articles  of  jewelry, 
for  mountings  of  astronomical  instruments,  and  for  making  balance- 
beams. 

German  dentists  are  now  using  aluminum  bronze  as  a  base  for  arti- 
ficial dentures.  Professor  Sauer,  in  a  paper  on  the  application  of  this 
alloy  to  dental  purposes,  says  "that  in  the  proportion  of  Cu  900  to 
Al  100  it  oxidizes  but  superficially  in  the  mouth,  and  is  as  strong  and 
resistant  to  attrition  as  1 8-carat  gold  ;  it  may  be  swaged  as  easily  as  20- 
carat  gold,  but  it  must  be  annealed  frequently,  and  it  is  necessary  to 
carry  the  heating  almost  to  whiteness,  for  if  the  bronze  be  merely  heated 
until  it  assumes  a  dark-red  color  it  remains  as  hard  as  before."  He 
also  gives  the  point  of  fusion  of  the  alloy  as  above  that  of  1 8-carat 
gold,  so  that  14-  or  1 8-carat  gold  solder  alloyed  with  copper  may  be 
used  upon  it  without  difficulty.  Although  the  alloy  is  highly  recom- 
mended by  many  German  dentists,  the  author  does  not  hesitate  to 
express  the  opinion  that  it  will  not  find  favor  in  this  country. 

The  following  solders  are  well  adapted  to  aluminum  bronze  : 

1.  Hard  Solder  for  10  -per  cent.  Aluminum  Bronze. 

Gold 88.88  per  cent. 

Silver 4.68       " 

Copper , 6.44       " 

100.00  per  cent. 

2.  Medium  Hard  Solder  for  10  per  cent.  Aluminum  Bronze. 

Gold 55.00  per  cent. 

Silver   .    , 27.00         " 

Copper 18.00        " 

100.00  per  cent. 

S.  Soft  Solder  for  Aluminum  Bronze. 

Copper,  70  per  cent.  \  -p  i  ^  oa  ^ 

Tin         30       "         j  ^^^^^ 14.30  per  cent. 

Gold 14.30 

Silver 57.10        " 

Copper 14.30 

100.00  per  cent. 

Aluminum  with  tin  and  zinc  forms  a  brittle  alloy,  and  with  silver  it 
yields  a  hard  though  workable  compound.  Aluminum  amalgamates 
with  mercury  by  the  assistance  of  heat,  and  at  the  boiling-jDoint  of 
mercury  the  solution  is  very  rapid. 

Aluminum  may  be  made  to  unite  with  mercury  by  the  intervention 
of  a  solution  of  caustic  potash  or  soda  If  the  surface  of  the  metal  be 
well  cleaned  or  moistened  with  the  alkaline  solution,  it  is  immediately 
melted  by  the  mercury ;  but  the  affinity  of  the  aluminum  for  oxygen  is 
greatly  increased  by  the  state  of  fine  division,  so  that  the  amalgam  when 
'  Aluminum  bronze — alloy  of  copper  with  5  per  cent,  of  aluminum. 


ALUMINUM.  145 

exposed  to  the  air  soon  becomes  covered  with  a  white  excrescence,  which 
Watts  found  to  be  pure  alumina. 

Aluminum  is  employed  in  the  manufacture  of  very  small  weights,  such 
as  the  milligramme  of  the  metric  system — a  use  to  which,  in  consequence 
of  its  exceedingly  low  specific  gravity,  it  is  particularly  well  adapted. 

Its  lightness,  strength,  and  resistance  to  oxygen  and  the  sulphur  com- 
pounds are  proj)erties  which  would  seem  to  point  to  this  metal  as  a  suit- 
able substance  as  a  base  for  artificial  teeth.  The  readiness,  however, 
with  which  it  is  attacked  by  alkaline  solutions  renders  it  unfit  for  use 
in  the  construction  of  a  permanent  artificial  denture. 

Aluminum,  notwithstanding  its  extreme  lightness,  may  be  cast  with 
great  exactness.  The  late  Dr.  J.  B.  Bean,  who  patented  a  process  for 
casting  aluminum,  succeeded  in  producing  castings  of  exquisite  fineness. 
Indeed,  it  may  be  stated  that  Bean  succeeded  in  overcoming  all  the 
physical  difficulties  encountered  in  the  effi:)rt  to  render  aluminum  avail- 
able in  prosthetic  dentistry,  but  its  susceptibility  to  the  action  of  alkaline 
solutions  finally  compelled  him  to  abandon  it. 

Dr.  C.  C.  Carroll  of  Meadville,  Pa.,  has  devised  a  means  of  casting  alu- 
minum which,  while  much  simpler  than  the  method  of  Dr.  Bean,  aifords 
results  equally  good.  The  metal  is  melted  in  a  plumbago  crucible  (see  p. 
476)  having  the  form  of  a  thick- walled  cylinder  closed  at  one  end,  which 
serves  as  a  bottom.  A  channel  is  formed  within  the  wall  of  the  crucible, 
one  orifice  of  which  terminates  within  at  the  side  close  to  the  bottom. 
Starting  from  the  orifice,  the  channel  rises  in  the  crucible  wall  near  the 
top,  making  a  sharp  return  upon  itself,  and  descends  in  a  parallel  course 
after  the  manner  of  a  siphon,  and  makes  its  exit  at  the  base  and  near 
the  side  of  the  crucible.  Here  it  terminates  in  an  iron  nipple  that  fits 
into  a  corresponding  socket  in  the  gateway  of  the  moulding-flask.  A 
cylindrical  plug  of  soapstone  which  fits  the  open  mouth  of  the  crucible 
is  provided  with  a  central  tube  of  brass,  to  the  free  end  of  which  is  con- 
nected by  a  short  length  of  rubber  tubing  a  large  rubber  bulb.  When 
the  metal  has  been  brought  to  a  state  of  fusion  the  crucible  is  connected 
by  means  of  the  iron  nipple  at  its  base  with  the  gateway  of  the  flask, 
which  has  been  previously  heated  to  redness,  and  the  soapstone  plug  is 
inserted  in  the  mouth  of  the  crucible.  Compression  of  the  air  at  this 
point  by  means  of  the  rubber  bulb  forces  the  fluid  metal  out  of  the 
crucible  through  the  syphon-like  channel  into  the  mould,  filling  the  most 
minute  lines  and  aifording  an  exceedingly  fine  casting.  Carroll  makes 
the  somewhat  extraordinary  statement  that  he  has  found  a  means  of 
controlling  the  contraction  of  the  metal,  together  with  its  tendency  to 
disintegrate  from  exposure  to  the  fluids  ^  of  the  mouth,  by  the  admixture 
of  other  metals.  Richards,  in  his  valuable  work  on  aluminum,  states 
that  to  overcome  the  difficulties  of  contraction  and  corrosion  by  the 
fluids  of  the  mouth  Dr.  Carroll  adds  "  a  little  copper,  which,  he  says, 
decreases  the  contraction,  while  the  addition  of  some  platinum  and  gold 
renders  it  unalterable  in  the  mouth." 

Aluminum  may  be  cast  upon  plain  teeth  with  comparative  safety, 
provided  the  metal  is  prevented  from  overlapping  the  necks  of  the  teeth. 
But  when  gum-teeth  are  employed,  either  single  or  in  sections,  their 
fracture  is  almost  certain  to  follow  the  contraction  incident  to  the  cooling 

^  Demonstration  before  dental  class  University  of  Pennsylvania. 
10 


146  METALS  AND  ALLOYS. 

of  the  metal.  Specimens  of  Dr.  Carroll's  work  have  fully  jDroved  this, 
and  it  was  the  one  difficulty  which  finally  defeated  Dr.  Bean's  eiforts  by 
compelling  him  to  cast  his  plate  separate  from  the  teeth  ;  for,  if  it  had 
been  practicable  to  cast  the  metal  directly  upon  block-teeth  without 
danger  of  fracture,  the  denture  would  have  lasted  for  at  least  six  or  eight 
years ;  but  the  necessity  of  attaching  the  teeth  to  the  plate  by  another 
metal  so  hastened  disintegration  that  a  few  months  only  were  necessary 
to  render  the  piece  useless. 

There  are  two  methods  which  have  been  employed  in  the  construc- 
tion of  artificial  dentures  of  this  metal.  The  one  most  frequently  re- 
sorted to  consists  in  merely  swaging  a  plate  in  the  ordinary  way.  A 
number  of  countersunk  holes  are  then  made  along  the  part  covering  the 
top  of  the  alveolar  ridge  as  a  means  of  fastening  the  teeth,  which  are 
attached  with  rubber  or  celluloid.  Sets  of  teeth  made  in  this  way  have 
been  known  to  do  good  service  for  eight  or  nine  years,  but  they  showed 
unmistakable  evidence  of  the  action  of  the  oral  fluid.  In  the  second 
method  the  plate  is  cast,  but  disintegration  in  this  case  progresses  with 
much  greater  rapidity.  As  the  plate  is  cast  separate  from  the  teeth,  and 
the  latter  are  afterward  attached  by  means  of  tin  or  an  alloy  of  tin  and 
aluminum,  it  is  probable  that  the  galvanic  action  incident  to  the  pres- 
ence of  the  two  metals  greatly  hastens  dissolution  of  the  plate. 

For  some  time  the  difficulty  of  soldering  aluminum  prevented  the 
metal  from  being  applied  to  useful  purposes.  The  solder  recommended 
for  general  use  in  the  manufacture  of  articles  of  ornamentation  is  com- 
posed of  copper,  4  parts  ;  aluminum,  6  parts  ;  zinc,  90  parts.  The  use 
of  this  requires  some  skill  and  experience.  At  the  moment  of  fusion 
small  aluminum  tools  are  used,  the  friction  of  which  is  necessary  to 
induce  adhesion.  Borax  cannot  be  employed  as  a  flux,  as  it  is  liable  to 
attack  the  metal  and  prevent  union. 

Another  method  of  uniting  two  pieces  of  aluminum  with  ordinary 
solder,  in  conjunction  with  silver  chloride  as  a  flux,  has  recently  been 
recommended  by  F.  J.  Page  and  H.  A.  Anderson  of  Waterbury,  Conn. 
The  finely  powdered  fused  silver  chloride  is  spread  along  the  lines  of 
junction,  and  the  solder  is  melted  with  a  blowpipe  or  other  device. 
The  union  thus  obtained  is  said  to  be   perfectly  strong  and  reliable.^ 

The  following  alloys  are  also  used  as  solders  in  unalloyed  aluminum 
articles  of  jewelry  : 

I.  II.  III.  IV. 

Zinc 80  85  88  92 

Aluminum 20  15  12  8 

In  soldering  with  these  alloys  a  mixture  is  used  as  a  flux  consisting 
of  3  parts  copaiba  balsam,  1  part  Venetian  turpentine,  and  a  few  drops 
of  lemon-juice.     The  soldering-iron  is  dipped  into  the  mixture. 

Mr.  Wm.  Frismuth  of  Philadelphia  recommends  the  following  solders 
for  aluminum,  with  vaselin  as  the  flux  : 

Soft  Solder. 

Pure  Block  Tin from  99  to  90  parts. 

Bismuth "       1  "  10     " 

^  Chemical  News,  iv.  81.  , 


ALUMINUM.  147 

Hard  Solder. 

Pure  Block  Tin from  98  to  90  parts. 

Bismuth "       1  "     5     " 

Aluminum "        1    "   5     '' 

Schlo-sser  ^  recommends  two  solders  containing  aluminum  as  espe- 
cially suitable  for  dental- laboratory  use  .* 

Platinum-aluminum  Solder. 

Gold 30  parts. 

Platinum 1     " 

Silver 20     " 

Aluminum 100     " 

Gold-aluminum  Solder. 

Gold 50  parts. 

Silver 10     " 

Copper 10     " 

Aluminum 20     " 

O.  M.  Thowless  has  patented  the  following  solder  for  aluminum  and 
method  of  applying  it  ; 

Tin 55  parts. 

Zinc 23     " 

Silver 5     " 

Aluminum 2     " 

The  silver  and  aluminum  are  first  melted  together ;  the  tin  and  zinc  are 
then  added  in  the  order  named.  The  surfaces  to  be  soldered  are  im- 
mersed in  dilute  caustic  alkali  or  a  cyanide  solution,  and  then  washed 
and  dried.  They  are  next  heated  over  a  spirit  lamp,  coated  with  the 
solder,  and  clamped  together ;  small  pieces  of  the  solder  being  placed  at 
the  points  of  union,  the  whole  is  then  heated  to  the  melting-point.  No 
flux  is  used. 

The  only  oxide  of  this  metal  is  alumina  (AljOg).  It  is  prepared  by 
mixing  a  solution  of  alum  with  excess  of  ammonia.  The  resulting  pre- 
cipitate (aluminum  hydrate)  is  of  a  bulky,  gelatinous  character,  and 
requires  to  be  calcined  at  a  high  temperature ;  after  which  it  may  be 
described  as  a  perfectly  white  powder,  soluble  in  caustic  potassa  or  soda, 
and  not  readily  acted  upon  by  acids. 

Corundum  and  emery  are  nearly  pure  alumina.  The  ruby  and 
sapphire  are  also  transparent  varieties  of  alumina  in  a  crystalline  state, 
their  brilliant  colors  being  due  to  oxide  of  chromium. 

The  only  knoAvn  sources  of  corundum  until  1869  were  a  few  rivers 
in  India,  where  it  occurred  in  crystals  having  the  form  of  the  double 
six-sided  cone.  Its  cost  at  that  time  was  from  twelve  to  twenty-five 
cents  a  pound.  Since  that  date,  however,  it  has  been  discovered  in 
inexhaustible  quantities  in  Georgia,  North  Carolina,  and  Pennsylvania. 
At  present  it  can  be  bought  at  the  mines  at  $10  per  ton. 

(For  the  discrimination  of  the  salts  of  aluminum  see  any  of  the 
recent  works  on  chemistry.) 

^  Richards. 


148  METALS  AND  ALLOYS. 

Tin. 
Atomic  weight,  118.     Symbol,  Sn  (Stannum). 

The  metal  tin  has  been  known  for  probably  three  thousand  years. 
It  is  found  in  all  parts  of  the  world,  chiefly  as  oxide.  In  reducing  the 
ore  it  is  first  powdered  and  roasted  to  free  it  of  sulphur  and  arsenic.  It 
is  then  exposed  to  a  high  temperature  with  charcoal,  and  the  metal  is 
thus  liberated. 

Pure  tin  is  white  in  color  and  is  perfectly  soft  and  malleable.  It  has 
a  density  of  7.3,  and  its  fusing-point  is  458.6°  F.  (237°  C).  It  is  but 
slightly  acted  upon  by  air,  but  when  heated  much  above  its  melting- 
point  it  oxidizes  freely,  and  is  converted  into  a  yellowish-white  powder — 
the  well-known  polishing  putty.  The  action  of  nitric  acid  upon  tin  is 
to  convert  it  into  a  white  hydrated  dioxide.  It  is  dissolved  by  hydro- 
chloric acid,  assisted  by  heat,  and  forms  stannous  chloride.  Nitro- 
hydrochloric  acid  acts  upon  tin  with  much  energy,  converting  it  into 
stannic  chloride. 

Alloys. — Tin  is  readily  dissolved  in  mercury.  With  silver  it 
forms  a  malleable  alloy,  which  is  considerably  harder  than  tin.  The  late 
Dr.  Bean  used  tin  alloyed  with  a  small  percentage  of  silver  for  lower  den- 
tures, which  he  cast  directly  upon  the  teeth  after  the  ordinary  cheoplastic 
method. 

Alloys  of  tin  and  silver,  in  which  the  former  is  slightly  in  excess,. 
are  much  used  as  amalgam  alloys.  Tin  10,  silver  8,  gold  1,  is  also  fre- 
quently employed  in  filling  teeth  ;  and  tin  10,  silver  8,  gold  1,  copper  1, 
has,  according  to  Fletcher,  been  largely  used  as  "  gold-and-platinum  "^ 
amalgam.  It  is  stated  that  from  5  to  7  per  cent,  of  copper  has  the 
property  of  replacing  platinum  in  amalgams,  conferring  the  quick- 
setting  quality  claimed  for  platinum.^ 

Dr.  G.  F.  Reese  has  formed  an  alloy  for  a  base  for  artificial  dentures 
composed  of  20  parts  of  tin,  1  of  gold,  and  2  of  silver.^  This  is  cast 
directly  upon  the  teeth,  the  process  being  similar  to  the  cheoplastic 
method. 

The  alloys  which  have  been  used  in  the  cheoplastic  process  are  chiefly 
composed  of  tin,  silver,  bismuth,  and,  in  some  instances,  cadmium  and 
antimony. 

According  to  Makins,  gold  and  tin  form  a  malleable  alloy,^  and  gold 
reduced  to  standard  by  pure  tin  retains  its  malleability.* 

Tin  and  platinum  in  equal  proportions  aiford  a  hard  and  quite  brittle 
alloy,  fusible  at  a  comparatively  low  temperature.  When  it  is  remem- 
bered that  the  fusing-points  of  these  metals  almost  represent  extremes  of 
temperature,  it  would  seem  that  their  union  must  be  attended  with  dif- 
ficulty, but,  as  has  already  been  stated,^  it  is  probable  that  some  affinity 
exists  between  the  two,  as  platinum  is  readily  dissolved  by  and  with  the' 
fused  tin. 

'  F.  Fletcher.         ^  Alloys  and  Amalgams  chemically  Considered,  J.  Morgan  Howe,  M.  D. 

^  A  precipitated  alloy  of  gold  and  tin,  having  the  form  of  a  black  powder,  may  be 
formed  by  acting  upon  a  concentrated  solution  of  trichloride  of  gold  with  stannous 
chloride. 

*  The  author  has  found  that  the  color  and  the  general  working  qualities  of  gold  are- 
greatly  impaired  by  admixture  with  small  quantities  of  tin. 

*  See  chapter  on  "  Alloys." 


TIN.  149 

With  palladium,  tin  is  said  to  form  a  brittle  alloy. 

With  lead,  tin  forms  the  chief  part  in  the  alloys  used  for  soft  solder- 
ing, and  in  the  compounds  known  as  pewter  and  britannia  metal.  Tin 
solders  are  composed  of  2  parts  of  tin  to  1  of  lead,  pewter  consists  of  4 
parts  of  tin  to  1  of  lead,  while  britannia  metal  is  formed  by  the  addition 
of  small  quantities  of  antimony  and  copper. 

Alloys  of  tin  and  lead  are  harder  and  tougher  than  either  metal 
singly,  and  they  are  more  fusible  than  the  mean  of  their  constituents. 
The  addition  of  bismuth  to  such  an  alloy  lowers  the  melting-point  to  a 
remarkable  degree,  and  the  fusing-point  is  still  further  reduced  by  the 
addition  of  cadmium.  Thus,  an  alloy  composed  of  15  parts  of  bismuth, 
8  of  lead,  4  of  tin,  and  3  of  cadmium  fuses  at  145°  F.  ( =  63°  C). 

Dr.  C.  M.  Richmond  uses  a  fusible  alloy  in  crown-  and  bridge-work 
which  he  states  is  as  hard  as  zinc,  and  can  be  melted  at  150°  F,,  and 
poured  into  a  plaster  impression  without  generating  steam.  The  formula 
of  this  alloy  is  as  follows  : 

Tin 20  parts  by  weight. 

Lead 19      " 

Cadmium 13      "  " 

Bismuth 48      "  " 

The  following  fusible-metal  alloys  are  also  suitable  for  the  purpose  ; 


Tin. 

Lead. 

Bismuth. 

Melting-point  of  alloy,  Fahr. 

1 

2 

2 

236° 

5 

3 

3 

202° 

3 

5 

8 

197° 

Dr.  George  W.  Mellott  of  Ithaca,  N.  Y.,  to  whom  is  due  the  credit 
of  having  introduced  the  use  of  fusible  metal  and  the  compound  called 
"  moldine  "  into  bridge- work,  uses  an  alloy  of — 

Tin : 5 

Lead 3 

Bismuth 8 

Moldine,  of  which  Mellott  forms  his  matrix  for  casting,  is  a  com- 
pound of  potter's  clay  and  glycerin. 

The  alloy  known  as  "  Wood's  metal,"  occasionally  employed  by  den- 
tists in  replacing  teeth  on  vulcanite  plates,  is  composed  of  7  j)arts  of 
bismuth,  6  of  lead,  and  1  of  cadmium,  and  fuses  at  180°  F.  (=  82°  C.) 
— a  temperature  much  below  the  boiling-point  of  water.  In  replacing  a 
broken  tooth  by  means  of  Wood's  metal  the  usual  dovetail  is  cut  in  the 
rubber  plate  with  a  fine  saw,  the  tooth  is  fitted  to  its  place,  and  the  fus- 
ible alloy  is  packed  in  with  a  spatula  heated  in  a  spirit-lamp. 

Lead  75,  tin  5,  and  antimony  20  parts  is  the  composition  of  the  best 
quality  of  type-metal. 

With  copper,  tin  affords  a  number  of  very  useful  alloys.  Bell  metal 
is  formed  of  78  parts  of  copper  to  2  of  tin.  Gun  metal  is  formed  of  90 
per  cent,  of  copper  to  10  per  cent,  of  tin.  Speculum  metal  is  formed  of 
6  parts  of  copper,  3  of  tin,  and  1  of  arsenic. 

Babbitt  metal,  named  after  Isaac  Babbitt  of  Boston,  Mass.,  is  an 
alloy  consisting  of  9  parts  of  tin,  10  parts  of  copper,  used  for  journal- 


150  METALS  AND  ALLOYS. 

boxes  {vide  patent  1839).  Many  modifications  have  since  been  made  in 
this  alloy,  but  the  term  is  still  applied  to  any  white  alloy  employed  in 
the  construction  of  bearings,  to  distinguish  it  from  the  ''  bronzes  "  and 
"  brasses." 

Mr.  Fletcher  recommends  an  alloy  of  copper  4  pounds,  Banca  tin 
96  pounds,  regulus  antimony  8  pounds.  This  alloy  is  said  to  be  nearly 
as  hard  as  zinc,  while  its  shrinkage  is  much  less.  These  qualities, 
together  with  the  low  temperature  at  which  it  fuses,  entitle  it  to  a  place 
in  the  dental  laboratory  for  the  preparation  of  dies  and  counter-dies. 

Dr.  L.  P.  Haskell  recommends  the  formula  tin  72.72,  copper  9.09, 
antimony  18.18. 

Bronze  is  an  alloy  of  copper  and  tin,  and  sometimes  zinc.  It  is 
affected  by  changes  of  temperature  in  a  manner  precisely  the  reverse  of 
that  in  which  steel  is  affected,  becoming  soft  and  malleable  when  quickly 
cooled,  and  hard  and  brittle  when  allowed  to  cool  slowly.  The  art  of 
making  bronze  was  practised  before  any  knowledge  of  the  working  of 
iron  existed,  and  it  was  used  at  a  very  early  period  in  the  manufacture 
of  weapons. 

Commercial  tin  is  liable  to  contain  minute  quantities  of  lead,  iron, 
copper,  arsenic,  antimony,  bismuth,  etc.  Pure  tin  may  be  precipitated 
in  crystals  by  the  feeble  galvanic  current  excited  by  immersing  a  plate 
of  tin  in  a  strong  solution  of  stannous  chloride.  Water  is  carefully 
poured  on,  so  as  not  to  disturb  the  layer  of  tin  solution.  The  pure 
metal  will  be  deposited  on  the  bar  of  tin  at  the  point  of  junction  of  the 
water  and  the  metallic  solution. 

Perfectly  pure  tin  may  also  be  obtained  by  dissolving  commercial  tin 
in  hydrochloric  acid,  by  which  it  is  converted  into  stannous  chloride. 
After  filtering,  this  solution  is  evaporated  to  a  small  bulk  and  treated 
with  nitric  acid,  which  instantly  converts  the  stannous  chloride  into 
stannous  oxide.  This  is  thoroughly  washed  and  dried,  and  exposed  to 
red  heat  in  a  crucible  with  charcoal.  A  button  of  pure  tin  will  be 
found  at  the  bottom  of  the  crucible. 

Pure  tin  in  the  form  of  foil  is  frequently  used  in  filling  teeth,  for 
which  purpose  it  doubtless  ranks  next  to  gold.  The  foil  is  also  em- 
ployed in  connection  with  non-cohesive  gold  in  filling  approximal  sur- 
faces of  cavities  in  bicuspids  and  molars.  Two  sheets  of  foil,  one  of 
gold  and  the  other  of  tin,  are  placed  together  and  made  into  mats  or 
cylinders.  These  are  carefully  packed  against  the  cervical  margins  of 
the  cavity.  The  frequent  failure  of  ordinary  gold  fillings  at  this  point 
has  led  some  practitioners  to  entertain  the  theory  that  between  the 
tooth-substance  and  the  gold  there  is  galvanic  action,  to  which  the 
lime  salts  of  the  tooth  yield,  and  that  by  the  combination  of  two  metals, 
whether  tin  and  gold  or  amalgam  and  gold,  the  galvanic  action  is  con- 
fined to  the  metals,  the  tooth-substance  being  thus  protected. 

The  appearance  of  a  filling  formed  of  tin  and  gold  would  seem  to 
confirm  this  theory,  as  it  soon  becomes  dark  in  color,  and  presents  a 
surface  resembling  amalgam,  but  it  effectually  protects  the  margins  from 
decay.- 

Tin,  having  but  slight  affinity  for  sulphur,  is  largely  used  in  the 

^  Prof.  James  Truman,  Report  of  Proceedings  of  Odontological  Society  of  Pennsylvania, 
November,  1881. 


TIN.  151 

formation  of  models  in  the  construction  of  vulcanite  dentures,  and  tin- 
foil forms  the  best  coating  for  plaster  casts  in  the  vulcanizing  process. 

The  manufacturers  of  miscellaneous  rubber  articles  do  not  use 
plaster  in  forming  the  matrix  in  which  the  rubber  is  packed  before 
vulcanizing,  having  long  since  discovered  that  contact  with  plaster 
lessens  the  toughness  and  elasticity  of  the  indurated  rubber :  they  there- 
fore form  every  matrix  of  sheet  tin,  which  is  placed  in  a  suitable  iron 
box  and  covered  tightly  with  dry  powdered  soapstone  (steatite). 

Dr.  J.  S.  Campbell,  wdio  introduced  the  vulcanizer  known  as  the 
''  New  Mode  Heater,"  described  a  means  whereby  all  parts  of  the 
matrix  contained  in  the  flask  in  constructing  rubber  dentures  could  be 
covered  by  sheet  tin,  so  that  after  vulcanizing  and  the  removal  of  the 
sheet  tin  or  foil  the  surface  of  the  rubber  would  be  found  to  be  smooth 
and  highly  polished,  and,  if  the  "  waxing  up  "  had  been  carefully  done, 
little  or  no  Bling  and  scraping  were  needed.  The  method  demonstrated 
by  Dr.  Campbell  possessed  precision  and  saved  labor,  and  it  is  to  be 
regretted  that  it  was  not  generally  adopted  by  mechanical  dentists,  who 
have  not  improved  to  any  extent  upon  the  slovenly  methods  employed 
in  1858,  when  indurated  rubber  was  first  employed  in  dental  practice. 

When  tin-foil  is  used  as  a  coating  for  plaster  casts  in  rubber  work, 
the  foil  may  be  removed  with  the  finger-nail  if  the  surface  of  the  plaster 
model  was  smooth  and  hard,  and  this  condition  of  the  plaster  surface  can 
be  obtained  by  using  nothing  as  a  coating  for  the  plaster  impression  but 
sandarac  varnish,  and  carefully  avoiding  the  use  of  oil  or  solutions  of 
soap  as  a  means  of  separating  the  impression  from  the  model.  If,  how- 
ever, in  consequence  of  the  roughened  surface  of  the  plaster  cast  the 
tin-foil  adheres  so  tenaciously  that  it  cannot  be  removed  except  by 
means  of  a  solvent,  hydrochloric  acid  is  the  only  one  that  will  accom- 
plish that  end  without  injury  to  the  rubber.  Both  nitric  and  nitro- 
hydrochloric  acids  should  be  avoided,  as  they  attack  indurated  rubber 
with  more  or  less  energy. 

Lower  vulcanite  dentures  may  be  loaded  with  tin  to  give  them  addi- 
tional weight,  and  by  lessening  the  quantity  of  rubber  prevent  the 
occurrence  of  porosity  during  the  process  of  vulcanizing. 

Solvents. — Tin  is  readily  dissolved  by  either  of  the  three  mineral 
acids.  Sulphuric  acid  converts  it  into  stannic  sulphate.  Tin  dissolved 
in  hydrochloric  acid  forms  stannous  chloride.  By  the  action  of  dilute 
nitric  acid  tin  is  not  dissolved,  but  is  converted  into  stannic  oxide,  which 
settles  to  the  bottom  of  the  vessel  as  a  white  powder.  This,  when  ren- 
dered anhydrous  by  heating  to  redness,  affords  the  well-known  polishing- 
powder  called  "  polishing  putty.'' 

Chlorides. — There  are  two  chlorides  of  tin — stannous  chloride  or 
protochloride  of  tin  (SnCla),  and  stannic  chloride  or  bichloride  of  tin 
(SnCl4).  Stannous  chloride  is  prepared  by  dissolving  tin  in  hydro- 
chloric acid,  the  action  being  assisted  by  gentle  heat.  Stannic  chloride 
is  obtained  by  dissolving  tin  in  nitro-hydrochloric  acid  (aqua  regia). 
These  two  compounds  of  tin  are  employed  in  the  preparation  of  purple 
of  Cassius,  in  which  process  stannous  chloride  is  added  to  a  mixture  of 
stannic  chloride  and  trichloride  of  gold  (see  page  109). 

(For  other  compounds  of  tin  see  works  on  chemistry.) 

Discrimination. — Tin  is  detected  before  the  blowpipe  by  fusing  the 


152  METALS  AND  ALLOYS. 

compound  under  examination  on  charcoal  with  sodium  carbonate,  when 
a  bead  of  the  metal  is  obtained.  From  a  tin  solution  caustic  potash  and 
soda  precipitate  a  white  hydrate,  soluble  in  excess.  Ammonia  affords  a 
similar  precipitate,  not  soluble  in  excess.  Hydrogen  sulphide  and 
ammonium  sulphide  throw  down  a  dark-brown  precipitate  of  mono- 
sulphide.  Trichloride  of  gold  added  to  a  dilute  solution  of  stannous 
chloride  causes  a  purple  precipitate  (purple  of  Cassius). 


CHAPTER   III. 

PRINCIPLES  OF  METAL  WORK. 

Sheet-metal  Work  in  Detail;  the  Manufacture  of  Taps, 
Screws,  Nuts,  Threaded  Wires,  Bands,  Regulating  Ap- 
pliances, ETC, — Special  Tools  and  Appliances  Required. 

By  C.  L.  Goddard,  A.  M.,  D.  D.  S. 


Plate  or  Sheet  Metal. 

As  the  refining,  alloying,  and  working  of  metals  and  forming  an  ingot 
have  been  described  in  other  parts  of  this  work,  the  present  chapter  will 
begin  at  that  point. 

The  Ingot. — After  an  ingot  of  metal  has  been  moulded  it  should  be 
forged  for  three  purposes — to  test  its  malleability,  to  reduce  its  thick- 
ness, and  to  bevel  one  edge  slightly. 

Sheet-metal  or  Plate. — Although  an  ingot  may  be  reduced  to  plate 
by  hammering,  it  is  a  slow  and  laborious  process.  It  is  better  to  use  a 
rolling-mill,  such  as  is  shown  on  page  37. 

The  mill  should  be  provided  with  long  handles,  and  both  ends  of  the 
rolls  should  be  adjustable  by  means  of  one  screw.  A  geared  mill  is  much 
easier  to  work  than  one  without  gearing. 

After  annealing,  the  bevelled  edge  of  the  ingot  should  be  introduced 
between  the  rollers,  which  should  be  adjusted  so  as  to  only  slightly  com- 
press it  as  the  handles  are  turned.  For  rolling  a  large,  thick  ingot  two 
persons  are  required,  one  for  each  handle.  The  rolls  should  be  brought 
nearer  together,  the  ingot  passed  through  again,  and  the  process  repeated, 
with  occasional  annealing,  till  it  is  reduced  to  plate  of  the  desired  thick- 
ness. If  plate  is  desired  wider  than  the  ingot,  it  should  be  rolled  till 
the  desired  width  is  obtained,  then  annealed,  reversed,  and  rolled  cross- 
ways  till  reduced  to  the  desired  thickness.  If,  in  rolling,  the  plate 
curves,  showing  that  one  edge  is  thinner  than  the  other,  screw  the  rollers 
nearer  together  on  the  thicker  side  of  the  plate  and  roll  again,  repeat- 
ing the  process  till  the  plate  is  reduced  evenly.  If  this  precaution  is 
neglected  and  the  plate  merely  reversed  and  rolled  again,  it  will  be 
rolled  thinner  on  the  edges  than  in  the  middle,  and  will  crumple. 

For  bands  for  regulating  appliances  plate  is  best  rolled  from  round 
wire.  This  gives  a  long,  narrow  ribbon,  the  edges  of  which  are  less  liable 
to  tear  than  the  edges  of  cut  plate. 

The  thickness  of  metal  plate  and  also  the  size  of  wire  are  measured 
with  a  plate  or  wire  gauge  (page  38).     There  are  several  of  these,  but 

153 


154  PRINCIPLES  OF  METAL   WORK. 

the  one  used  most  by  dentists  is  the  American  standard  wire  gauge,  called 
generally  the  Brown  &  Sharp  (or  B.  &  S.)  gauge.  All  numbers  of  plate 
and  wire  in  this  chapter  refer  to  this  gauge,  and  are  generally  marked 
B.  &  S.,  as  band  ribbon  No.  32  to  36  B.  &  S.  gauge,  or  wire  No.  16  or 
18  B.  &  S.  gauge,  etc. 

Matebials  for  Regulating  Appliances. 

Quite  a  variety  of  materials  are  needed  for  regulating  appliances,  for 
bands,  caps,  screws,  nuts,  springs,  clasps,  plates,  hoods,  etc. 

Materials  for  such  use  should  not  be  deleterious  to  the  teeth  in  any 
respect,  and  should  be  inconspicuous.  Some  should  be  soft  and  pliable, 
others  hard  and  rigid,  others  elastic.  They  should  not  corrode  nor  tarnish 
in  the  mouth.  It  is  not  always  possible  to  obtain  all  the  desirable  qual- 
ities in  one  material,  hence  it  is  sometimes  necessary  to  sacrifice  one 
quality  for  another  that  is  more  important.  Some  metals  or  alloys  that 
corrode  or  tarnish  readily  in  the  mouth  have  qualities  of  such  import- 
ance that  less  important  ones  must  be  ignored.  Utility  must  not  be  sac- 
rificed to  appearance. 

For  bands  the  most  suitable  metals  are  platinum,  combined  platinum 
and  gold,  and  German  silver.  Platinum  is  best,  because  it  does  not  cor- 
rode and  may  be  soldered  with  pure  gold  without  a  flux.  It  is  soft  and 
pliable,  and  may  be  easily  bent  around  a  tooth  and  burnished  accurately 
to  fit  the  contour.  To  some  patients  the  color  is  objectionable,  hence  for 
the  anterior  teeth  the  writer  prefers  a  combination  of  platinum  and  gold 
made  for  crown-work,  platinum  coated  with  gold  on  one  side.  This  has 
all  the  advantages  of  platinum  in  strength,  and  all  the  advantages  of  gold 
in  appearance.  It  may  be  soldered  with  20-carat  solder.  Coin  gold  or 
22-carat  is  also  good  for  bands,  but  must  be  used  thicker  than  platinum 
to  obtain  the  requisite  strength. 

German  silver  was  introduced  for  regulating  appliances  by  Dr.  E.  H. 
Angle.  It  is  strong,  elastic  when  rolled  without  annealing,  yet  very  soft 
and  pliable  when  annealed.  It  may  be  soldered  with  gold  or  silver 
solder.  It  has  the  disadvantage  of  discoloring  easily,  though  the  more 
highly  it  is  polished  the  less  it  discolors.  It  may  be  protected  by  electro- 
plating with  gold  or  nickel,  but,  unless  the  plating  is  quite  thick,  dis- 
coloration will  still  take  place. 

Vulcanite  is  used  as  in  prosthetic  work  for  making  plates  for 
attachment  of  ligatures,  rubber  bands,  springs,  etc.  It  has  been 
replaced  to  a  very  great  extent  by  appliances  attached  directly  to 
the  teeth. 

Tubes. — For  use  on  posterior  teeth  or  on  the  lingual  surface  of  ante- 
rior teeth  nothing  is  superior  to  German  silver.  For  use  on  the  anterior 
teeth  tubes  may  be  made  of  coin  or  22-carat  gold,  about  No.  30. 

Bars  may  be  made  of  German  silver  or  clasp  gold  according  to  the 
position  in  the  mouth,  and  soldered  with  gold  or  silver  solder. 

Wire  may  be  made  of  clasp  gold  or  German  silver.  Both  of  these 
materials  are  made  elastic  by  drawing  through  the  draw-plate,  but  an- 
nealing lessens  the  elasticity  of  the  former  and  entirely  removes  it  from 
the  latter.  The  former  retains  its  color  well  in  the  mouth,  while  the 
latter  discolors  very  easily. 


TOOLS  AND  APPLIANCES  NEEDED. 


155 


Piano  wire  is  more  useful  than  any  other  for  springs  for  moving 
teeth.  It  is  polished  steel,  and  possesses  more  elasticity  than  any  other 
wire  that  can  be  used  in  the  mouth,  yet  is  pliable  enough  to  be  readily 
bent  without  breaking.  In  some  mouths  it  oxidizes  so  rapidly  as  to 
materially  reduce  its  strength  in  a  few  days,  while  in  others  it  will 
merely  discolor  slightly,  but  still  retain  its  strength.  It  cannot  be 
hard  soldered  without  drawing  the  temper  so  much  as  to  ruin  its 
elasticity,  but  may  be  attached  to  other  metals  with  soft  solder  with- 
out injury. 

It  is  best  to  use  tubes  as  a  means  of  attachment,  so  that  a  new  piece 
may  readily  be  substituted  whenever  oxidation  has  reduced  its  strength 
or  elasticity.  (See  Fig.  179.)  Nos.  20  and  24  B.  &  S.  G.  are  the  most  use- 
ful sizes  :  the  former  is  large  enough  for  coiled  springs  for  spreading  the 
arch  (see  Figs.  158  and  160),  while  the  latter  is  suitable  for  springs  where 
less  force  is  needed.  Piano-wire  manufacturers  use  a  different  gauge,  No. 
15  piano-wire  gauge  corresponding  to  No.  20  B.  &  S. 

Nuts  may  be  made  of  German  silver,  clasp  gold,  iridio-platinum,  or 
nickel.  The  relative  hardness  and  durability  increase  in  the  order 
named.     Clasp  gold  retains  its  color  better  than  either  of  the  others. 

Screws  may  be  made  of  German  silver,  clasp  gold,  or  steel.  Their 
strength  varies  in  the  order  given.  Clasp  gold  retains  its  color  best. 
German  silver  retains  its  hardness,  and  will  wear  much  longer  if  not 
annealed  after  drawing  and  screw-cutting.  Although  it  is  softened 
in  the  process  of  soldering,  it  still  retains  sufficient  rigidity  for  most 
purposes. 

Steel  oxidizes  so  readily  in  the  mouth  that  its  use  for  screws  has 
been  practically  abandoned.  Nickel-plating  does  not  entirely  remove 
the  objection,  as  steel  will  oxidize  under  the  nickel-plating  and  peel 
it  off. 

Swaged  caps  may  be  made  of  German  silver,  platinum,  or  gold,  the 
thickness  varying  from  No.  30  to  36. 


Tools  and  Appliances  Needed. 

It  is  unnecessary  to  describe  Fig.  106. 

the  operation  of  soldering  to  any 
one  who  has  reached  this  point  in 
his  professional  education,  but  a 
few  useful  appliances  and  tools 
may  be  enumerated. 

A  soldering  pad  or  block  is 
very  easily  made  of  plaster  and 
fibrous  asbestos,  such  as  is  used  for 
investing.  By  mixing  it  thick  it 
may  be  moulded  like  putty  in  any 
form  desired. 

A  brass  or  sheet-iron  base  may 
be  made  by  cutting  out  a  round 
piece,  slitting  the  edges,  and  turn- 
ing them  up.     Such  a  block  is  soft  enough  to  stick  pins  in  to  hold  parts 
together  in  soldering. 


Soldering  block. 


156 


PRINCIPLES  OF  METAL    WORK. 


Fig.  106  shows  a  much  more  convenient  form.  A  base  of  plaster  is 
made  in  the  form  of  a  hemisphere  by  making  a  mould  from  any  kind  of 
smooth  ball.  In  use  this  is  set  in  a  ring  of  some  kind  or  in  the  mould 
reduced  to  smaller  dimensions.  The  block  can  thus  be  tilted  at  any 
angle,  and  both  hands  are  left  free  for  work. 

Fig.  107  shows  a  very  useful  soldering  block  with  clamps  for  holding 
pieces  in  soldering.  A  chemist's  filter  stand  is  of  great  conyenience  in 
a  dental  laboratory.  Fig.  107  shows  how  one  ring  may  be  used  for 
holding  the  soldering  block  at  any  convenient  height.     The  blowpipe 


Fig.  107. 


may  rest  in  another  ready  for  use.  A  ring  may  be  used  to  support  an 
invested  case  while  heating  before  soldering.  An  adjustable  arm  or 
clamp  may  be  used  to  hold  the  blowpi])e  at  any  angle,  so  that  both 
hands  are  left  free. 

The  following  tools  are  also  needed  :  Plate  shears  ;  plate  punch  ; 
flat-nose  pliers ;  wire-cutters  ;  round-nose  pliers ;  clasp-benders ;  nip- 
pers ;  spring  pliers,  large  and  small ;  small  anvil ;  riveting  hammer  ; 
Bunsen  burner ;  blowpipe  ;  soldering  clamps  ;  pin  vice  ;  jeweller's  .saw  : 
calipers  ;  soldering  copper  ;  vulcanizer  ;  flat  file  •  half-round  file ;  draw- 


TOOLS  AND  APPLIANCES  NEEDED. 


157 


plate,  round;  draw-plate,  square;  screw-plate  (Figs.  110  and  111); 
plate-gauge  (p.  38) ;  draw-tongs. 

Drawing  "Wire. — As  it  is  not  always  possible  to  obtain  wire  of  a 
desired  size,  every  dentist  should  know  how  to  draw  it.  Draw-plates 
are  made  of  hardened  steel  and  contain  a  series  of  holes  finely  graded 
from  large  to  small  (Fig.  108). 

The  change  in  size  of  holes  from  one  to  another  should  not  be  too 
abrupt.  AVire  may  be  drawn  from  a  larger  size  or  from  an  ingot 
moulded  for  the  purpose.  Ingot-moulds  are  furnished  that  will  pro- 
duce a  long  round  or  square  ingot.  The  mould  should  be  oiled  and 
warmed  before  pouring  the  metal  in  it,  so  as  to  make  a  perfect  ingot. 
After  cooling  the  ingot  should  be  reduced  in  size  by  forging.  The 
square  ingot  is  most  easily  reduced  by  holding  it  on  a  smooth  anvil  and 
hammering  the  sides  alternately.  Some  care  and  practice  is  necessary, 
as  the  ingot  cannot  be  well  drawn  out  unless  its  square  shape  is  pre- 
served. It  should  be  annealed  frequently.  Having  thus  reduced  the 
ingot  to  a  size  that  will  enter  the  largest  hole  in  the  draw-plate,  hammer 
the  corners  slightly  to  make  the  square  an  octagon. 

Large  and  strong  draw-tongs  are  needed,  and  those  should  be  selected 
which  have  short  jaws  and  long  handles,  not  less  than  eight  or  ten  inches 
in  length,  so  that  they  can  be  grasped  with  both  hands. 

The  end  of  the  ingot  or  large  wire  must  be  pointed,  so  that  it  can 
enter  the  next  smaller  hole  in  the  draw-plate,  and  project  at  least  a 
quarter  of  an  inch,  so  that  it  can  be  readily  seized  by  the  draw-tongs. 
Fasten  the  draw-plate  in  a  vise  and  apply  oil  or  beeswax  in  each 
hole. 

Seize  the  projecting  end  of  the  wire  or  ingot,  and  with  a  quick  motion 
draw  it  through  the  hole.     Repeat  the  action  with  successive  holes, 

Fig.  108. 


annealing  frequently,  till  the  wire  is  reduced  to  the  desired  size.  The 
action  of  drawing  hardens  the  wire  and  gives  it  elasticity.  If  it  is 
desired  to  retain  this  elasticity,  it  should  be  annealed  as  little  as  possible 
during  the  process,  and  not  at  all  afterward.     If  it  is  desired  to  solder 


158 


PRINCIPLES  OF  METAL   WORK. 


such  a  spring  of  German  silver  to  another  appliance,  soft  solder  should 
be  used,  as  the  heat  necessary  for  hard  solder  will  destroy  the  elasticity. 

Tubing-  or  Tubes. — Tubing  is  made  by  means  of  a  draw-plate  like 
wire.  Having  made  a  ribbon  of  the  width  and  thickness  desired,  cut 
one  end  tapering,  curl  it  slightly,  and  draw  it  through  the  largest  hole 
in  the  draw-plate.  The  diameter  of  this  hole  should  not  be  much  less 
than  the  width  of  the  ribbon.  The  edges  will  be  curled  slightly,  and 
the  operation  should  be  repeated  with  successive  holes  till  the  edges  of 
the  tube  are  in  contact  (Fig.  108).  The  tube  may  then  be  still  further 
reduced  in  size,  the  same  as  wire,  unless  the  plate  selected  was  so  thin 
that  the  edges  slide  over  each  other  instead  of  making  a  butt  joint.  For 
making  a  tube  to  fit  any  desired  size  of  wire  or  screw  the  width  of  the 
strip  should  be  a  little  more  than  three  times  the  diameter  of  the  wire 
or  screw :  No.  30  B.  &  S.  G.  plate  is  thick  enough  for  tubes  for  most  of 
regulating  appliances.  If  a  thread  is  to  be  cut  in  the  tube,  heavier  plate 
should  be  used. 

Taps  and  Dies. — For  cutting  large  screws  taps  are  used  which  are 
in  sections,  so  that  the  thread  may  be  cut  slightly  at  first,  and  then 

Fig.  109. 


deeper  by  screwing  the  sections  nearer  together  (Fig.  109).     In  cutting 
threads  in  a  nut  a  tapering  tap  is  first  used,  next  another  with  parallel 


Fig.  110. 


7      G     5     4 
Cut  screw  plate. 

sides,  but  smaller  than  the  screw  which  is  to  fit ;  then  a  tap  is  used  of 
the  full  size. 

Fig.  111. 


Jam  screw  plate. 


This  is  necessary  in  steel  and  other  hard  metals  or  alloys,  but  with 
the  softer  ones  the  threads  for  both  nuts  and  taps  may  be  cut  full  size  at 
first. 


TOOLS  AND  APPLIANCES  NEEDED.  159 

Sectional  dies  are  seldom  made  small  enough  for  dentists  and  jewel- 
lers' use,  but  screw-plates  are  provided  with  holes  of  different  sizes, 
resembling  draw-plates,  except  that  the  holes  are  screw  cut.  These  are 
known  as  cut  plates  or  jam  plates  according  as  they  actually  cut  a  V- 
shaped  spiral  groove  or  produce  it  by  pressing  into  the  surface.  (See 
Figs.  110  and  111.) 

The  most  efficient  tap  for  dentists'  use  is  a  compound  instrument 
combining  a  drill  and  a  tap.  It  is  readily  made  from  an  old  excavator, 
one  with  a  long  handle  preferred  (Fig.  112).     First  draw  the  temper; 

Fig.  112. 


Combined  drill  and  tap. 

then,  by  rotating  the  instrument  in  the  left  hand  while  the  end  rests  in  a 
notch  in  the  file-block  of  the  bench,  file  it  round  for  a  distance  of  about 
five-eighths  of  an  inch  from  the  end. 

For  one-fourth  of  an  inch  or  more  from  the  end  the  size  should  be 
such  that  the  instrument  wilt  fit  loosely  the  first  tap-hole  above  the  one 
selected  in  the  screw-plate.  For  a  space  of  one-fourth  of  an  inch  above 
that  the  instrument  should  be  of  a  size  to  enter  snugly  the  second  hole 
above,  and  be  slightly  indented  by  the  threads  as  it  is  screwed  in  the  first 
hole  above.  Flatten  the  lower  one-fourth  of  an  inch  and  shape  the  end 
as  usual  for  a  spear-pointed  drill.  Cut  the  desired  thread  in  the  second 
■one-fourth  of  an  inch  of  the  instrument.  To  do  this  well,  fasten  the 
screw-plate  in  a  vise,  and,  holding  the  instrument  at  right  angles,  screw 
it  slowly  into  the  tap  desired.  Oil  the  instrument  and  turn  it  back  and 
forth,  gradually  advancing  it  as  the  thread  is  cut.  The  die-plate  is  so 
hard  and  the  annealed  steel  is  so  soft  that  the  tap  should  be  made  with- 
out special  difficulty.  To  temper  the  tap  heat  it  to  a  cherry  red  to  a 
•distance  of  three-quarters  of  an  inch  from  the  end  and  plunge  it  in  ice- 
water  ;  this  makes  it  extremely  hard  and  brittle. 

To  draw  the  temper  and  make  the  instrument  tough  as  well  as  hard, 
first  brighten  one  side,  then  heat  the  end  in  the  Bunsen  or  alcohol  flame 
till  the  drill  portion  is  reduced  to  a  straw  color,  the  tap  to  the  slightest 
blue  obtainable,  and  the  shank  above  the  tap  to  a  spring-blue  color. 
The  drill  point  should  be  properly  shaped  by  grinding.  (See  Fig.  112, 
showing  bevelled  cutting  edges.)     Grind  the  tap  triangular  or  square. 

Cutting  Threads  on  "Wire. — Select  a  wire  which  will  fit  loosely  the 
second  hole  of  the  screw-plate  above  the  size  desired,  or  draw  wire  for  the 
purpose.  In  the  bench  vise  place  two  blocks  of  hard  wood,  and  grasp 
the  wire  so  as  to  leave  about  a  quarter  of  an  inch  exposed  (Fig.  114). 
File  the  end  slightly  pointed,  put  on  a  drop  of  oil,  apply  the  screw-plate 
so  that  the  point  of  the  wire  will  enter  the  countersunk  side ;  press 
slightly  and  revolve  the  plate  in  the  direction  indicated  by  the  thread 
about  one  turn ;  revolve  it  back  about  half  a  turn,  then  forward  again. 
By  this  time  the  thread  will  have  caught  sufficiently  to  hold  without 
downward  pressure.  Work  the  plate  forward  and  backward,  advancing 
a  little  each  time  till  the  plate  has  run  down  to  the  wooden  blocks.  Un- 
screw the  vise,  raise  the  wire  a  little,  and  proceed  as  before.  By  thus 
'exposing  only  a  slight  portion  of  the  wire  at  a  time  a  less  amount  of  it  is 


160  PRINCIPLES  OF  METAL    WORK. 

subjected  to  strain,  and  it  is  less  likely  to  bend  or  break.     The  softer  the 
wire  the  more  readily  will  the  thread  be  cut,  and  the  harder  it  is  the  more 

Fig.  113. 


Cutting  threads  on  wire. 


care  must  be  taken  to  advance  the  die-plate  only  a  little  at  each  turn, 
keeping  the  wire  well  lubricated. 

It  is  well  to  make  a  screw  several  inches  long,  from  which  pieces 
may  be   cut  off  as   needed.     Taper   the  cut   end 
slightly,  as  the  thread  is  liable  to  injury  from  the  ^^^-  l^^- 

shears  or  niiiDers  ^^^mmm^^ma 

A  square  end  may  be  filed  on  the  screw  to  fit  a 
watch-key,  or,  if  a  larger  head  is  needed,  screw  on         ^  ^taaiaiiHiiSB} 

a   square   nut   and   solder   it  (Fig.  114,  A).  Cuttlna:  tliread  on  wire : 

If  a  round  head  is  needed,  solder  a  piece  of     ^oCd-hetdTcrew!"''' '  ^' 
tubing  on  the  screw  at  any  position  desired,  and 

drill  holes  through  it  at  right  angles  for  the  insertion  of  a  pointed  in- 
strument for  turning  it  (Fig.  114,  B).  In  most  appliances  the  screw  is 
stationary  and  the  nut  turned. 

Nuts. — The  following  is  Dr.  C.  S.  Case's  description  of  his  method 

of  making  nuts:    "The  nuts  are  made    of 

JIG.  115.  five-cent  nickels,  which  are  found  to  be  of 

r^:  -  —3^^-7-7  T^^a  (^    proper  quality  and  the  thickness  to  be  easily 

Cases  guide  in  making  nuts.        cut  and  withstand  cvery  desired  force,  while 

they  suffer  no  oxidation  in  the  mouth  that 
retards  them  from  readily  gliding  upon  the  screw.  Saw  the  nickel  in 
halves,  and  mark  it  into  squares  a  little  larger  than  the  required  size  of 


TOOLS  AND  APPLIANCES  NEEDED. 


161 


Fig.  116. 


the  nut.  These  are  again  cross-marked  or  punched  in  the  centre  for  a 
guide  to  the  drill.  At  the  other  end  of  the  tap  (or  on  an  excavator 
handle)  I  make  a  screw  the  length  of  the  nut  with  an  abrupt  shoulder, 
and  square  the  shank  the  required  size  of  the  nut.  (See  Fig.  115.)  This 
when  tempered  quite  hard  will  be  found  a  valuable  and  almost  indis- 
pensable adjunct  to  the  finishing  of  these  exceedingly  small  nuts."  Screw 
the  roughly-shaped  nut  against  this  shoulder  and  file  to  the  size  and  shape. 

Dr.  Matteson's  method  of  making  nuts  •}  "  In  regard  to  making  these 
nuts  for  irregularity  cases,  I   have  found  cutting  them   out   of  solid 

nickel  and  German  silver  plate,  to  be 
drilled,  tapped,  and  squared,  a  very 
tedious  process.  The  process  may  be 
greatly  simplified  by  first  drawing  tubes 
Square  tubing  for  nuts.  Qf   platinized    silvcr   (1    part  platinum 

and  2  parts  silver),  soldering  the  joint 
with  20-carat  gold,  then  drawing  through  a  '  square-hole '  draw-plate,  in- 
serting piano  wire  in  the  tube,  thus  making  a  square  tube  with  a  round 
hole,  then  sawing  oif  enough  for  a  nut"  (Fig-  116). 

German  silver  may  be  used  instead  of  platinized  silver,  but  is  not  as 
hard.  It  is  not  necessary  to  insert  piano  wire  in  the  square  tube  in 
drawing.  Even  if  the  opening  is  reduced  very  small,  all  that  is  needed 
is  enough  to  guide  the  point  of  the  drill  in  enlarging  it. 

To  make  the  nut,  saw  off  a  short  piece  of  the  square  tube,  and  hold 
it  in  the  vise.  With  the  drill  and  tap  shown  in  Fig.  112  enlarge  the  hole 
in  the  centre  and  cut  the  thread.  In  doing  the  latter  work  the  tap  from 
left  to  right,  advancing  a  little  each  time  till  the  thread  is  cut  through 
the  length  of  the  nut.  It  is  as  easy  to  make  a  long  nut  as  a  short  one, 
and  the  greater  the  number  of  threads  in  a  nut  the  better  will  it  hold 
and  the  longer  will  it  last. 

Keys  for  fitting  the  square  ends  of  screws  may  be  made  by  selecting 


Fig.  117. 


Keys  and  wrenches. 


a  watch-key  or  small  clock-key  (Fig.  117,  A)  to  fit,  cutting  oif  the 
handle,  and  fastening  it  to  a  socket  handle  with  shellac  (Fig.  117,  B), 
To  do  this  fill  the  socket  with  powdered  shellac,  heat  the  key  enough  to 


^  Review,  vol.  iv.,  1892,  p.  566. 


11 


162 


PRINCIPLES  OF  METAL    WORK. 


soften  or  melt  the  shellac,  and  press  it  to  place.  The  key  may  be  fas- 
tened with  soft  solder  as  folloAVS :  First  brighten  the  inside  of  the  socket 
and  outside  of  the  key ;  apply  to  each  dilute  chloride  of  zinc  (tinner's 
"acid  ") ;  melt  small  pieces  of  solder  in  the  socket  till  nearly  full ;  heat 
the  key  and  press  into  place.  Pure  tin  may  be  used  for  soft  solder  in 
these  cases.  A  right-angled  key  may  be  made  by  filing  a  slot  in  the 
end  of  a  handle,  squaring  the  key-shank,  and  fastening  with  either  hard 
or  soft  solder  (Fig.  117,  C). 

A  wrench  may  be  made  by  filing  a  slot  in  the  end  of  a  flattened 
instrument  and  bending  to  any  desired  angle  (Fig.  116,  D  and  E). 

Apparatus  Employed. 

Plates. — For  making  a  simple  vulcanite  plate  to  fit  against  the 
lingual  surfaces  of  the  teeth  an  impression  should  be  taken  in  plaster, 
though  modelling  compound  will  do  in  some  cases.  By  making  a  large 
vacuum  chamber  many  of  these  simple  plates  can  be  retained  by  atmo- 
spheric pressure.  Although  plates  have  been  superseded  in  a  great 
degree,  they  are  not  only  useful  in  a  number  of  cases,  but  in  some  cases 
are  better  than  anything  else. 

Advantages. — Plates  by  their  contact  with  a  greater  number  of  teeth, 
and  also  with  the  palatine  portion  of  the  alveolar  ridge,  distribute  their 
anchorage  more  than  any  other  appliance  ;  they  are  easily  constructed. 

Disadvantages. — On  account  of  impaction  of  food  under  a  plate  it 
is  more  uncleanly  than  any  other  form  of  regulating  appliance,  hence 
necessitates  very  frequent  visits  to  the  dentist.  In  many  cases,  however, 
plates  may  be  so  constructed  as  to  be  advantageously  removed  by  the 
patient  for  cleansing. 

Fig.  118  shows  the  simplest  form  of  a  plate  for  moving  a  tooth 
lingually. 

Fig.  119  shows  a  similar  one  Fig.  119. 

for  moving  all  the  incisors  lin- 
gually. / 

r  V 


r^- 


A  tooth  may  be  moved  labially 


Fig.  118. 


by  means  of  rubber,  compressed  wood,  or  tape  between  the  edge  of  the 
plate  and  the  tooth.  The  edge  of  the  plate  should  be  made  thick,  and 
a  box  or  dovetailed  space  may  be  cut  in  it,  with  inserted  cone  bars  to 
retain  the  rubber  or  wood  (Fig.  120).  This  is  one  of  the  oldest 
appliances  on  record. 

By  boring  two  small  holes  through  the  plate  near  the  edge  a  lump  of 


APPARATUS  EMPLOYED. 


163 


rubber  may  be  tied  to  the  edge  with  floss  silk  (Fig.  121).  At  a  second 
visit  a  thicker  piece  or  two  thicknesses  of  the  same  may  be  tied  in 
place.  A  better  plan  is  to  enlarge  the  plate  at  that  point  with  gutta- 
percha (Fig.  122). 

Cut  a  dovetailed  box  in  the  edge  with  an  inverted  cone  bur,  warm 
a  lump  of  gutta-percha,  press  it  in  the  box,  put  the  plate  in  the  mouth, 
and  press  it  in  place.  The  gutta-percha  will  mould  itself  against  the 
tooth  that  has  moved,  and  thus  enlarge  the  plate  just  that  much.     A 


Fig.  120. 


Fig.  121. 


Plate  with  box  {A);  B,  rubber  or  compressed 
wood  in  box. 


Rubber  tied  on  a  plate. 


piece  of  soft  rubber  may  now  be  ligated  in  position  as  before.  At  the 
next  visit  of  the  patient  the  gutta-percha  may  be  softened  and  pressed 
again  against  the  tooth,  thus  enlarging  the  plate  a  second  time.  When 
the  tooth  has  reached  the  desired  position,  it  can  be  retained  by  the 
enlarged  plate,  but  a  better  retainer  is  shown  in  Fig.  123. 

Such  plates  may  be  advantageously  ligated  to  deciduous  molars  or 
bicuspids.     Two  holes  should  be  drilled  through  the  plate  from  the 

Fig.  123. 


Author's  retainer,  band,  and  round  wire. 


Fig.  124. 


Plate  with  gutta-percha  extension. 


Ligatures  for  securing  or  holding  plate. 


lingual  surface,  and  should  emerge  at  the  cervico-palatme  edge.  The 
holes  should  not  be  more  than  one-eighth  of  an  inch  apart.  Pass  the 
ligature  through  the  holes  as  shown  in  Fig.  124,  and  tie  firmly  around 
the  neck  of  the  tooth. 

The  plate  can  be  advantageously  used  with  the  labial  bow,  as  shown 

in  Fig.  125. 


164 


PRINCIPLES  OF  METAL    WORK. 


The  Coffin  split  plate  is  shown  in  Fig.  126.    Plates  are  advantageously 
used  for  anchoring  piano- wire  springs,  either  simple  or  coiled,  for  moving 


Fig.  125. 


teeth  in  all  directions  (Figs.  126  and  127).  The  end  of  such  spring 
should  be  flattened  or  bent  at  right  angles  for  about  one-eighth  of  an 
inch,  and  imbedded  in  the  wax  base-plate,  with  the  projecting  portion 

resting  against  the  tooth  to 
be  moved.  This  projecting 
end  will  be  securely  held  in 
plaster  while  the  wax  is  re- 
moved and  rubber  vulcanized.. 
Bands. — The  origin  of  the 
closed  band  for  regulating  ap- 
pliances is  lost  in  obscurity. 
It  was  doubtless  invented  in- 


Coffin  split  plates. 


Plate    and  wire  springs   for  self-protru- 
sion—Jackson's method. 


dependently  by  several  different  men.  The  writer  distinctly  remembers 
such  a  closed  band  with  a  hook  attached  having  been  used  in  rotating 
teeth  in  Grand  Rapids,  Mich.,  in  1863. 

The  cementing  of  a  band  on  a  tooth  has  developed  a  new  era  in  regu- 
lating appliances.     In  the  early  days  of  orthodontia  one  of  the  most  per- 


APPARATUS  EMPLOYED.  165 

plexing  problems  was  the  attachment- of  appliances  to  the  teeth.  Liga- 
tures and  clasps  were  used,  but  were  unsatisfactory,  especially  with 
partially  erupted  teeth.  Sometimes  pits  were  drilled  in  teeth  for  the  ends 
of  appliances  to  rest  in,  and  sometimes  these  pits  were  deepened  so  that 
a  screw  could  be  inserted  or  a  pin  cemented  in. 

The  invention  of  the  closed  band  cemented  on  a  tooth  renders  these 
previous  methods  unnecessary. 

The  ribbons  for  bands  should  be  rolled  from  wire  No.  13  to  16,  B. 
&  S.  gauge,  and  so  thin  that  they  can  be  easily  bent  around  a  tooth,  and 
as  wide  as  the  tooth  will  admit.  For  bicuspids  and  molars  the  thick- 
ness should  not  be  more  than  No.  36,  B.  &  S.  G.,  while  for  incisors 
the  bands  may  be  used  still  thinner.  After  rolling  the  ribbon  should 
be  annealed  and  polished. 

The  simplest  method  of  making  bands  is  thus  described  by  Prof. 
Angle  :  "  The  surface  of  the  tooth  to  be  banded  is  carefully  cleaned  by 
means   of    a   pledget   of    cotton  ^ 

moistened  in  alcohol  or  ether.  A 
loop  of  band  material  is  then 
slipped  over  the  tooth.  The  ends 
should  be  grasped  close  to  the 
tooth  with  a  pair  of  closely- 
fitting  fiat-nosed    pliers  and  the 

band    drawn     tightly    around    the       ^         ^,  band  fitted  ;£,  ready  for  soldering. 

tooth,  a  strong  burnisher  being  applied  at  the  same  time  to  make  it  con- 
form still  further  with  the  shape  of  the  tooth.  Remove  the  band,  which 
now  presents  the  appearance  shown  in  Fig.  128.  Place  a  small  bit  of 
solder  and  borax  at  the  junction  between  the  ends,  and  carry  the 
band  in  contact  with  the  flame  of  the  soldering  lamp.  After  it  is 
soldered  clip  the  ends  off,  and  the  band  is  now  ready  for  any  attachment 
which  may  be  made."  This  description  applies  equally  to  bands  of 
German  silver,  platinum,  or  platinum  faced  with  gold.  The  rubber  dam 
should  be  applied  before  cementing  a  band  on  a  tooth. 

In  soldering  such  a  band  the  projecting  ends  may  be  held  in  the 
pliers,  but  a  simpler  method  is  the  following :  Cut  off  one  end  at  a  six- 
teenth of  an  inch   from  the  p       ,nQ 
junction,    and    the    other   a 

little   longer   (Fig.   128,  A).  ^^^  ^  — 

Bend    the    longer    end    over  .    ^  j,  ^         \.f 

the  shorter,  and  pinch  them       '^  ^Sb' 
tightly  together  (Fig.  128,  B). 

With     light     spring     pliers  *        \ 

grasp  the  band  on  the  oppo-  Stea,i^ 


and    borax   on   the  junction 
and  hold  in  a  soldering  flame 


site  side,  lay  a  bit  of  solder         |  i        (        J 

K    on    thft    innntion.        '^\  (  I  ^—or 

Matteson   Cap. — ^This  is  V 

a  swaged   cap  fitting  wholly  

or  partially  over  the  cutting  Making  Matteson  caps. 

edges  or  grinding  surface  of  a  tooth,  and  extending  nearly  or  quite  to 
the  gums  or  even  under  their  free  margin.  Such  a  cap  will  adhere  to  a 
short  or  conical  tooth  much  better  than  a  band  (Fig.  129,  A).     Take  an 


166 


PRINCIPLES  OF  METAL    WORK. 


Fig.  130. 


miRtmmM"riimiiin^|wft 


impression  with  Mellott's  moldine,  and  make  a  die  and  counter-die  of 
his  metal.  If  a  harder  die  is  necessary,  take  an  impression  with 
Teague's  impression  compound  or  other  similar  material,  dry  it,  and 
fill  with  zinc  or  Babbitt  metal.  Make  a  counter-die  of  lead  or  lead 
and  tin. 

In  most  cases  a  cap  may  be  swaged  from  a  single  flat  piece  of 
metal,  but  it  is  better  in  some  cases  to  cut  and  shape  a  piece  partially 
before  swaging.  For  a  short  cuspid  cut  a  circular  piece  of  plate  having 
a  radius  equal  to  the  longest  side  of  the  tooth  ;  cut  a  slit  from  periphery 
to  centre  or  cut  out  a  V-shaped  piece  (Fig.  129,  E).  Bend  the  piece  into  a 
hollow  cone  (Fig.  129,  C)  ;  place  it  in  the  counter-die  and  swage.  For 
a  molar  it  is  best  sometimes  to  shape  the  plate  like  a  Maltese  cross  (Fig. 
129,  D),  with  the  centre  piece  as  large  as  the  occlusal  surface  and  each 
arm  slightly  wider  than  the  side  of  the  tooth.  After  swaging  the  seams 
should  be  soldered  with  a  high-grade  solder.  In  some  cases  it  is  ad- 
vantageous to  make  a  single  cap  or  chain  of  caps  for  several  teeth,  as 
for  bicuspids  and  molars  (Fig.  129,  E  and  F). 

Clamp  Bands. — Fig.  130,  a,  shows  Dr.  J.  N.  Farrar's  clamp  band, 
which  was  illustrated  in  the  Cosmos,  Jan.,  1876,  and  used  for  drawing 
the  cuspid  back.  Since  that  time  Dr.  Farrar  has 
applied  the  band  for  many  other  purposes  and 
for  the  attachment  of  other  appliances,  to  a  sin- 
gle tooth  in  some  cases,  but  more  often  to  two  or 
more  (Fig.  130,  6,  c,  d,  e).  It  is  constructed  of 
18-carat  gold  or  platinum  ribbon  made  by  roll- 
ing out  wire  to  a  thickness  of  No.  30  B.  &  S.  G. 
or  less.  To  one  end  of  the  band  is  soldered  a 
square  nut  and  to  the  other  a  "smooth  bone" 
nut.  A  headed  screw  passing  through  the  latter 
engages  with  the  former,  and  is  tightened  around 
the  teeth  by  means  of  a  wrench.  The  head  of 
the  screw  is  made  square  or  round.  If  the  lat- 
ter, it  must  be  perforated  so  as  to  be  turned  by  a 
pin  wrench  (Fig.  131).  To  prevent  the  band 
sliding  against  the  gums,  lugs  or  ear-pieces  are 
soldered  on  it  at  appropriate  places  and  bent  over  the  occlusal  or  against 
the  inclined  surfaces  of  the  teeth.  To  these  bands  are  soldered  wire 
hooks  or  staples  for  attachment  of  other  appliances,  such  as 
"push  jacks,"  "pull  jacks,"  levers,  rubber  bands,  springs, 
etc.  The  nuts  on  these  clamp  bands  are  single,  double,  or 
triple,  as  illustrated  in  Fig.  131. 

Fig.  132  shows  two  bands  adjusted  with  two  screws  work- 
ing in  a  double  nut. 

Angle's  Adjustable  Clamp  Band. — From  No.  36  band 
ribbon,  as  wide  as  the  length  of  the  crown  will  allow,  cut  a 
piece  long  enough  to  nearly  surround  a  tooth.  To  one  end 
solder  a  short  screw,  and  to  tlie  other  a  short  tube  just  large 
enough  to  pass  easily  over  the  screw.  By  means  of  a  nut 
on  the  end  of  the  screw  the  band  may  be  tightened  around 
(Fig.  133).  The  band  should  then  be  burnished  to  fit  ac- 
The  edge  should  be  slightly  bent  over  the  occlusal  surface  to 


P 


Farrar's  clamp  band. 


Fig.  131. 


Single,  double, 
and  triple 
nuts  (Far- 
rar). 

the  tooth 
curately. 


APPARATUS  EMPLOYED. 


167 


Use  of  double  nut 
(Farrar). 


prevent  the  band  sliding  against  the  gum.     To  this  clamp  band  may  be 
soldered  other  attachments. 

Bands  and  caps  should  be  soldered  with  as  high  grade  Fig.  132. 
of  solder  as  they  will  allow,  so  that  attachments  may  be 
soldered  to  them  with  a  lower-grade  solder  without  danger 
of  unsoldering  the  first  seam.  This,  however,  is  not  al- 
ways necessary  ;  with  the  skilful  use  of  the  blowpipe  solder- 
ing may  be  accomplished  on  one  side  of  the  band  without 
heating  the  other  side  to  so  high  a  temperature. 

Platinum  should  be  soldered  first  with  pure  gold,  then 
appliances  may  be  attached  with  any  grade  of  solder  they 
will  admit.  With  pure  gold  or  gold-faced  platinum,  solder 
as  high  as  22  carats  may  be  used  first,  and  lower  grades 
afterward. 

With  22-carat,  or  coin  gold,  use  20-carat  solder  first.  With 
German  silver  use  silver  plate  or  coin  silver  for  the  first  soldering,  and  for 
the  second  use  silver  solder. 

Soft  solder  may  be  used  for  attaching  piano  wire  or  springs  of  any 
kind  which  will  lose  their  temper  in  a  high  temperature. 

Hooks. — The  simplest  way  to  make  a   hook  is  to  form  it  where  the 
band  is  lapped.     When  the  band  is  bent  around  the  tooth  and  drawn 
tight  with  the  pliers,  any  point  of  junction  may  be 
selected  that   will  be  most   suitable  for  a  hook,  yig.  133. 

whether  on  the  labial  or  lingual  surface  (Fig. 
134,  a).  The  projecting  ends  may  be  bent  at  an 
acute  angle  with  the  band  instead  of  a  right  angle, 
and  after  soldering  the  hook  may  be  filed  nar- 
rower than  the  band  and  the  edges  rounded  (Fig.  Biscupid. 
134,  b). 

If  a  hook  is  needed  on  both  sides,  make  the  first  one  by  doubling  the  rib 

Fig.  134. 


Molar. 


Making  hooks  on  bands. 

bon,  as  in  Fig.  134,  c,  and  soldering  the  junction,  then  bending  it  around  the 
tooth  as  usual,  and  making  the  other  hook  wherever  desired  (Fig.  134,  d). 
A  bar  or  lug  may  be  made  by  doubling  the  band  for  a  longer  distance 
(Fig.   134).     Such  a  bar  should  be  thick   enough  Fig.  135. 

to  file  round  or  half-  round,  as  the  purpose  in  most  /       / 

cases  is  to  rest  on  an  adjoining  tooth  as  a  retainer.    rr\f      J         I 
A  round  wire  resting  on  a  tooth   touches  it  at  one        /  / 
point  only,  and  can  be  kept  clean  easily,  but  a  flat       ^ 
bar  will  retain  fluids  in  eontact  with  a  tooth  the  whole   width  of  the 
bar  (Fig.  135). 


168 


PRINCIPLES  OF  METAL    WORK. 


Soldering-  a  "Wire  to  a  Band. — A  wire  is  easily  soldered  to  any  part 
of  a  band  as  follows  :  Melt  a  small  piece  of  solder  on  the  band  wherever 
the  attachment  is  desired.  Hold  in  the  fingers  or  pliers  a  piece  of  wire 
three  or  four  inches  long,  and  rest  the  other  on  the  band  where  the  solder 
was  fused  (Fig.  136,  a).  The  band  may  rest  on  a  soldering  block  or  be 
held  in  the  soldering  pliers.  Direct  the  blowpipe  flame  on  both  wire 
and  band.  The  wire,  being  smaller  than  the  band,  will  be  heated  more 
quickly,  and  be  ready  to  attract  the  solder  as  soon  as  it  is  melted.  The 
surplus  wire  can  then  be  cut  off.  The  end  of  the  wire  may  be  stuck  in 
a  cork  or  piece  of  soft  wood  if  the  heat  is  communicated  to  the  fingers,  or 
a  short  piece  of  wire  may  be  held  in  the  long-handled  spring  pliers. 


Fig.  136. 


Fig.  137. 


^-"0  © 


Soldering  wire  to  bands. 


Farrar's  bands,  hooks,  and  staples. 


A  wire  can  be  thus  attached  to  a  band  at  any  angle..  A  wire  hook 
may  be  made  by  soldering  the  wire  at  right  angles  to  the  band,  cutting 
off  the  surplus,  and  then  bending  the  remaining  portion  in  the  shape 
desired  (Fig.  136,  b-d).  A  staple  may  be  made  by  bending  the  loose  end 
over  on  the  band  and  soldering  with  a  lower  grade  of  solder. 

Dr.  Farrar's  method  of  attaching  a  staple  or  a  lever  is  to  punch  a  hole 
in  the  band  and  insert  one  arm  of  the  staple  or  one  end  of  the  lever  to 
hold  it  in  place  for  soldering    Figs.  136,  137). 

To  Solder  a  Tube  to  a  Band. — Proceed  as  if  it  were  a  piece  of  wire 
and  cut  off  the  surplus.  To  prevent  a  tube  opening  after  it  is  attached 
care  must  be  taken  to  place  the  seam  next  to  the  band  before  soldering, 
during  which  process  the  edges  become  soldered  also.     If  the  seam  is 


Fig.  138. 


Fig.  139. 


Soldering  a  tube  to  a  band  (Angle). 


Soldering  regulating  appliances  (Farrar). 


slightly  flattened  with  a  file,  it  is  more  easily  kept  in  place  while  solder- 
ing. A  short  piece  of  tubing  may  be  attached  by  holding  it  with  a  small 
steel  instrument,  as  shown  in  Figs.  138  and  139,  or  by  holding  in  place 
with  a  spring  clamp  (Fig.  140). 


APPARATUS  EMPLOYED. 


169 


Another  method  of  attaching  a  bar,  wire,  or  tube  is  to  pres.s  the  edges 
of  the  band  slightly  into  the  soldering  block  of  plaster  and  asbestos,  and 
then  tilt  the  block  to  an  angle  of  about  30°,  so  that  the  tube,  wire,  or  bar 
when  placed  in  position  will  rest  against  the  desired  surface  and  be  re- 
tained by  gravity.  Apply  borax  and  solder  to  the  point  of  contact,  and 
direct  the  blowpipe  flame  so  that  the  parts  will  be  heated  evenly  and  the 
solder  flow  to  both  at  once.  The  operation  is  simplified  if  a  bit  of  solder 
is  first  fused  on  the  band. 

Pins  or  pieces  of  piano  wire  may  be  stuck  in  the  soldering  block  to 
hold  the  parts  in  contact. 

Two  bands  or  a  series  of  bands  may  be  attached  at  their  contiguous 
surfaces  by  placing  them  on  the  teeth  in  the  position  desired,  then  taking 
an  impression  with  modelling  compound.    The  bands  should  be  removed 

Fig.  140. 


Fig.  141. 


Soldering  a  tube  to  a  band. 

from  the  teeth  and  placed  in  the  impression,  which  should  be  filled  with 
equal  parts  of  plaster  and  sand,  marble  dust,  chalk,  or  other  suitable 
material.  Teague's  impression  compound  is  well  adapted  to  the  purpose. 
When  the  cast  is  removed  from  the  impression  the  bands  will  be  found 
in  the  exact  position  in  which  they  are  to  be  soldered  to  each  other. 
This  may  be  done  by  melting  a  small  piece  of  solder  at  each  point  of 
contact.  Where  special  rigidity  is  needed  a  stiff  wire  may  be  soldered 
on  the  labial  or  lingual  surfaces  so  as 
to  unite  all  the  bands. 

A  socket  for  retaining  the  end  of 
a  spring  or  screw  may  be  made  by 
soldering  a  short  tube  to  the  band 
vertically  or  at  whatever  angle  may 
be  best  suited  to  the  case.  A  hole 
may  be  punched  or  drilled  in  a  band  where  it  is  lapped  or  the  band  may 
be  thickened  at  any  point  for  the  same  purpose.  A  slot  may  be  made 
in  the  band  in  the  same  manner  to  retain  the  flattened  end  of  a  screw 
and  prevent  its  turning  (Fig.  141). 

Partly-made  Appliances. — To  facilitate  work  when  a  patient  is  in 
the  chair  many  partly-made  appliances  should  be  kept  on  hand,  as  follows  : 

Band  material  or  ribbdn  in  coils,  No.  31  to  No.  36,  from  l  to  ^  of 
an  inch  wide,  of  German  silver,  platinum,  etc.  (Fig.  143,  a). 


170 


PRINCIPLES  OF  METAL    WORK. 


Wire. — German  silver,  clasp  gold,  and  piano  wire  Nos.  13  to  24,  also 
iron  or  copper  binding  wire,  silver  suture  wire,  and  fine  platinum  wire. 

Partly-made  bands,  with  tube  or  wire  bar 
Fig.  142.  attached  (Fig.  143,  B  and  c).      By  placing 

such  a  partly-made  band  on  a  tooth  with 
tube  in  the  position  desired  it  may  be  drawn 
tightly  with  pliers  and  finished  as  in  Fig. 
143,  D.  The  partly-made  band  c  may  be 
finished  as  a  retainer,  e  or  F,  or  the  bar  may 
be  cut  short  enough  to  serve  only  as  a  hook  for  attachment  in  rotating  G. 
The  outer  half  of  the  tube  may  be  filed  or  ground  away  to  serve  as  a 

Fig.  143. 


Partly-made  appliances. 


notch  in  which  to  rest  a  wire  or  bow,  h.  Either  the  upper  or  lower 
portion  may  be  filed  away  so  as  to  leave  a  hook,  i. 

Adjustable  bands  (Fig.  142),  either  plain  or  with  tube  attached,  j  and  K. 

Screw  loire  (Fig.  144,  a)  should  be  kept  on  hand  a  few  inches  in  length. 
Not  more  than  two  sizes  will  be  needed  in  many  cases.  Nos.  16  and  19 
B.  &  S.  G.  are  convenient  sizes. 

Fig.  144. 


Screws  and  tubes. 


Bound  tubing  (Fig.  144,  b)  of  German  silver  for  back  teeth  and  of 
gold  for  anterior  teeth  should  be  of  several  sizes,  to  use  with  screws  or 
plain  wires.  Some  tubing  should  be  very  small  for  fine  piano  wire. 
No.  24  B.  &  S.  G. 

Flat  Tubing  (Fig.  144,  c). — This  is  seldom  needed  except  in  short 
lengths,  and  may  be  made  by  bending  a  piece  of  the  thicker  band  ribbon 
over  flat-nosed  pliers  or  a  flat  spatula  with  parallel  sides,  or  by  flattening 
a  round  tube.  It  is  useful  as  a  socket  for  a  loop  in  the  end  of  a  piano 
wire,  D,  to  keep  it  from  turning  out  of  position,  or  for  a  sliding  bar. 

Square  tubing  (Fig.  116)  for  nuts  (p.  161)  of  one  or  two  sizes. 

Nuts,  both  long  and  short  (Fig.  144,  f),  to  fit  each  size  of  screw. 


FORCES  APPLIED. 


171 


Rubber  tubing,  from  ^6  **^  T  i^ich,  g  (Fig.  161) ; 
Floss  silk,  previously  washed  ; 
Twisted  silk  and  linen  thread  ; 
Tape  for  wedging ; 
Compressed  wood  ; 

Jack-screws,  partly  made,  with  long  sheath,  which  may  be  quickly 
shortened  to  suit  any  case  in  hand  (pp.  171  and  172) ; 
Talbot  springs  (p.  174) ; 
Matteson  springs  (p.  174). 

Forces  Applied. 

Forces. — For  applying  intermittent  force  the  screw  is  more  useful 
than  any  other  appliance.  It  is  used  for  pushing  and  pulling.  A 
pushing  screw  is  generally  known  as  a  jack-screw,  and  a  pulling  screw 
as  a  "  drag-screw." 

The  Angle  jack-screw  is  the  simplest  and  easiest  to  make.  Having  de- 
cided on  the  length  needed,  cut  off  a  piece  of  screw  wire  a  little  shorter 
and  fit  it  with  a  nut.  Flatten  one  end  by  hammering,  so  as  to  spread  it 
out  wide.  In  some  cases  it  is  desirable  to  file  a  notch  in  the  flattened  end. 
Select  or  make  a  piece  of  tubing  of  such  a  size  that  the  screw  wire  will 
pass  in  it  easily  without  binding.  Flatten  one  end  of  the  tube  or  solder 
in  it  a  short  piece  of  wire  and  file  it  to  a  point. 
Insert  the  screw  in  the  tube,  and  the  jack-screw 
is  complete  (Fig.  145).  In  use  one  end  is  in- 
serted in  a  socket  or  hole  in  a  band  attached  to 
a  tooth,  and  the  other  in  a  slot  in  a  similar  band. 
Sometimes  it  is  best  to  solder  either  the  tube  or 
the  screw  to  a  band  or  some  other  appliance. 
This  jack-screw  may  be  of  any  length,  from  i 


Angle's  jack-screw. 


Fia.  146. 


(See  Figs.   154,  155). 
inch  to  2  or  3  inches. 
Angle's  drag  or  traetion  screw  is  simply  a  wire  bent  into  a  hook  at 
one  end  and  screw  cut  at  the  other, 
with   a  nut   attached,  No.   17  or  18 
B.  &  S.  G.     In  use  one  end  is  hooked 
into  a  tube  attached  to  a  band  and  the 
other  passed  through  a  tube  on  another 
band.     Turning  the  nut  will  draw  the 
teeth  toward  each  other.  (See  Fig.  146.) 


Angle's  drag-screw. 

Farrar's  Push-  and  Pull-jacks. — Figs.  147-153  show  various  push- 
and  pull-jacks  as  made  by  Dr.  Farrar.     Fig. 


147  shows  a  fish-tailed 


— -^s 


Fig.  147. 


Fig.  148. 


A 


rnriimsaim^^"- B 


jack.  A  fish-tailed  screw  engages  in  one  end  of  a  screw  tube.  A  fish- 
tailed  wire  enters  loosely  in  the  other.  The  tube  is  turned  by  inserting 
a  pointed  instrument  in  the  hole  drilled  for  that  purpose. 

Fig.    148    shows    a    spjndle-end    jack-screw    similarly    constructed, 
except  that  the  fish-tailed  piece  is  soldered  in  one  end  of  the  tube. 


172 


PRINCIPLES  OF  METAL    WORK. 


Fig.  149  shows  what  Dr.  Farrar  calls  a  nut-jack,  used  in  construction 
of  his  clamp  bands  :  the  eye  is  made  by  soldering  a  short  piece  of  tubing 
on  the  screw  and  turning  it  spherical  in  a  lathe.  The  end  beyond  the 
eye  is  filed  square  to  fit  a  key. 

Fig.  150  shows  Farrar's  simplest  form  of  screw-jack,  consisting  of  a 


Fig.  149. 


Fig.  150. 


Fig.  151. 


-=cs: 


_|GS5ssO];:>> 


"1imair°T^:=- 


fish-tailed  tube  in  which  the  screw  moves  loosely.  On  one  end  of  the 
screw  is  an  eye  and  fish-tail.  A  nut  provided  with  eyes  for  turning  fits 
on  the  screw  and  rests  on  the  end  of  the  tube. 

Fig.  151  shows  a  series  of  spindle-end  jacks  constructed  like  those 
in  Fig.  148,  except  that  both  tube  and  screw  end  in  spindle  points.    One 


Fig.  152. 


i^ 


objection  to  these  jacks  is  that  two  instruments  are  necessary  in  working 
them,  one  for  holding  and  one  for  turning. 


Fig.  154. 


Fig.  152  shows  a  "cylindrical  swivel  screw-jack."     To  one  end  of 
a  threaded   tube   is   soldered   a   hook,  and  to  the  end  of  the  screw  is 


FORCES  APPLIED. 


173 


attached  a  swivel  ending  in  a  hook.  By  turning  the  screw  by  means 
of  a  pointed  instrument  in  the  eye  the  hooks  are  drawn  toward  each 
other. 

Fig.  153  shows  a  "barrel-turning  draw-jack."  A  piece  of  plate  is 
bent  twice  at  right  angles,  A,  and  through  the  middle  third  is  inserted 
a  wire  hook,  aS*.  It  is  then  soldered  to  the  extremity  of  the  threaded 
barrel  or  tube,  B.  The  hooked  screw  engages  in  this  tube,  which  is 
turned  by  inserting  a  wrench  in  the  square  opening  at  A.  To  prevent 
wabbling  while  being  operated  the  hooks  are  bent  so  that  the  draught 
will  be  in  a  direct  line  with  the  screw. 

Application  of  the  Jack-screw. — The  Angle  jack-screw  is  varied 
easily  in  length  by  changing  the  length  of  the  tube.  It  can  be  applied 
in  many  different  ways,  among  which  are  the  following :  Fig.  154  shows 
the  use  of   a  very  long  jack-screw,  moving  an  incisor  forward  (Fig. 

Fig.  155. 


155),  spreading  the  arch.      The  application  of  Farrar's  screw-jack  is 
shown  in  Figs.  156  and  157. 


Fig.  156. 


Fig.  157. 


Application  of  fish-tail  and  spindle- 
jack  (Farrar). 


Jacks  and  clamp  bands  (Farrar). 


The  Talbot  spring  is  made  as  follows  :  Drive  a  piece  of  piano  wire 
in  the  bench  or  hold  it  in  the  vise,  and  around  this  wind  another  piece 
of  piano  wire  by  holding  each  end  Avith  pliers.  Make  two  or  more 
turns  ;  then  bend  the  wire  at  right  angles  along  the  coil  to  a  point 


174 


PRINCIPLES  OF  METAL    WORK. 


opposite  the  beginning,  then  again  at  right  angles  in  the  same  plane  as 
the  other  end  (Fig.  158).     This  latter  is  not  necessary  unless  there  are 


Fig.  158. 


Fig.  159. 


Talbot  spring. 

several  coils.     Piano  wire  No.  15,  equal  to  No.  20  B.  &  S.  G.,  is  stiff 
enough  for  most  cases. 

Occasionally  a  spring  of  smaller  or  of  larger  wire  will  be  needed, 
but  not  often.  German-silver  or  clasp-gold  wire  may 
be  used  for  such  a  spring,  but  the  elasticity  is  not  so 
great. 

The  Matteson  spring  differs  from  the  Talbot  spring 
in  having  two  coils  instead  of  one  (Fig.  159). 

The  Coffin  spring,  used  in  a  split  plate  for  spreading 
the  arch,  consists  of  a  piano  wire  No.  20  B.  &  S.  G.  bent  with  clasp- 
benders  into  the  general  shape  of  the  letter  W,  as  shown  in  Fig.  160. 
The  ends  are  flattened  or  bent  at  right  angles  for  retention  in  the 
vulcanite. 

Fig.  160.  Fig.  161. 


Matteson  spring 


CofBn  spring. 


f[| 


Rubber  tubing  for  bands. 


For  rubber  bands  use  French  tubing,  from  \  inch  in  diameter  to  ^  or 
less,  cutting  them  wider  or  narrower  according  to  the  amount  of  force 
needed.  Bands  \  inch  in  diameter  are  the  most  useful  (Fig.  161). 
Bands  made  from  large  tubing  are  often  so  thick  as  to  take  up  too  much 
room  and  spread  teeth  apart. 

Bands  may  be  made  from  rubber  dam  by  cutting  with  two  sizes  of 
punches,  or  by  first  cutting  a  hole  with  a  punch  and  trimming  around 
it  with  scissors. 

Compressed  wood  is  useful  for  spreading  teeth  apart  or  for  moving 
a  tooth  in  any  direction  in  connection  with  a  plate  or  other  appliance. 
Select  a  fine-grained  wood  and  compress  it  laterally  in  a  vise  or  with 
large  pliers.  The  wood  of  floss-silk  spools  is  good  for  the  purpose. 
Tupelo-wood  is  highly  recommended,  being  already  compressed  as  sold 
by  dealers.  Any  dry  wood  will  swell  when  wet,  and  compressed  wood 
will  swell  much  more. 


FORCES  APPLIED. 


175 


The  swelling  of  pellets  of  cotton  or  of  cotton  tape  folded  in  two  or  more 
thicknesses  will  spread  teeth  apart  or  move  a  tooth  from  some  fixed  position. 

Rubber  strips  or  wedges  of  differ- 
ent thicknesses   may  be  used  for  the  Fig.  165. 
same    purposes.       To    move    one    or 
more  teeth  by  means  of  compressed 

Fig.  162. 


Twisted  ligatures  of  silk,  linen,  or  wire. 
Fig.  163. 


Twisting  wire  (Case). 
Fig.  164. 


Angle's  instrument  for  compressing  and 
elongating  wire. 


wood,  cotton,  tape,  or  strip  of  rubber  the  material  may  be  confined  between 
the  teeth  or  between  the  edge  of  a  plate  and  a  tooth.  A  box  or  mortise 
cut  in  the  thickened  edge  of  a  plate  will  hold  such  material  more  securely. 
Silk  or  linen  ligatures  are  very  useful  for  moving  teeth  slowly.  If 
a  ligature  of  floss  silk  be  tied  tightly  around  two  teeth  not  in  contact,  or 


176 


PRINCIPLES  OF  METAL    WORK. 


from  a  tooth  to  some  fixed  point  on  a  plate  or  other  appliance,  the  tooth 
or  teeth  will  be  moved  slightly  by  compression  of  the  peridental  mem- 
brane, and  held  thus  till  absorption  takes  place. 

By  frequently  renewing  such  ligatures  teeth  may  be  moved  some  dis- 
tance. A  twisted  ligature  of  silk  or  linen  is  more  efficacious,  because  it 
tightens  when  wet  on  account  of  the  swelling  of  the  fibres,  and  thus 
continues  to  act  for  some  time  after  being  put  in  position.  The  longer 
such  a  twisted  ligature  is,  the  more  force  it  will  have.  Its  greatest 
effect  is  shown  in  Fig.  162,  where,  after  being  looped  around  one  hook, 
the  two  strands  are  twisted  around  each  other  in  an  opposite  direction  to 
the  natural  twist  of  the  thread,  before  being  tied  to  another  hook  or  tooth. 

Twisted  wire  ligatu7'es  are  very  efficacious.  By  looping  a  copper 
wire  over  two  pins  or  hooks  the  parallel  wires  may  be  twisted  around 
each  other,  once  or  twice  a  day,  by  inserting  an  excavator  or  pointed 
instrument  between  them,  or  a  square  nut  may  be  first  put  on  one  wire 
and  the  twisting  done  with  a  wrench,  as  devised  and  used  by  Dr.  C.  S. 
Case  (Fig.  163). 

Pinched  Wire. — A  new  method  of  applying  force  has  been  introduced 
by  Prof.  Angle — the  elongation  of  a  straight  wire  by  compressing  it  in 
one  or  more  places  from  day  to  day  by  means  of  round-nose  pliers  made 
especially  for  the  purpose  (Fig.  165).  German-silver  wire  No.  18  is  a 
suitable  size. 

Application  of  Hooks,  Tubes,  etc. — The  chief  use  of  a  hook  on  a 
band  is  for  rotation  by  attaching  a  rubber  band  or  twisted  ligature  to 

Fig.  166. 


Fig.  167. 


Plate  and  band  for  rotating. 


the  hook  and  extending  it  to  a  plate  (Fig.  166),  or  to  a  hook  on  another 
tooth  (Fig.  167),  or  to  a  labial  or  lingual  bow  (Fig.  174). 


Fig.  168. 


Fig.  169. 


In  some  cases  it  is  necessary  to  make  two  hooks  on  one  band,  and  extend 
a  rubber  band  from  each  to  some  firm  point  of  attachment,  as  in  Fig.  172. 


FORCES  APPLIED. 


177 


Double  rotation   may  be  accomplished  by  means  of  two  hooks  and 
two    bands.      Figs.    168    and    1,69    show    double    rotation  in    opposite 


Fig.  170. 


Fig.  171. 


directions,  and  Figs,  170  and  171  in  the  same  direction.  Fig.  172 
shows  the  use  of  hooks  for  attachment  of  rubber  bands  for  drawing 
in  a  prominent  incisor. 

It  will  be  noticed  that  the   anchor  bands  have  each  a  round  bar 
soldered  to  the  buccal  surface  to  increase  the  anchorage. 


Fig.  172. 


Fig.  173  shows  how  the  author,  following  the  suggestion  of  Dr. 
Angle,  elongated  non-occluding  bicuspids  and  molars  and  brought 
them  into  occlusion    by  means  of  rubber  bands  ligated  to  the  lower 


Fig.  173. 


Author's  plan  of  occluding  bicuspids  and  molars. 

and  extended  to  hook  bands  on  the  upper  teeth.    One  or  two  extra  bands 
were  ligated  on  each  tooth  to  be  used  in  case  of  breakage  of  the  first. 

12 


178 


PRINCIPLES  OF  METAL    WORK. 
Special.  Appliances. 


Tubes. — The  attachment  of  a  tube  to  a  band  serves  so  many  uses  as 
to  have  almost  revolutionized  the  practice  of  orthodontia.  Figs.  174 
and  175  show  its  use  for  retaining  the  end  of  the  labial  and  lingual  bows. 

Fig.  175. 


Fig.  174. 


Labial  and  lingual  bows. 


Angle's  drag-sorew. 


Fig.   176  shows  its  use  with  the  drag-screw.     Fig.  178  shows  its 
use  in  making  up  an  appliance  for  spreading  the  arch. 


Fig.  176. 


Fig.  178. 


Lugs  on  angles. 
Fig.  177. 


Appliance  for  double  rotation.  Tube  and  piano  wire  for  rotation  (Angle). 

Fig.  179. 


Tube  and  piano  wire  for  rotation  (Angle). 


Fig.   177   shows   its    use   for   double   rotation.      In  this   appliance 
(Angle's)  care  must  be  taken  to  make  the  tubes  short  and  solder  them 


SPECIAL  APPLIANCES. 


179 


to  the  labio-buccal  line  angle  of  the  band.  A  piece  of  No.  24  B.  &  S.  G. 
piano  wire  inserted  in  the  tubes  will  rotate  the  teeth.  The  author  has 
found  it  necessary  in  some  cases  to  solder  lugs  on  the  disto-lingual  sur- 
faces of  the  bands  to  touch  upon  the  lateral  incisors  and  prevent  the 
teeth  from  being  rotated  out  of  the  arch. 

Figs.  179  shows  the  use  of  the  tube  as  a  socket  to  insert  a  lever 
of  piano  wire  for  rotation.  Fig.  180  shows  the  use  of  the  tube  for 
holding  a  retaining  Avire  for  a  tooth  which  has  been  moved  into  the 
line  of  the  arch  either  labially  or  lingually.  Provision  for  such  reten- 
tion may  be  made  by  attach- 
ing such  a  tube  before  the  Fig.  181. 
tooth  is  moved  (Fig.  182), 
so  that  when  the  tooth  is  in 
place  a  wire  can  be  inserted 
for     retention.        Dr.    Angle 

Fig.  180. 


Ketainer  (Talbot 


Providing  in  advance  for  retention. 


secured  this  wire  by  drilling  a  small  hole  through  one  side  of  the  tube 
and  the  retaining  wire  and  inserting  a  small  pin. 

The  author  has  found  it  a  good  plan  to  cement  the  wire  in  the  tube. 
A  short  tube  soldered  vertically  to  a  band  serves  as  a  socket  for  the  end 
of  a  jack-screw  or  spring.  A  hole  drilled  or  punched  in  a  tube  or  a  slot 
serves  the  purpose  in  many  cases. 

Another  use  of  tubes  or  bands  is  to  serve  as  hooks  for  attachment  of 
rubber  bands  in  retracting  cuspids  or  bicuspids,  as  shown  in  Fig.  182. 

Fig.  182. 


Author's,  modification  of  diiilford  &  aiiplianie 


When  the  desired  retraction  has  been  accomplished  the  tubes  serve  to 
hold  the  ends  of  a  labial  bow,  from  which  rubber  bands  may  be 
extended  for  propulsion  or  rotation  (Fig.  183). 


180  PRINCIPLES  OF  METAL    WORK. 

A  tube  soldered  to  one  or  more  bands  serves  as  a  socket  for  holding 

Fig.  183. 


Further  use  of  same  tubes  for  holding  bow. 


one  end  of  piano  wire  (Fig.  184),  while  the  other  is  utilized  for  moving 
teeth  in  different  directions  (Figs.  184,  185). 


Fig.  184. 


Tube  band  and  spring  appliance  (Matteson). 
Fig   185. 


Author's  appliance,  close  bite. 


A  flat  tube  for  the  insertion  of  the  looped  end  of  a  spring  will  hold  it 
more  firmly  for  pressing  on  the  buccal  or  labial  surfaces  of  teeth  (Fig.  186). 


SPECIAL  APPLIANCES. 


181 


Appliances  for  Extruded   Teeth. — An   appliance   for  pushing  an 
extruded   tooth  into  its  socket  is  readily  constructed  as   follows  :   Fit 


Fig.  186. 


Fig.  187. 


Flat  tube  for  piano-wire  spring. 


Appliance  for  reducing  extrusion. 


wide  bands  to  the  two  adjacent  teeth,  and  solder  a  tube  to  the  lingual 
and  labial  surfaces  of  each  band  (Fig.  187).  When  these  bands  are 
firmlv  cemented  on  the  teeth,  connect  the  labial  tubes  and  also  the 
lingual  tubes  with  stiff  wires,  preferably  cemented  in  the  tubes.  From 
the  labial  wire  or  bar  extend  a  rubber  band  or  a  twisted  ligature  over 
the  cutting  edge  or  occlusal  surface  of  the  extruded  tooth,  and  attach  it 
to  the  lingual  bar.  If  the  extruded  tooth  is  of  such  shape  that  the 
rubber  band  will  not  stay  in  place,  cement  a  swaged  cap  on  the  occlusal 
surfiice  and  make  a  notch  in  it. 

The  construction  of  this  appliance  is  simplified  as  follows :  Instead 
of  tubes,  solder  on  the  labial  and  lingual  surfaces  of  one  band  stiff 
wires  long  enough  to  reach  to  the  next  tooth  beyond  the  one  extruded. 
To  make  the  other  band,  first  double  the  band  material,  then  about  Jg 
of  an  inch  from  the  doubled  end  bend  each  part  at  right  angles  and 
solder  the  parts  in  contact.  Finish  the  band,  cutting  off  the  projecting 
ends  about  ylg  of  an  inch  from  the  band. 

A  notch  is  to  be  made  in  the  upper  side  of  each  projection,  and 
where  the  band  is  cemented  to  the  tooth  these  notches  form  hooks  in 
which  to  rest  the  ends  of  the  wires  extending  from  the  other  band  (Fig. 
188,  d).  The  rubber  band  is  more  easily  attached  to  these  bars  than  to 
the  ones  previously  described,  because  it  can  be  slipped  over  the  end  of 


Fig.  188. 


Fig.  189. 


Details  of  appliance  for  reducing  extrusion.  Author's  appliance  for  reducing  extrusion. 

each  wire  where  it  rests  in  the  hook.  When  the  extruded  tooth  has  been 
pushed  up  in  its  socket,  it  may  be  retained  by  substituting  a  small  plat- 
inum or  silver  wire  for  the  rubber  band  or  ligature,  but  a  better  plan  is 
to  make  three  bands  for  the  three  teeth,  solder  them  together  where  they 
are  in  contact,  and  cement  them  to  the  three  teeth. 


182 


PRINCIPLES  OF  METAL    WORK. 


Appliances  for  Forcible  Eruption. — For  this  operation  an  appliance 
is  needed  which  is  just  the  reverse  of  the  other :  for  drawing  down  an 


Fig.  190. 


Author's  appliance  for  elongating  broken  tooth. 

incisor  either  partially  erupted  or  broken,  swage  caps  for  the  contiguous 
teeth,  and  connect  them  by  a  wire  extending  from  the  cutting  edge  of 
one  to  the  cutting  edge  of  the  other  (Figs.  190  and  191). 

Fig.  191. 


Author's  appliance  for  forcible  eruption. 

On  the  tooth  to  be  elongated  cement  a  band  made  as  in  Fig.  190,  or 
one  to  which  hooks  have  been  soldered  on  both  labial  and  lingual  sur- 
faces. From  the  labial  hook  extend  a  slender  rubber  band  or  twisted 
ligature  over  the  connecting  wire  and  secure  it  to  the  lingual  hook.  The 
movement  must  be  slow  to  avoid  rupturing  the  pulp  at  the  apical  foramen. 
The  bar  forms  a  limit  bevond  which  the  tooth  cannot  be  drawn.     The 


Fig.  192. 


Fig.  193. 


Forcible  eruption  (Angle). 


tooth  may  be  retained  Iby  substituting  a  platinum  or  silver  wire  for  the 
rubber  band,  but  better  by  three  bands. 


SPECIAL  APPLIANCES. 


183 


Fig.  192  shows  Prof.  Angle's  appliance  for  elongation  or  forcible 
eruption.  Its  construction  is  very  simple,  consisting  of  a  tube  soldered 
to  a  band  on  any  convenient  tooth.  From  the  tube  a  stiff  wire  extends 
across  the  space,  and  is  hooked  over  the  cutting  edge  of  the  next  con- 
venient tooth.  From  this  bar  a  rubber  band  is  extended  to  a  pin 
anchored  in  the  tardy  tooth  or  to  a  hook  soldered  to  a  cap  cemented  on 
the  tooth. 

Fig.  193  shows  a  similar  appliance  in  which  lower  teeth  are  used  for 
anchorage. 

Fig.  194  shows  a  case  treated  under  the  author's  directions  in  the 
infirmary  of  the  College  of  Dentistry  of  the  University  of  California, 


Fig.  194. 


Fig.  195. 


by  a  senior  student.  The  occlusion  was  brought  about  in  three  or 
four  weeks,  Fig.  195.  During  the  performance  of  mastication  the 
patient  unhooked  the  rubber  bands,  so  as  not  to  produce  too  severe  a 
strain  on  the  alternating  teeth. 

Application  of  the  Drag-screw. — Angle's  drag-screw  is  one  of  the 
most  simple  and  effective  appliances.     It  consists  of  a  stiff  wire  screw 

Fig.  196. 


Angle's  drag-screw. 


cut  at  one  end  and  bent  into  a  hook  at  the  other.  Fig.  196,  a,  shows  the 
appliance;  Fig.  196,  h,  shows  its  use  for  retracting  a  cuspid.  Double 
anchorage  is  secured  by  soldering  a  long  tube  to  a  molar  and  a  bicuspid 
band.  By  this  means  the  two  teeth  are  so  firmly  yoked  together  that 
tipping  is  prevented,  and  the  teeth,  if  moved  at  all,  must  be  dragged 
bodily  through  the  process. 

The  attachment  to  the  cuspid  varies  according  to  the  movement  re- 
quired. If  the  attachment  is  made  as  in  Fig.  198,  right  side,  the  tooth 
will  be  rotated  as  well  as  drawn  backward.  If  the  hook  is  attached  as 
in  Fig.  197  or  Fig.  198,  left  side,  the  tooth  will  be  drawn  backward 
without  rotatina:. 


184 


PRINCIPLES  OF  METAL    WORK. 


Fig.   199  shows  the  author's  use  of  the  drag-screw  for  reducing  a 
prominent  cuspid  and  at  the  same  time  making  room,  on  the  principle 


Fig. 197. 


of  drawing  two  wedges  toward  each  other.  The  cuspid  forms  one  wedge 
and  the  lingual  bar  another.  The  drag-screw,  hooked  in  the  cuspid  band 
and  drawn  through  the  bar  by  the  nut,  forces  the  two  wedges  together. 


Fig.  200  shows  another  use  of  the  drae:-screw. 


Fig.  199. 


Author's  appliance  for  making  room  and  drawing  cuspid  in. 
Fig.  200. 


Drawing  cuspid  in  (Angle). 


SPECIAL  APPLIANCES. 


185 


The  Jackson  Crib. — The  crib  devised  by  Dr.  V.  H.  Jackson  of 
New  York  is  essentially  a  pecnliar  clasp  which  clings  readily  to  a  molar 
or  bicuspid,  and  to  which  springs,  screws,  etc.  may  be  attached. 

Its  construction  is  as  follows  :  First,  a  piece  of  German  silver  plate, 
No.  30,  is  fitted  to  the  lingual  or  buccal  surface  of  a  molar  or  bicuspid. 
It  should  be  made  concave  with  contouring  pliers  or  by  striking  a 
rounded  instrument  while  it  rests  upon  a  piece  of  lead,  or  against  it,  so  that 
it  will  fit  snugly  against  the  rounded  surface  of  the  tooth,  especially  at  the 
cervical  margin.  This  is  best  accomplished  by  exaggerating  the  concavity 
a  little,  so  the  piece  will  touch  the  tooth  only  at  its  edges.  (See  A,  Fig.  201.) 

Fig.  201. 


The  Jackson  crib  and  base  wire. 


The  clasp  portion  is  made  of  piano  wire  No.  20  B.  &  S.  G.,  or  of  hard 
drawn  German  silver  wire  nnannealed,  slightly  larger,  by  first  bending 
it  at  right  angles  (Fig.  202),  leaving  the  width  between  parallel  sides 
equal  to  the  antero-posterior  width  of  the  tooth  to  be  clasped.  The  part 
that  is  to  clasp  the  neck  of  the  tooth  is  then  so  bent  with  clasp-benders 
that  it  will  be  perfectly  adapted  to  the  curve  of  the  cervex  (Fig.  203). 
Both  arms  of  the  wire  are  then  bent  at  nearly  a  right  angle  at  a  proper 
distance  to  cause  them  to  pass  over  the  grinding  surface  of  the  tooth  or 
the  points  of  contact  with  the  adjacent  tooth,  and  again  bent  in  the  same 
manner  to  extend  toward  the  neck  of  the  tooth  on  the  lingual  side  (Fig. 
204).     The  ends  are  next  bent  toward  each  other  near  the  gum-line 


Fig.  202. 


Fig.  203 


Fig.  204. 


O^ 


over  the  piece  of  metal  ])reviously  described,  as  seen  at  A  in  Fig.  201, 
and  tacked  with  soft  solder.  The  crib  thus  made  clasps  the  tooth  at  the 
cervico-l)uccal  and  cervico-lingual  portions,  and  is  prevented  from  sliding 
up  too  far  by  the  wires  passing  over  the  occlusal  surface. 

If  a  spring  is  to  be  atta(!he<l  to  the  crib,  one  end  should  be  held  in 
contact  with  the  contoured  piece  of  metal  and  the  ends  of  the  crib  wire. 


186 


PRINCIPLES  OF  METAL    WORK. 


All  portions  to  which  it  is  desired  to  liave  the  solder  adhere,  having 
been  previously  brightened,  should  be  moistened  with  dilute  chloride  of 
zinc  (tinner's  acid).  A  small  lump  of  soft  solder  laid  in  contact  and 
touched  with  a  heated  soldering  copper  will  flow  around  and  unite  all 
the  parts,  rounding  itself  so  as  scarcely  to  need  further  smoothing. 

Most  of  Jackson's  appliances  consist  primarily  of  a  base-wire,  No. 
12,  13,  or  14  B.  &  S.  gauge,  connecting  cribs  on  two  opposite  molars 
or  bicuspids,  and  bent  in  a  bow  corresponding  to  the  lingual  surfaces  of 
the  teeth  (Fig.  201 ).  To  this  base-wire  are  soldered  springs  for  moving 
teeth  in  diiferent  directions  according  to  the  requirements  of  individual 
cases.  By  placing  all  the  parts  on  a  cast  the  end  of  the  base-wire  may 
be  readily  held  in  contact  with  the  crib-plate  and  wire  by  the  thumb 
protected  by  a  wad  of  paper  while  the  soft  solder  is  fused  M'ith  the  sol- 
dering copper.  The  end  of  a  spring  wire  may  be  held  at  the  same  time 
so  as  to  be  united  with  the  rest.  A  spring  may  be  soldered  to  any  part 
of  the  base- wire  by  binding  the  two  together  with  line  copper  wire  and 
soldering  with  soft  solder.  Dr.  Jackson  has  suggested  an  improvement 
on  this :  First,  a  piece  of  jSTo.  30  German  silver  plate  is  tinned  on  one 
side  by  flowing  tin  or  soft  solder  over  it  with  a  soldering  copper.  It  is 
then  cut  into  strips  about  one-thirty-second  of  an  inch  in  width,  to  be 
used  in  place  of  the  copper  wire.  To  unite  two  wires  one  of  these  strips 
is  wound  spirally  around  them  (Fig.  205),  with  tinned  surface  next  the 


Fig.  205. 


wires.     Upon    applying    soft   solder   with    the    soldering   copper    it   is 
attracted  by  the  tinned  surface  and  readily  flows  between  and  around 


Fig.  206. 


Fig.  207. 


both  wires  and  strip,  uniting  them  firmly  with  a  joint  less  bnlky  than 
can  be  made  in  any  other  way. 

Figs.  206  and  207  show  various  applications  of  the  crib  and  springs. 


SPECIAL  APPLIANCES. 


187 


On  account  of  the  deterioration  of  piano  wire  through  oxidation,  Dr. 
Jackson  has  ahuost  abandoned  its  use  in  favor  of  hard-drawn  German 
silver  wire,  using  Nos.  12,  13,  and  14  for  base-wire,  ISTos.  21  and  22  for 
cribs,  and  Nos,  15,  16,  17,  and  18  for  springs,  according  to  the  length 
and  force  needed,  long  springs  being  made  of  larger  wire  than  short 
ones.  These  cribs  and  springs  may  also  be  made  of  clasp-gold  wire 
united  with  hard  solder. 

Figs,  208  and  209  show  another  form  of  crib  sometimes  used  by  Dr. 


Fig.  208. 


Fig.  209. 


Jackson.  German  silver  or  piano  wire  about  No.  20  B.  &  S.  gauge  is 
bent  so  as  to  enclose  a  sufficient  number  of  teeth  to  secure  firm  anchor- 
age ;  then  one  or  both  ends  are  extended  so  as  to  act  as  springs  for 
moving  teeth  in  various  directions. 

The  wire  may  be  bent  with  pliers  to  fit  against  the  teeth  of  a  plaster 
cast,  though  it  is  better  for  a  novice  to  use  a  metal  die.  At  proper 
intervals  cross  wires  are  looped  over  the  buccal  and  labial  wires,  so  as 
to  extend  across  the  point  of  contact  of  teeth  and  prevent  the  crib 
impinging  on  the  gum. 

The  CoflBn  Split  Plate  for  Spreading-  the  Arch.' — An  impression 
is  taken  with  modelling  compound,  and  allowed  to  remain  in  the  mouth 
till  quite  hard.  Special  care  is  taken  not  to  put  too  much  material  in 
the  palatine  portion  of  the  tray,  as  it  will  be  forced  backward  and  distort 
the  impression  at  the  iiecks  of  the  teeth. 

When  the  cast  is  made  trim  away  slightly  the  portions  representing 
the  gum  in  the  interdental  spaces  of  the  molars  and  bicuspids,  both 
buccally  and  lingually,  so  that  the  plate  which  covers  the  crowns  of 
these  teeth  may  project  slightly  into  these  spaces  and  clasp  more  tightly. 

Make  a  wax  base-plate  covering  the  palatine  portion  of  the  cast  and 
the  entire  crowns  of  bicuspids  and  molars  to  the  bucco-gingival  borders. 
The  palatine  portion  should  be  smoothed  as  for  a  vulcanite  denture,  but 
the  wax  on  occlusal  surfaces  should  be  moulded  by  pressing  with  the 
finger,  so  as  to  reproduce  the  cusps  and  depressions.  The  finished  plate 
will  thus  articulate  well  with  the  inferior  teeth  for  masticating  purposes. 

The  spring  should  be  made  of  piano  wire  No.  20  B.  &  S.  G.,  which 


^  Introduced  at  the  International   Medical   Congress,  London,  Aug., 
Walter  H.  Coffin  of  London. 


1881,  by  Mr. 


188 


PRINCIPLES  OF  METAL    WORK. 


Fig.  210. 


corresponds  to  No.  15  of  piano-wire  gauge,  and  should  be  bent  in  the 
form  and   size   shoMai   (Fig.  210).     The   whole   spring  should   be  also 

curved  to  fit  the  lingual  surface  of  the  plate, 
and  the  two  arms  must  be  so  bent  that  when 
they  are  imbedded  in  the  wax  plate  near  the 
necks  of  the  bicuspids  the  rest  of  the  spring 
will  be  free  from  the  surface.  The  ends  of  the 
arms  should  be  flattened  or  bent  at  right  angles 
for  about  one-eighth  of  an  inch,  so  that  they 
may  be  more  firmly  held  by  the  vulcanite.  If 
thick  tin-foil  is  burnished  on  the  wax  covering 
the  occlusal  surfaces  of  the  teeth,  and  also  under  the  spring,  it  will  line 
the  plaster  mould  so  that  the  rubber  vulcanized  against  it  will  need  no 

Fig.  211. 


Coffin  split  plates. 

further  polish.     As  it  is  difficult  to  place  the  tin  under  the  spring  on  the 
wax  plate,  it  is  better  to  wait  till  the  flask  is  opened,  and  then  burnish 

it  on  the  lingual  portion  of  the 
P'iG.  212.  plaster  mould.     After  the  plate 

is  vulcanized,  smoothed,  and 
polished  it  should  be  divided  in 
the  median  line  with  a  fine  saw 
and  the  edges  slightly  rounded 
to  prevent  wounding  the  mucous 
membrane  (Fig.  211).  When  it 
is  tried  in  the  mouth  the  lateral 
portions  should  slide  over  the 
bicuspids  and  molars  so  as  to 
grasp  them  firmly.    After  the  plate  has  been  worn  a  few  days  the  spring 


SPECIAL   APPLIANCES. 


189 


should  be  spread  by  pulling  the  halves  of  the  plate  slightly  apart. 
When  again  inserted  in  the  mouth  the  spring  will  be  compressed  so  as 
to  exert  pressure  laterally  and  spread  the  arch.  For  spreading  the  lower 
arch  the  plate  should  be  made  as  in  Fig.  212. 

The  spring  should  conform  to  the  lingual  surfaces  of  the  incisors,  but 
should  not  touch  them.  The  Coffin  split  plate  is  often  made  to  cover 
only  the  palatine  surface  of  the  mouth  and  fit  against  the  necks  of  the 
teeth.     The  cast  should  be  trimmed  at 

the  interdental  spaces,  so  that  projec-  ^^^^-  2^3- 

tions  of  the    plate  will    enter  slightly 
between  the  teeth  to  hold  it  in  place. 

Fiff.  213  shows  the  writer's  modi- 
fication  of  the  Coffin  spring  plate  for 
moving  incisors  forward.  A  Coffin 
spring  is  inserted  on  each  side  of  the 


plate  as  near  the  necks  of  the  teeth  as 
possible,  one  end  of  each  spring  being 
near  the  lateral  incisors  and  tlie  other 
near  the  molars.  It  is  sawed  cross- 
ways  apart,  so  that  the  anterior  portion 
can  spring  away  from  the  posterior  and 
move  incisors  forward.  A  wire  nib 
should  project  from  the  anterior  por- 
tion between  the  central  incisors,  or  the  edge  of  the  plate  should  rest 
under  projecting  bands  on  the  incisors  to  prevent  sliding  out  of  place. 
Fixed  Appliances  for  Expansion. — Fig.  214  shows  the  writer's 
combination  for  spreading  the  arch.  It  is  called  a  combination  because 
it  is  made  up  of  bands,  tubes,  and  Angle's  jack-screw  or  Talbot's  spring. 

Fig.  214. 


Author's  modification  of  Coffin  split  plate. 


Author's  combination  for  expansion. 

It  is  easily  constructed  as  follows  :  Wide  bands  are  made  for  two 
teeth  on  each  side,  generally  the  first  bicuspid  and  first  molar,  but  often 
for  the  cuspid  and  second  bicuspid.  For  the  cuspid  a  swaged  cap  is 
often  better  than  a  band.     On  the  buccal  surface  of  a  bicuspid  or  molar 


190 


PRINCIPLES  OF  METAL    WORK. 


band  a  tube  is  soldered  for  subsequent  use.  Each  pair  of  bands  is  joined 
to  a  bar  soldered  to  the  lingual  surface.  This  bar  is  preferably  made  of 
clasp  gold,  but  German  silver,  No.  22  or  thicker,  may  be  used,  and  it 
should  be  about  one-eightli  of  an  inch  wide.  Holes  are  punched  in  it 
about  one-eighth  of  an  inch  apart. 

The  construction  is  simplified  by  placing  the  bands  on  a  cast  of  equal 
parts  of  plaster  and  marble  dust,  sand,  or  asbestos.  A  piece  of  solder 
is  melted  on  the  lingual  surface  of  each  band.  The  cast  is  tilted  on  the 
soldering  block,  so  that  the  bar  when  placed  in  position  will  be  retained 
by  its  own  Aveight.  When  the  blowpipe  flame  is  applied  the  bar  will  be 
heated  first,  and  will  attract  the  solder  as  soon  as  it  is  melted,  and  thus 
be  firmly  secured  to  the  bands. 

The  bar  may  be  long  enough  to  impinge  on  a  tooth  anterior  or  pos- 
terior to  the  banded  teeth,  so  that  a  greater  number  will  move. 

Fig.  215. 


Author's  expander  with  Angle's  jaclv-scre\N 


Either  a  screw  or  a  spring  may  be  used  for  force.     The  Angle  jack- 
screw  is  the  simplest  form  for  intermittent  pressure  (Fig.  215).     The 


Fig.  216. 


Author's  expander  for  lower  arch. 

end  of  the  sheath  or  tube  should  be  pointed  and  the  end  of  the  screw 
flattened  and  forked.     By  placing  the  pointed  end  of  the  sheath  or  tube 


SPECIAL  APPLIANCES. 


191 


in  a  hole  in  the  bar  on  one  side,  and  one  prong  of  the  forked  end  in  a 
hole  in  the  opposite  bar,  the  force  may  be  applied  by  turning  the  nut. 

On  account  of  the  jack-screw  being  in  the  way  of  the  tongue  the 
Talbot  spring  is  of  less  annoyance.  The  spring  should  be  bent  so  as 
to  conform  to  the  arch  of  the  palate,  but  should  not  touch  the  mucous 
membrane  (Fig.  217).  For  the  lower  arch  the  Matteson  spring  is  better 
(Fig.  216).  .  ,  . 

The  ends  are  bent  so  as  to  enter  the  holes  in  the  bars,  and  pass  in 
just  far  enough  to  remain  in  position.  At  subsequent  visits  of  the 
patient  the  spring  is  removed,  spread  slightly,  and  replaced. 

As  there  are  several  holes  in  each  bar,  the  position  of  the  jack-screw  or 

Fig.  217. 


Matteson  caps  in  place  of  bands  in  appliance 
for  expanding  arch. 


Angle's  appliance  for  expansion. 


spring  may  be  varied  according  to  the  needs  of  the  case.  Two  jack-screws 
or  two  springs  may  be  used  at  once  if  desired,  one  at  each  end  of  the  bar. 

When  the  arch  is  spread  sufficiently,  the  jack-screw  or  spring  is 
replaced  by  a  stiff  curved  wire  (Fig.  214,  c)  for  retention.  The  tubes 
on  the  buccal  surfaces  of  the  bands  may  then  be  utilized  for  the  appli- 
cation of  a  "labial  bow  "  for  various  uses  (Fig.  214,  a,  h).  The  ends  of 
the  bow  may  be  bent  in  bayonet-shape  or  supplied  with  thread  and  nut. 

Fig.  218  shows  Angle's  appliance  for  expanding  the  arch.  It  is 
made  up  as  follows  :  Having  decided  how  many  teeth  are  to  be  moved 
on  each  side  of  the  arch,  a  band  is  fitted  to  the  anterior  and  posterior 
teeth  of  each  phlanyx.  These  may  be  either  closed  or  adjustable  bands, 
and  each  should  have  a  short  tube  soldered  on  the  lingual  surface.  These 
bands  should  be  cemented  to  the  teeth,  and  the  anterior  and  posterior 
tubes  should  be  connected  by  wires  extending  along  the  lingual  surfaces 
of  the  intervening  teeth.  These  wires  are  best  kept  in  place  by  cement- 
ing them  in  the  tubes.  Collars  made  of  short  sections  of  tubing  should 
have  been  previously  soldered  on  these  wires  at  regular  intervals.  The 
force  for  spreading  the  arch  is  gained  from  a  jack-screw.  The  object  of 
the  collars  on  the  side  wires  is  to  keep  in  place  the  ends  of  the  jack- 
screw,  which  may  be  shifted  in  position  according  to  where  the  greatest 
force  is  needed.  Two  jack-screws  may  be  used,  one  at  each  end  of  the 
appliance. 


192 


PRINCIPLES   OF  METAL    WORK. 


Bo^ws. — The  labial  bow  extending  along  the  buccal  and  labial  surfaces 
of  the  teeth  is  one  of  tlie  oldest  appliances  for  attachment  of  ligatures  or 
rubber  bands  for  moving  teeth.  The  ends  of  the  bow  have  been  secured 
in  various  ways — by  ligatures,  by  imbedding  in  a  plate,  by  soldering  to 
bands  or  cribs,  or  by  the  insertion  in  tubes  soldered  to  bands  or  vulcan- 
ized into  a  plate.  The  bow  is  made  of  a  fiat  strip  of  plate  or  of  round 
or  half-round  wire.  ■  Round  wire  is  best,  as  it  presents  no  surface  to 
rest  on  the  teeth,  which  are  therefore  more  easily  kept  clean. 

Fig.  219  shows  a  bow  of  round  wire  attached  to  a  vulcanite  plate. 
The  ends  of  the  bow,  bent  at  right  angles,  should  pass  between  the  teeth 

Fjg.  219. 


Labial  bow  and  plate  (Kingsley). 


through  some  convenient  space  or  over  the   occlusal  surface  through 
some  space  left  when  the  superior  and  inferior  teeth  are  in  contact. 


Fig.  220. 


^■ 


in)  /^f^j 


i4lil||AV 


Fig.  220  also  shows  the  manner  of  attaching  rubber  bands  for  moving 
teeth  outward  or  rotating.  In  many  cases  it  will  be  necessary  to  ligate 
such  a  plate  to  bicuspids  or  temporary  molars. 


SPECIAL  APPLIANCES. 


193 


Fig.  221  shows  an  almost  universal  use  of  such  an  appliance  for 
moving  teeth  labially  or  Ungually  or  for  rotating. 

The  best  method  of  securing  the  ends  of  the  labial  bow  is  to  insert 
them  in  tubes  or  bands  cemented  to  molars,  deciduous  or  permanent,  or 


Fig.  221. 


Bow  for  superior  protrusion. 


to  bicuspids.     In  some  cases  it  is  best  to  solder  a  longer  tube  to  two 
bands  which  shall  be  cemented  to  two  contiguous  teeth  for  better  anchor- 


FiG.  222. 


Labial  and  lingual  bow. 


age,  or  two  such  bands  may  be  soldered  together  at  points  of  contact 
and  a  tube  soldered  to  but  one  of  them. 


13 


194 


PRINCIPLES  OF  METAL    WORK. 


If  the  bow  is  intended  merely  for  attachment  of  ligatures  or  rubber 
bands,  the  ends  may  be  bent  in  bayonet  shape  to  prevent  their  extending 
too  far  through  the  tubes,  or,  as  Prof.  Angle  suggests,  the  posterior  ends 
of  the  tubes  may  be  pinched  and  closed.  The  best  way,  however,  is  to 
cut  a  thread  on  each  end  of  the  bow  and  apply  a  nut.  If  a  nut  is 
applied  at  each  end  of  the  tube  and  tightened,  the  bow  is  held  very 
rigidly  in  position.  Tlie  bow  may  be  enlarged  by  loosening  the  nuts 
behind  the  tubes,  or  made  smaller  by  tightening  anterior  ones. 

Fig.  221  shows  how  protrusion  of  anterior  teeth  may  be  reduced  by 

Fict.  223. 


Labial  and  lingual  bows  for  all  movements. 

tightening  nuts  behind  the  tubes.  In  such  a  case  the  anterior  portion 
of  the  bow  should  rest  in  notches  or  against  lugs  on  bands  cemented 
to  central  incisors.       The  simplest  method  of  providing  such  notches 

Fig.   224. 


is  to  join  the  ends  of  the  band  (Fig.  222,  A)  on  the  labial  surface ;  then, 
having  soldered  the  parts  in  contact  for  about  one-sixteenth  of  an  inch, 
to  cut  off  the  surplus  and  file  a  notch  in  the  portion  left.  Fig.  222 
also  shows  another  way  to  make  a  notch  from  a  tube. 


SPECIAL  APPLIANCES. 


195 


A  lingual  bow,  the  ends  of  which  are  inserted  in  tubes  on  the  lingual 
surfaces  of  the  same  bands  that  anchor  the  labial  bow,  is  of  great  ad- 
vantage in  many  cases  (Fig.  224). 


Fig.    225. 


Labial  bow  and  hook  band  for  lotation 


This  lingual  bow  may  be  secured  by  bending  the  ends  in  form  of 
hooks  for  insertion  in  the  tubes  (Fig.  224),  or  by  screw-cutting  and  ap- 


Fio.    226. 


Lingual  bow  and  hook  band  foi  rotation  (author). 

plying  behind  or  at  both  ends  of  the  tubes.  The  lingual  tube  may 
be  dispensed  with  if  in  making  the  band  the  projecting  ends  are 
stiffened  with  solder  and  a  hole  punched  or  drilled  through  (Fig. 
223,  A). 

Fig.  222  shows  the  two  bows  used  together  for  the  same  purposes  as 
the  plate  and  bow  in  Fig.  220  for  all  movements  of  single  teeth. 

This  appliance  has  the  advantage  of  greater  stability  and  cleanliness. 

Figs.  224,  225,  and  226  show  the  bows  used  for  attachment  for  bands 
for  rotating  a  tooth. 

Fig.   227  shows  the  use  of  the  lingual  bow  for  moving  incisors  for- 


196 


PRINCIPLES  OF  METAL    WORK. 


ward,  and  Fig.  228  its  use  in  double  rotation,  while  it  retains  the  widened 
arch  after  the  use  of  spring  or  jack-screw. 


Fig.   227. 


Lingual  bow  for  moving  incisors  forward  (Matteson). 

Fig.  229  shows  one  of  Dr.  Farrar's  methods  of  attaching  the  labial 
bow,  or,  as  he  calls  it,  the  "  long  band,"  to  clamp  bands.  The  bow  is 
then  used  for  attachment  of  ligatures  or  rubber  bands. 

Fig.  228. 


Lingual  bow  loi  retention  of  expanded  aich  and  anchorage  m  rotation. 
Fig.  229.  Fig.  230. 


Labial  bow  and  clamp  band  (Farrar). 


Labial  bow  and  clamp  band  (Farrar). 


Fig.  230  shows  another  method.  Clamp  bands  are  secured  by  screws 
on  the  lingual  surfaces  of  the  teeth.  On  each  end  of  the  bow  is  soldered 
a  smooth  bore  nut  or  tube.     Through  this  a  screw  passes  to  a  nut  sol- 


SPECIAL  APPLIANCES. 


197 


dered  to  the  buccal  surface  of  the  clamp  band.     By  turning  these  screws 
the  size  of  the  bow  is  lessened  for  reducing  superior  protrusion. 

Fig.  231  shows  how  Dr.  C.  S.  Case  of  Chicago  used  two  labial  bows 
at  the  same  time,  one  for  the  retraction  and  the  other  for  propulsion,  the 


Fig.  231. 


Case's  appliance  for  moving  roots. 

object  being  to  hold  back  the  cutting  edges  of  incisors  and  cuspids  with 
one  bow,  while  pushing  the  roots  and  the  enclosing  alveolar  process  for- 
ward with  the  other.  The  following  is  Dr.  Case's  description  of  the 
construction  :  "  In  constructing  the  appliance  for  forcing  the  roots  and 
adjoining  bone  of  the  anterior  teeth  forward  wide  German  silver  banding 
material  for  the  teeth  should  be  selected  that  is  five-  or  six-thousandths 
of  an  inch  in  thickness.  This  should  be  fitted  to  the  crowns  of  the 
anterior  teeth  near  the  margins  of  the  gum,  perhaps  extending  beneath 
the  margins  on  the  proximal  sides. 

"The  bars  of  No.  18,  E.  S.  G.  wire,  slightly  flattened,  should  be 
attached  to  each  of  the  bands  in  an  upright  position,  and  bent  so  as  to 
lie  along  the  anterior  surface  of  the  crowns  from  the  apex  (cutting  edge) 
to  where  the  bars  join  the  band ;  here  they  should  take  a  direction  some- 
what parallel  to  the  gum,  but  free  from  the  surface  to  about  one-six- 
teenth (or  a  quarter)  of  an  inch  above  its  margin,  at  which  point  they 
should  be  flattened  or  thinned  so  as  to  be  more  readily  bent  forward  and 
firmly  clasped  around  a  rigid  bar  (labial  bow)  which  is  made  to  extend 
from  anchorage-tubes  attached  to  the  posterior  teeth  by  wide  bands. 

"This  bar  (labial  bow),  which  should  be  very  rigid,  is  drawn  without 
annealing  from  No.  12  extra  hard  German  silver  wire  to  No.  18  (E.  S.  G.). 
The  ends  are  threaded  in  the  No.  4  hole  of  the  Martin  screw-plate,  and 
the  central  portion  is  slightly  flattened  in  the  rollers.  Then  it  should 
be  bent  so  as  to  rest  when  in  proper  position  in  the  unclasped  ends  of 
the  upright  bars  that  have  been  left  open  to  receive  it.  Before  placing 
it  in  position  the  nuts  should  be  screwed  on  to  work  at  the  anterior  ends 
of  the  tubes. 

"The  apparatus  is  completed  by  a   second   bar  much  smaller  and 


198 


PRINCIPLES  OF  METAL    WORK. 


thinner  than  the  first,  but  proportionately  light,  which  rests  in  depres- 
sions in  the  upright  pieces  along  the  occluding  ends  of  the  teeth.  The 
ends  of  the  fulcrum  bar  are  threaded  and  passed  through  tubes  that  are 
soldered  to  the  anchor  bands  on  each  side  below  the  lower  bar-tubes 
with  nuts  which  work  posteriorly  to  the  tubes. 

"  The  force  expended  at  the  ancliorage  attachments  is  largely  neutral- 
ized by  the  reciprocating  influence  of  the  two  forces,  and  this  reciproca- 
tion is  always  equal  to  the  power  used  on  the  fulcrum  bar  in  preventing 
movement  of  the  occluding  eiicls  of  the  crowns." 

Fig.  232. 


Figs.  232,  233,  and  234  show  half-tone  prints  of  casts  of  face  and 
teeth,  showing  change  in  occlusion  of  the  teeth  and  also  in  contour  of 
the  face  by  moving  the  roots  forward. 


SPECIAL  APPLIANCES. 


199 


Fig.  235  shows  the  details  of  the  appliance. 

By  reversing  the  action  of  these  bows,  as  shown  in  Fig.  236,  the 


Fig.  235. 


Fig.  237. 


roots  of  incisors  can  be  forced  back.  In  this  case  the  lower  bow  is  the 
more  rigid,  and  the  anterior  portion  is  placed  under  hooks  in  the  lower 
ends  of  the  upright  bars.     The  moving  force  is  in  the  upper  bow,  which 


200 


PRINCIPLES   OF  METAL    WORK. 


rests  on  the  anterior  surface  of  the  upper  ends  of  the  upright  bars. 

The  nuts  of  the  lower  bow  are  placed  anterior  to  the  tubes,  and  those 

of  the  upper  bow  behind. 

Figs.  237  and  238  show  the  result  of  such  an  appliance  both  on  the 

position  of  the  teeth  and  contour  of  the  face. 

Fig.  239  shows  Farrar's  use  of  the  labial  bow  for  holding  the  cutting 

edges  of  incisors  while  moving  the  roots  forward  by  pressing  against  the 

lingual  cervex  with  two  jack-screws 
Fig.  239.  joined  to  a  bar.     The  bow  and  bar 

rest  in  U-shaped  lugs  on  the  inci- 
sors. The  labial  bow,  called  by 
Dr.  Farrar  "  the  long  band,"  is 
hooked  at  each  end  into  clamp 
bands.  Each  jack-screw  is  sup- 
plied with  a  hook  which  enters  a 
loop  in  the  clamp  band. 

Fig.  240. 


Farrar's  appliance  for  moving  roots  forward. 

Fig.  240  shows  the  principle  of  the  action. 

Fig.  241  shows  Farrar's  use  of  the  labial  bow  for  drawing  back  the 
roots  of  superior  incisors  while  the  cutting  edges  are  held  in  place  by  a 

bar  and  braces  on  the  lingual 
Fig.  241.  surface.     It  is  simply  the  reverse 

of  the  other  appliance.  The  bar 
rests  in  U-shaped  lugs  at  the  cut- 
ting edges  of  the  incisors,  and  is 
held  by  braces  extending  to  and 
resting  in  loops  on  the  lingual 
surfaces  of  the  clamp  bands. 
The  bow  rests  in  U-shaped  lugs 

Fig.  242. 


Farrar's  appliance  for  moving  roots  back. 

on  the  labial  cervex  of  the  incisors.     One  end   is  hooked  to  a  clamp 
band  on  one  .side,  and  from  a  loop  in  the  other  a  screw  extends  to  a 


SPECIAL  APPLIANCES. 


201 


double  nut  on  the  buccal  side  of  the  other  clamp  band.  By  turning  this 
screw  force  is  brought  to  bear  on  the  roots  of  the  incisors,  so  as  to  move 
them  backward,  compressing  the  process  behind  them. 

Fig.  242  shows  a  sectional  view. 

Fig.  243  shows  the  bow  as  used  by  Dr.  Angle,  and  Fig.  244,  as  used 
by  the  writer  in  1888  for  elongating  anterior  teeth. 

Fig.  24?.. 


F-.HA 


On  each  first  molar  or  second  bicuspid  is  cemented  a  band  with  a 
horizontal  buccal  tube  ;  on  each  cuspid  is  cemented  a  band  with  a  hook 
turned  downward  ;  and  on  each  incisor  that  needs  elongating  is  cemented 
a  band  with  a  hook  turned  up. 


Fig.  244. 


The  ends  of  an  elastic  wire  bow  are  inserted  in  the  buccal  tubes  and 
passed  viiider  the  cuspid  hooks.  The  anterior  portion  is  then  used  for 
the  attachment  of  slender  rubber  bands  or  twisted  ligatures  extending  to 
the  incisor  hooks,  or  is  sprung  up  over  the  hooks  themselves. 

When  the  teeth  have  been  elongated  as  much  as  desirable  the  same 
appliance  may  be  still  used  as  a  retainer. 

Fig.  245  shows  the  use  of  the  labial  bow  of  the  elastic  wire  for  for- 
cibly elongating  bicuspids  and  a  molar,  and  at  the  same  time  forcing 
inferior  incisors  into  their  sockets. 

A  hollow  crown  is  fitted  to  the  last  lower  molar  on  each  side.  This 
crown  should  be  high  enough  to  open  the  bite  the  distance  desired.  To 
the  buccal  surface  of  each  crown  is  soldered  a  horizontal  tube  open  at 
its  upper  surface.  To  each  tooth  which  it  is  desired  to  raise  is  cemented 
a  band  with  a  buccal  hook  turned  downward.  To  each  tooth  which  needs 
depressing  is  cemented  a  band  with  a  hook  turned  upward.  A  bow  of 
elastic  wire  is  fitted  to  the  arch,  its  ends  inserted  in  the  buccal  tubes  of 
the  hollow  crowns,  its  front  fitted  in  the  incisor  hooks,  and  its  sides  sprung 


202 


PRINCIPLES  OF  METAL    WORK. 


under  the  bicuspid  and  molar  hooks.    When  the  desired  movements  have 
been  accomplished  the  same  appliance  may  be  used  as  a  retainer. 

Fig.  245. 


Case's  appliance  for  raising  occlusion. 

Occipital  Cap. — For  cases  of  superior  protrusion  in  which  there  is  not 
sufficient  anchorage  in  the  mouth  a  cap  and  bit  may  be  made  as  follows : 
Let  a  seamstress  or  some  member  of  the  patient's  family  construct  a  cap  of 
two  pieces  of  cloth,  each  shaped  like  Fig.  246.     The  seam  should  be  along 


Fig.  246. 


the  dotted  line,  and  the  other  edges  should  be  hemmed.  Dress  hooks 
should  be  sewed  at  a  and  6.  Silesia  or  some  similar  cloth  is  suitable. 
To  make  the  bit  (Fig.  248)  first  make  a  cast  of  the  teeth,  then  mould  one 
thickness  of  wax  over  the  labial  surface  of  the  teeth  to  be  moved,  and  let 
the  wax  extend  over  the  occlusal  surfaces  and  slightly  over  the  lingual. 
In  the  anterior  surface  of  the  wax,  on  a  line  just  above  the  occlusal  sur- 
faces, imbed  a  piece  of  elastic  German  silver  or  nickel-plated  wire.  No.  12, 
about  4  inches  long,  bent  in  the  middle  to  conform  to  the  curve  of  the 
teeth  involved  and  project  from  the  corners  of  the  mouth.  The  ends 
should  be  bent  in  the  form  of  the  hooks,  and  should  project  so  far  that 
rubber  bands  extending  to  the  cap  will  not  impinge  on  the  cheeks.  Warm 


SPECIAL  APPLIANCES. 


203 


the  wire,  press  it  slightly  in  the  wax,  and  mould  wax  over  it  till  covered 
and  all  inequalities  of  the  wax  surface  filled  up.  The  case  is  flasked  and 
a  vulcanite  piece  made  like  the  wax  model.  The  long  wire  may  project 
from  the  sides  of  the  flask  or  may  be  bent  temporarily  against  the  sides 
of  the  cast,  so  as  to  go  in  the  flask  and  be  straightened  out  after  vulcan- 


FiG.  247. 


Author's  form  of  cap  and  bit. 

izing.  After  smoothing  and  polishing  try  the  "bit"  in  the  patient's 
mouth,  and  see  that  the  vulcanite  does  not  impinge  on  the  inferior  in- 
cisors nor  on  any  superior  incisors  that  are  not  to  be  moved.  Bend  the 
projecting  ends  so  that  they  will  conform  to  the  contour  of  the  cheeks, 
but  will  not  touch  them.  Place  the  cap  on  the  back  of  the  head  (Fig.  247). 
For  force  use  round  elastic  silk-covered  cord,  about  -^  of  an  inch  in  di- 
ameter. Tie  a  knot  in  one  end,  and  secure  it  in  one  of  the  hooks  on  the 
cloth  cap ;  extend  it  forward  over  one  hook  of  the  bit  and  back  to  the 
other  hook  on  the  cap. 

It  is  more  convenient  to  have  an  assistant  fit  another  elastic  cord  on 
the  other  side  of  the  head  at  the  same  time.  One  strand  of  the  cord  may 
be  sufficient ;  if  so,  tie  a  knot  in  it  behind  the  second  hook.     Generally 

Fig.  248. 


more  force  is  needed ;  if  so,  extend  the  cord  from  the  second  hook,  a 
second  time  over  the  hook  of  the  bit,  then  back  to  the  first  hook  on  the 
cloth  cap,  and  secure  it  by  a  knot. 

The  direction  of  the  force  may  be  varied  by  the  number  of  strands. 


204 


PRINCIPLES  OF  METAL    WORK. 


If  the  teeth  need  to  be  pushed  up  in  their  sockets,  arrange  the  cord  in 
three  upper  strands  and  one  k^wer.  If  the  line  of  movement  should  be 
lower,  arrange  three  lower  strands  and  one  upper. 

To  Dr.  Kingsley  must  be  given  the  credit  of  first  using  an  occipital 
appliance  for  retracting  and  shortening  the  incisors  in  1866.^ 

Figs.  249  and  250  show  Angle's  occipital  appliance  for  use  in  cases 
of  superior  protrusion.  Adjustable  bands  (Fig.  250,  D)  with  buccal  tubes 
are  attached  to  opposite  molars.      In  these  tubes  are  inserted  the  ends  of 

Fig.  249. 


a  labial  bow,  to  the  anterior  part  of  which  is  soldered  a  short  wire  with  a 
rounded  end.  The  bow  has  also  two  small  collars  or  hooks  soldered  near 
the  cuspid  region.  The  anterior  portion  of  the  bow  rests  in  notches  in 
the  projecting  ends  of  bands  on  the  central  incisors.  A  ''yoke"  or  "bit," 
shown  in  Fig.  250,  A,  has  a  short  section  of  tubing  soldered  to  the  mid- 
dle, so  that  it  can  be  applied  to  the  projection  of  the  bow  when  in  place. 
Rubber  bands  from  the  hooks  on  each  end  extend  above  and  below  the 
•ear  to  the  cap  on  the  back  of  the  head. 

As  the  bow  is  pressed  backward  it  will  carry  the  projecting  teeth 
with  it.  One  advantage  of  this  appliance  is  that  if  the  teeth  are  not  in 
a  regular  arch,  they  will  be  forced  to  conform  to  the  shape  of  the  labial 
bow.  The  appliance  is  to  be  worn  at  night  and  out  of  school-hours. 
Rubber  bands  ligated  to  the  collars  on  the  bow  and  extended  over  the 
tubes  on  the  molar  bands  serve  for  retention  during  the  daytime. 
Bicuspids  may  be  moved  outward  by  rubber  bands  from  the  sides  of 
the  bow. 

The  writer  has  found  it  best  to  screw  cut  the  ends  of  the  bow  and 
apply  nuts  behind  the  molar  tubes. 

To  avoid  destroying  the  stiffness  of  the  German  silver  bow  in  hard  sol- 
dering the  spur  in  front,  he  finds  it  best  to  first  solder  such  a  spur  to  a 
small  piece  of  tubing  with  liard  solder,  then  attach  the  tube  to  the  bow 
with  soft  solder.    To  do  this  put  the  tube  T  in  position,  apply  a  drop  of 

^  Kingsley's  Oral  Deformities,  p.  134,  Fig.  66. 


SPECIAL  APPLIANCES. 


205 


chloride  of  zinc,  put  a  small  piece  of  soft  solder  at  the  opening  of  the 
tube,  and  hold  in  a  small  flame.  As  the  solder  melts  it  will  flow  between 
the  tube  and  wire.  If  the  bow  is  made  of  clasp  gold,  it  can  be  hard 
soldered  without  injury. 

Chin  Retractor. — For  a  chin  cap  or  cup  for  reducing  prognathism 
or  correcting  lack  of  anterior  occlusion  take  an  impression  of  the  chin 


with  very  soft  modelling  compound  or  plaster.  A  large  impression- 
tray  may  be  remodelled  for  the  purpose  by  flattening  its  palatine  por- 
tion, or  for  use  with  plaster  a  wax  or  gutta-percha  tray  may  be  moulded 
to  the  chin.     The  operator's  hand  itself  might  be  used. 

If  the  impression  be  taken  in  Teague's  impression  compound  or  some 
similar  material,  it  may  be  dried  and  the  zinc  or  Babbitt  metal  poured 
in  it  directly  for  making  a  die.  Otherwise  a  model  must  be  made  for 
moulding  in  sand. 


206 


PRINCIPLES   OF  METAL    WORK. 


The  cup  may  be  made  of  German  silver  or  of  aluminum.  The  latter 
is  better  on  account  of  its  lightness.  The  cup  should  be  swaged  and 
trimmed  as  shown  in  Fig.  251.     Hooks  may  be  soldered  or  riveted  on 


Fig.  251. 


at  the  upper  edge  in  whatever  position  will  give  the  most  direct  strain 
from  the  cap,  according  to  the  direction  required. 

Fig.  252  shows  an  appliance  used  by  the  writer  for  forcing  the  infe- 


FiG.  252. 


Author's  appliance  for  depressing  inferior  Incisors. 


rior  incisors  into  their  sockets.  It  is  useful  in  cases  in  which  the  inferior 
incisors  bite  upon  the  gums  back  of  the  superior  incisors,  or  upon  the 
cervico-lingual  portions  of  the  teeth  themselves,  and  either  cause  those 
teeth  to  protrude  or,  when  they  protrude  already,  prevent  their  being 
moved  backward. 

Upon  a  zinc  die  a  cap  is  swaged  to  fit  over  the  cutting  edges  of  the 
inferior  teeth.  To  this  is  soldered  a  stiff  elastic  wire  so  bent  as  to  extend 
out  of  the  corners  of  the  mouth  and  not  interfere  with  the  lips.  The 
ends  should  be  bent  in  the  form  of  hooks.  If  German  _  silver  wire  is 
used  for  this  purpose,  it  should  be  united  with  the  cap  with  soft  solder, 


SPECIAL  APPLIANCES. 


207 


as  the  high  heat  necessary  with  silver  solder  will  deprive  it  of  its  elas- 
ticity. Piano  wire  nickel-plated  may  be  used.  The  chin-piece  is  made 
as  described  on  page  206,  but  need  not  be  so  large.  Rubber  bands  from 
the  hooks  above  to  hooks  or  buttons  on  the  chin-piece  will  force  the 
teeth  into  their  sockets.  To  prevent  the  chin-piece  sliding  forward  a 
piece  of  tape  should  extend  from  it  around  the  neck  of  the  patient. 

Retainers. — The  simplest  retainer  for  a  single  tooth  is  made  by  sol- 
dering a  round  wire  to  the  labial  or  lingual  surface  of  a  band  (Fig.  256, 
a),  and  cementing  the  band  on  the  tooth.  A  round  wire  is  much  better 
than  the  flat  bar  used  by  many,  for  it  touches  the  tooth  only  at  one 
point,  as  shown  at  Fig.  254,  and  is  easily  kept  clean,  while  the  bar 
covers  considerable  surface,  and  decay  is  liable  to  take  place  under  it 
during  the  long  time  it  must  be  worn. 

Fig.  255  shows  Guilford's  retainer,  made  by  soldering  two  bands 


Fig.  253. 


Fig.  254. 


Fig.  255. 


Fig.  256. 


together.  Several  bands  may  be  united  for  the  same  purpose.  To  unite 
them  in  proper  position  place  them  on  the  teeth  and  take  an  impression 
in  modelling  compound.  Put  the  bands  in  the  impression  in  the  posi- 
tions shown  by  their  imprint.  Make  a  cast  of  plaster  and  sand,  marble 
dust,  or  asbestos.  This  will  show  the  bands  in  their  proper  position, 
when  their  contiguous  surfaces  may  be  united  with  solder. 

For  retaining  a  rotated  tooth  solder  a  wire  so  that  it  will  project 
laterally  and  rest  on  the  labial  or  lingual  surface  of  the  next  tooth.  It 
is  best  in  many  cases  to  solder  such  a  wire  on  both  labial  and  lingual 
surfaces. 

For  method  of  soldering  wires,  tubes,  etc.  to  bands  see  page  168. 

Figs.  257  and  258  show  a  retainer,  claimed  by  both  Dr.  Angle 
and  Dr.  Talbot,  made  by  cementing  a  wire  in  a  tube  on  a  band.     Such 


Fig.  257. 


Fig.  258. 


a  tube  may  be  soldered  to  a  band  that  serves  also  some  other  purpose  in 
moving  the  tooth,  and  when  the  tooth  has  moved  the  wire  can  be  inserted 
for  retention. 

Fig.  259  shows  Guilford's  band  and  wire  retainer,  made  by  soldering 
bands  to  the  extremities  of  a  round  wire,  and  used  for  retaining  incisors 


208 


PRINCIPLES  OF  METAL    WORK. 


that  have  been  moved  backward.  An  impression  should  be  taken  with 
the  bands  on  the  teeth,  and  a  cast  made  for  holding  the  bands  while  the 
wire  is  soldered  in  the  exact  position  desired. 

Fig.  260  shows  a  similar  appliance  of  Angle's  for  retaining  teeth  which 
have  been  moved  forward.  The  ends  of  the  bow  rest  in  pits  in  the  first 
molars  or  in  holes  punched  in  bands  cemented  on  those  teeth. 


Fig.  259. 


Fig.  260. 


Either  of  these  retainers  may  be  used  in  cases  in  which  some  incisors 
have  been  moved  labially  and  some  lingually,  by  ligating  them  to  the 
retaining  wire  with  fine  platinum  or  silver  suture  wire. 

Fig.  261  shows  Dr.  C.  S.  Case's  twisted-wire  retainer.  A  fine  wire 
of  copper,  platinum,  or  silver  is  looped  from  one  hook  to  another,  and 
by  means  of  an  instrument  placed  between  the  wires  or  by  using  a 
twisted  wrench  on  a  square  nut  previously  placed  on  one  of  the  wires. 


Fig.  261. 


Fig.  262. 


Fig.  262  shows  a  crib  retainer  often  used  by  Dr.  Jackson,  though  Dr, 
Farrar  gives  the  credit  of  its  suggestion  to  Dr.  W.  H.  Atkinson.^  The 
wire  is  bent  with  pliers  and  clasp-benders  to  fit  the  buccal,  labial,  and 
lingual  surfaces  of  the  teeth  accurately.  This  can  be  done  best  on  a  metal 
die.  Cross  wires  extend  at  intervals  from  one  wire  to  the  other  to  hold 
them  against  the  teeth,  and  also  to  prevent  the  crib  pressing  on  the 
gums. 

^  Farrar,  vol.  i.  p.  000,  note. 


SPECIAL  APPLIANCES.  209 

An  expanded  arch  can  be  retained  by  an  atmospheric-pressure  plate, 
tut  better  by  substituting  a  cross-bar  for  the  jack-screw  or  a  stiff  wire 
for  a  spring. 

Many  appliances  are  of  such  shape  that  they  can  be  worn  as  retainers  : 
jack-screws,  drag-screws,  bows,  and  in  other  cases  rubber  bands  and 
twisted  ligatures,  may  be  substituted  by  platinum  or  silver  suture  wire. 

14 


CHAPTER   lY. 

MOULDING  AND  CARVING  PORCELAIN  TEETH. 

By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 


The  general  use  of  porcelain  teeth  in  dentistry  began  about  1825. 
Previous  to  that  date  the  materials  and  means  employed  in  the  con- 
struction of  artificial  dentures  were  confined  to  the  various  methods  of 
setting  human  teeth,  the  teeth  of  sheep,  and  forming  dentures  of  hip- 
popotamus tusks,  walrus  and  elephant  ivory,  etc.  The  part  of  the  human 
tooth  used  by  the  dentists,  except  in  transplantation,  was  the  crown 
portion,  properly  so  called.  A  lost  tooth  was  replaced  by  one  of  its  own 
class,  attention  being  paid  to  matching  the  natural  teeth  in  such  particu- 
lars as  shape,  size,  color,  and  quality. 

There  were  several  methods  of  introduction,  as  follows  :  pivoting, 
by  ligatures,  with  springs,  and  on  bases.  The  first  was  deemed  by  far 
the  best  method,  but  it  was  only  practicable  on  suitable  and  healthy 
roots.  Woofendale,  writing  of  this  operation  in  1783,  says:  "Another 
method  of  supplying  the  loss  of  teeth  by  art  is  by  fixing  the  crown  or 
enamelled  part  of  the  sound  human  tooth  to  the  root  of  a  tooth  of  which 
the  enamelled  part  is  wholly  decayed  or  broken.  This  is  done  by  filing 
each  properly,  and  uniting  them  by  the  assistance  of  a  screw  of  gold  or 
silver,  which  may  be  done  so  completely  that  it  is  sometimes  not  without 
difficulty  they  can  be  separated,  in  some  instances  for  several  years,, 
provided  the  orifice  in  the  root  of  the  tooth  through  which  the  nerve 
passes  is  not  much  decayed.  This  operation  can  only  be  performed 
where  the  teeth  have  but  one  root ;  neither  can  it  be  practised  when  the 
root  of  a  tooth  is  out." 

Human  teeth  were  also  fastened  in  the  mouth  by  tying  them  by 
ligatures  of  gold  or  silver  wire,  silk,  cotton  thread,  etc.  Human  teeth 
were  costly  and  scarce.  In  an  advertisement  inserted  in  a  Philadelphia 
paper  in  1784,  M.  Le  Mayeur,  a  dentist,  offers  two  guineas  each  for 
sound  teeth  to  be  obtained  from  "  persons  disposed  to  sell  their  front 
teeth  or  any  of  them." 

The  teeth  of  cattle  were  largely  used.  They  were  fastened  in  the 
mouth  by  the  same  means  as  human  teeth.  Their  color  was  light  and 
varied  but  little ;  the  pulp-chambers  Avere  very  large  in  proportion  to 
their  size,  which  so  weakened  the  teeth  that  they  were  liable  to  break 
during  mastication,  and  in  other  respects  they  seem  to  have  been 
unsatisfactory. 

Hippopotamus  ivory  was  probably  more  extensively  used  than  any 
other  of  the  dental  substitutes.     When  two  or  more  consecutive  teeth; 


210 


FORMATION  OF  BODIES  AND  ENAMELS.  211 

were  inserted  it  was  almost  the  only  material  in  use,  either  as  carved  in 
a  block  into  the  semblance  of  the  lost  natural  teeth  or  as  a  base  on  which 
to  secure  human  or  animal  teeth. 

Ivory  of  the  elephant  and  walrus  and  bone  were  used  for  tlie  cheaper 
grades  of  operations :  dentures  made  of  these  materials  were  in  every 
respect  unsatisfactory. 

Porcelain  teeth  were  not  introduced  into  this  country  until  1817. 
The  first  use  of  them  of  which  we  have  knowledge  was  by  A.  A.  Plan- 
tou,  a  Frenchman,  who  began  the  practice  of  dentistry  in  Philadelphia 
about  that  time.  He  commenced  the  manufacture  of  mineral  teeth 
about  1820,  and  received  for  them  a  certificate  of  approbation  from  the 
Medical  Society  of  Philadelphia. 

Charles  W.  Peale  in  1822  and  Samuel  W.  Stockton  in  1825  were  the 
next  after  Plantou  to  manufacture  porcelain  teeth  :  they  were  soon  fol- 
lowed by  a  host  of  other  experimenters,  and  by  the  year  1838  mineral 
teeth  had  come  into  general  use. 

The  form  and  color  of  the  teeth  made  about  this  time  very  imper- 
fectly represented  the  natural  organs,  and  the  material  of  which  they 
were  made  was  so  poorly  adapted  to  the  purpose  that  exposure  to  the 
high  temperature  necessary  to  soldering  caused  their  fracture.  But  about 
1838  great  improvements  were  made  by  Dr.  Elias  Wildman  of  Phila- 
delphia. He  produced  such  results  in  life-like  appearance  as  had  not 
been  obtained  before,  and  have  truly  been  said  to  have  remained  un- 
excelled to  the  present  time.  To  him  has  been  accorded  the  honor  of 
placing  the  manufacture  of  porcelain  teeth  on  a  scientific  basis. 

Materials  Used  in  the  Formation  of  Bodies   and  Enamels. 

These  are  feldspar,  silica,  and  kaolin  or  clay.  The  pigments  em- 
ployed to  imitate  the  various  shades  of  color  of  the  natural  enamel,  den- 
tine, and  gums  are  titanium  oxide,  platinum,  cobalt,  iron,  gold,  and  tin. 

The  body  represents  the  dentine  of  the  natural  tooth,  and  is  composed 
of  feldspar,  silica  (in  the  form  of  finely-ground  quartz),  and  kaolin  (clay), 
and  the  yellow-white  or  ivory-like  color  of  that  portion  of  a  tooth  is  im- 
parted to  it  by  the  addition  of  finely-ground  titanium  oxide. 

The  frits  are  crude  colors  composed  of  metallic  oxides,  such  as  those 
of  gold,  tin,  cobalt,  etc.,  ground  exceedingly  fine,  in  combination  with 
feldspar  and  certain  fluxes  which  will  hereafter  be  described.  These 
are  burned  in  a  suitable  crucible,  and  then  powdered  for  use  in  impart- 
ing tints  to  enamels. 

Enamels  are  composed  chiefly  of  feldspar,  to  which  is  added  suf- 
ficient quantities  of  the  different  frits  to  produce  as  nearly  as  possible 
the  colors  of  the  natural  teeth  and  gums.  Bodies  and  enamels  especially 
prepared  for  the  manufacture  of  porcelain  teeth  should  possess,  after 
burning,  translucency  and  natural  color,  together  with  strength  and  heat- 
conducting  qualities  to  a  degree  that  will  admit  of  soldering  without 
danger  of  fracture  from  unequal  expansion.  Translucency  and  the 
power  of  withstanding  high  temperature  in  soldering  depend  largely 
upon  the  feldspar  which  forms  four-fifths  of  the  bulk  of  the  body. 

Silica  is  next  in  importance  as  a  constituent  of  the  body  :  its  function 
is  to  add  density  and  the  strength  required  for  masticatory  purposes, 


•212  MOULDING   AND   CARVING  PORCELAIN  TEETH. 

and,  being  highly  infusible,  to  assist  in  retaining  the  teeth  in  shape  dur- 
ing the  burning  process.  Without  silica  the  teeth  when  near  the  fusing- 
point  would  evince  a  tendency  to  assume  the  spherical  form,  and  their 
lines  and  characteristic  features  would  be  lost. 

Kaolin  and  the  clays  in  general  give  plasticity  to  the  body,  by  which 
the  workman  is  enabled  to  mould  and  handle  the  unburned  teeth  and 
blocks  without  danger  of  breaking  them  :  it  also  imparts  strength  to  the 
porcelain  mixture. 

Feldspar — generally  spoken  of  as  a  double  silicate  of  aluminum  and 
potassium — is  represented  by  the  formula  AlgOg.KgO.GSiOa.  The  best 
quality  of  feldspar  is  found  in  the  neighborhood  of  Wilmington,  Del. 
It  possesses  a  distinct  cleavage,  and  when  broken  splits  into  plates  of 
more  or  less  magnitude.  It  is  of  an  indefinite  color,  between  yellow  and 
pink,  but  when  fused  in  the  furnace  it  becomes  transparent  and  color- 
less, and  if  not  exposed  to  a  too  prolonged  or  an  excessively  high  tem- 
perature it  retains  its  original  form  without  rounding  at  the  corners : 
this  is  one  of  the  tests  of  good  feldspar.  There  are  several  deposits  of 
this  mineral  in  Eastern  Pennsylvania  which,  though  beautiful  and  trans- 
parent in  appearance,  have  been  found  to  be  entirely  unfit  for  dental 
porcelain  on  account  of  their  opaque-white  appearance  when  fused  in 
the  furnace. 

Feldspar  from  different  parts  of  the  same  quarry  has  been  observed 
to  differ  in  quality.  In  selecting  spar  for  the  preparation  of  enamels  a 
number  of  pieces  broken  from  the  most  perfect-appearing  specimens 
should  be  fused  in  the  furnace  to  determine  the  quality.  The  crude 
pieces  from  which  the  samples  were  taken,  if  found  satisfactory,  are  then 
broken  into  small  fragments  with  a  steel  hammer  until  they  become  of  a 
size  to  admit  of  its  being  ground  in  a  large  Wedgwood  mortar;  at 
intervals  the  powder  is  sifted  through  a  No.  10  bolting-cloth  sieve, 
placed  in  covered  jars,  and  kept  dry  for  future  use. 

In  the  preparation  of  feldspar  for  enamels  the  grinding  should  not  be 
carried  too  far,  as  transparency  may  be  greatly  lessened,  or  even  entirely 
lost,  by  its  being  ground  too  fine.  The  effect  of  a  complete  obliteration 
of  the  crystallization  of  the  feldspar  by  too  much  grinding  may  be 
observed  in  a  test  suggested  by  Dr.  William  R.  Hall  in  the  chapter  on 
"  Moulding  and  Carving  Porcelain  Teeth,"  American  System  of  Dentis- 
try :  It  consists  in  placing  on  a  slide  covered  with  coarse  silex  a  small 
piece  of  crude  feldspar  of  the  best  quality  ;  then  taking  another  piece 
from  the  same  specimen,  grinding  it  very  fine,  and  fusing  the  two  in 
the  furnace  ;  and  when  cold  the  difference  in  appearance  will  demonstrate 
that  when  ground  into  a  very  fine  powder  loss  of  transparency  is  appa- 
rent, and  that  to  preserve  its  beauty  feldspar  must  be  ground  only  to  a 
certain  fineness,  beyond  which  opacity  is  the  result. 

In  preparing  feldspar  in  large  quantities  for  extensive  use  by  the 
manufacturers  of  moulded  teeth  it  is  customary  to  calcine  the  spar  by 
lieating  to  redness,  and  dropping  it  into  water  while  hot.  This  is  done 
to  facilitate  the  reduction  of  the  large  masses  into  small  fragments  suit- 
able for  grinding  in  the  mortar,  which  in  the  large  factories  consists  of  a 
tub  with  a  burr-stone  or  quartz  bottom.  The  pestle,  which  is  generally 
formed  of  a  piece  of  the  same  mineral,  is  arranged  to  revolve  by  machi- 
nery.    The  grinding  is   done    under  water.     While  this  plan   is  less 


FORMATION  OF  BODIES  AND  ENAMELS.  213 

laborious  than  dry  grinding,  it  probably  never  aifords  as  good  results, 
in  consequence  of  the  excessive  fineness  of  the  powdered  spar. 

Silioa  (SiOa). — This  body,  sometimes  called  quartz,  occurs  in  crystal- 
line and  amorphous  forms  :  it  is  colorless,  infusible  at  ordinary  tempera- 
tures, insoluble  in  water  and  in  all  the  acids  except  hydrofluoric.  The 
amorphous  and  gelatinous  varieties  are  partially  soluble  in  alkaline  car- 
bonates, but  quite  soluble  in  caustic  alkalies.  Silica  combines  with  the 
bases  to  form  silicates. 

The  purest  natural  form  of  silica  is  the  transparent  and  colorless 
variety  of  quartz  known  as  rock-crystal,  which  is  of  frequent  occurrence 
in  beautiful  six-sided  prisms  terminated  by  six-sided  pyramids,  easily 
distinguished  by  their  great  hardness.  Without  transparency  and  crys- 
talline structure  silica  is  met  with  in  the  form  of  chalcedony  and  carne- 
lian,  agate,  cat's-eye,  onyx,  opal,  and  other  precious  stones.  Sand,  of 
which  the  whiter  varieties  are  pure  silica,  appears  to  have  been  formed 
by  the  disintegration  of  silicious  rocks,  and  has  generally  a  yellow  or 
brown  color,  due  to  the  presence  of  oxide  of  iron. 

Flints,  which  are  generally  found  in  chalk  formations,  are  specimens 
of  the  hardest  variety  of  silica,  offering  greater  resistance  than  quartz  to 
impressions  of  all  kinds.  Flint  is  opaque  and  of  a  dull-brown  color, 
which  is  due  to  impurities. 

A  variety  of  quartz  well  suited  for  use  in  the  manufacture  of  porce- 
lain teeth  is  found  in  great  abundance  in  Pennsylvania  and  other  parts 
of  the  United  States.  It  occurs  in  large  irregular  masses,  white  in  color, 
and  very  difficult  to  powder.  It  is  used  for  the  purpose  of  giving 
stability  and  firmness  to  porcelains,  and  its  infusibility  stiffens  and  keeps 
the  other  materials  in  shape,  so  that  an  object  made  of  porcelain  may 
preserve  its  moulded  form  while  exposed  to  the  high  temperature  dur- 
ing the  fusing  process.  For  these  reasons  it  is  incorporated  with  feld- 
spar and  clay,  and  is  looked  upon  as  the  "  main  prop  in  tooth-body,"  in 
which  it  is  just  as  essential  for  the  purpose  of  lessening  fusibility,  as  flux 
is  essential  in  enamels,  which  are  required  to  fuse  more  readily. 

Quartz  must  be  ground  under  water  to  an  impalpable  powder.  The 
proper  degree  of  fineness  may  be  ascertained  by  placing  a  small  portion 
of  the  powdered  quartz  on  the  end  of  the  tongue  :  if  it  is  found  to  be 
without  grittiness  when  rubbed  against  the  teeth,  it  may  be  dried  for  use. 

The  preliminary  steps  in  the  reduction  of  this  hard  mineral  to  a  fine 
state  of  division  consists  in  heating  to  a  bright  redness  as  large  pieces  as 
the  muffle  of  a  furnace  will  admit,  and  dropping  them  into  cold  water  : 
this  causes  the  quartz  to  crumble  into  pieces  of  the  size  of  a  pea,  which 
are  further  reduced  in  a  Wedgwood  mortar  by  the  successive  blows  of 
a  heavy  pestle  until  fine  enough  to  pass  through  a  No.  10  bolting-cloth 
sieve,  after  which  it  may  be  brought  to  the  state  of  an  impalpable  pow- 
der by  grinding  with  water  either  in  an  ordinary  hard  porcelain  mortar, 
or,  when  it  is  prepared  in  very  large  quantities,  by  one  of  the  powerful 
grinding-mills,  turned  by  steam,  in  use  at  the  large  manufactories. 

Clay  is  a  hydrated  silicate  of  alumina,  and  when  pure  may  be  repre- 
sented by  the  formula  (2A1.303,3Si02)  +  Slip.  It  is  formed  by  the 
long-continued  action  of  air  and  water  upon  granite  rock,  the  disinte- 
gration of  which  is  probably  due  to  both  mechanical  and  chemical 
causes.     Mechanically,  the  rock  is  continually  broken  down  by  variations 


214  MOULDING  AND   CARVING   PORCELAIN  TEETH. 

of  temperature  and  by  the  congelation  of  water  within  its  minute  pores. 
Chemically,  the  action  of  water  containing  carbonic  acid  tends  to 
remove  the  potash  from  the  feldspar  and  mica  in  the  form  of  carbonate 
of  potash,  whilst  the  silicate  of  alumina  and  the  quartz  are  separated 
by  the  action  of  the  water :  the  former,  being  the  lighter,  is  separated 
from  the  heavy  quartz,  and,  when  again  deposited,  constitutes  clay. 

Kaolin  is  a  pure  quality  of  clay  from  which  such  impurities  as  sand 
and  mica  have  been  carefully  excluded  by  washing,  which  is  accomplished 
by  mixing  the  clay  with  a  large  amount  of  water  in  a  basin-shaped  ves- 
sel. It  is  at  first  thoroughly  stirred,  and  then,  after  sufficient  time  has 
been  allowed  for  the  sand  to  settle,  the  upper  or  lighter  layer  is  poured 
or  run  off  into  another  vessel.  It  is  then  permitted  to  stand  until  the 
kaolin  subsides  to  the  bottom  of  the  vessel  :  the  water  is  siphoned  off; 
the  kaolin  is  then  dried,  when  the  mass  may  be  turned  out  and  the  bot- 
tom scraped  free  from  any  sand  found  adhering  to  it. 

Clay  is  infusible  in  an  ordinary  furnace  when  heated  alone,  but 
readily  unites  with  feldspar,  at  high  temperature,  when  incorporated  with 
it,  and  is  an  element  of  strength  in  porcelain  compounds. 

Kaolin  should  be  thoroughly  mixed  with  the  other  ingredients  of  the 
body  while  in  the  dry  state,  and  complete  admixtures  may  be  attained  by 
passing  the  dry  body  through  a  No.  9  bolting-cloth  sieve. 

German  clay  is  imported  from  Europe,  and  is  used  to  manufacture 
various  articles  which  require  an  infusible  silicate  of  aluminum. 

Formulas  for  Body. 

The  different  materials  entering  into  the  composition  of  bodies 
should  be  kept  in  a  dry  state  in  labelled  jars,  and  the  weighing  of  each 
before  mixing  should  be  done  with  precision.  The  following  formulas 
of  well-tested  standard  bodies  for  moulded  block  teeth  are  given  by 
Dr.  Wm.  R.  Hall  -} 

Bodies  for  Moulded  Block  Teeth. 


I. 

Kaolin 1  oz. 

Silica 3   " 

Feldspar 18    " 

Titanium  oxide 65  gr. 

Starch,  10  gr.  to  each  oz. 


II. 

German  clay j  oz. 

Silica 3  " 

Feldspar 18  " 

Titanium  oxide 65  gr. 

Starch,  10  gr.  to  each  oz. 


It  was  formerly  the  custom  of  makers  of  moulded  teeth  to  at  first 
partially  burn  or  biscuit-bake  the  teeth  or  blocks.  The  addition  of 
starch  to  the  body  does  away  with  the  necessity  of  the  "  first  burning," 
as  it  gives  the  teeth  sufficient  firmness  to  allow  of  their  being  safely 
handled  during  the  process  of  trimming,  which  must  be  done  before  the 
final  burning.  The  titanium  oxide  and  the  starch  are  placed  in  a  mortar 
and  ground,  at  first  without  water;  kaolin  and  silica  are  then  added, 
ground  together,  and  sifted  through  a  No.  9  bolting-cloth  sieve  :  the 
feldspar  is  then  added,  and  after  sieving  a  second  time  the  mixture  is 
ready  for  use,  and  should  be  kept  in  a  covered  glass  jar.  As  it  is  often 
desirable  to  have  in  stock  a  small  variety  of  bodies  of  different  shades, 
it  will  be  found  of  great  convenience  to  have  attached  to  each  jar  a  test 
^  American  System  of  DentiMry,  p.  962. 


COLORS  USED  IN  THE  MANUFACTURE  OF  PORCELAIN  TEETH.    215 

sample  of  the  body,  which  has  been  burned  in  the  furnace,  so  that  color 
and  texture  may  be  ascertained  without  loss  of  time. 

In  preparing  bodies  and  enamels  for  use  in  moulds  they  are  mixed 
with  water,  and  then  dried  to  the  consistence  of  dough,  when  they  are 
placed  in  the  moulds  with  small  spatulas.  The  enamels  being  laid  in  the 
face  side  and  the  body  in  the  pin  side  of  the  moulds,  these  two  halves  of 
the  mould  are  then  adjusted  to  each  other,  placed  in  a  strong  press  until 
in  complete  contact,  secured  by  a  strong  clamp,  and  exposed  to  a  heat 
sufficient  to  bake  the  starch,  which  so  hardens  the  teeth  or  blocks  that 
they  will  withstand  a  very  considerable  amount  of  force  without  danger 
of  breaking.  During  the  burning  of  the  teeth  the  starch  burns  out 
without  injury  to  either  the  body  or  enamels. 

In  bodies  used  for  carved  blocks  no  starch  need  be  used.  The  work 
being  done  entirely  by  hand  with  small  knives,  it  is  essential  that  the 
material  should  be  plastic  enough  to  cut  with  facility,  while  it  possesses 
sufficient  toughness  to  permit  of  careful  handling.  These  conditions 
are  obtained  by  simply  mixing  the  body  with  water,  the  kaolin  present 
furnishing  the  desired  plasticity. 

Bodies  for  Carved  Blooks. 

Dr.  William  R.  Hall's  formulas  : 

No.  1.  No.  2. 

Kaolin 1  oz, 

Silica 3J   " 

Feldspar 14   " 

Titanium  oxide 40  gr, 


German  clay J  oz. 

Silica 3^  " 

Feldspar 14     " 

Titanium  oxide 40     " 


Formulas  of  Professor  Wildman  : 

No.  1.  No 

Feldspar 4  oz, 


Silica 320  gr. 

Kaolin  (Massey's) 120   "' 

Titanium  oxide 4  to  8   " 


Feldspar  (Delaware) 3  oz. 

Feldspar  (Wissahickon)    ....  1    " 

Kaolin  (Hoopes') 40  gr. 

Kaolin  (Massey's) 80   " 

Silica 360  " 

Titanium 4  to  8   " 


These  bodies  are  of  medium  color :  they  may  be  made  darker  or 
lighter  by  varying  the  quantity  of  titanium  oxide.  Iron  or  steel  spat- 
ulas should  not  be  used  in  mixing  bodies :  bone  or  ivory  mixers  may  be 
used  without  fear  of  contaminating  the  material. 

Colors  used  in  the  Manufacture  op  Porcelain  Teeth. 

The  colors  used  in  imitating  the  tints  of  the  natural  enamel,  dentine, 
and  gums  are  produced  by  thoroughly  incorporating  titanium  oxide  and 
preparations  of  gold,  tin,  platinum,  iron,  and  cobalt  with  the  mineral 
substances  of  which  porcelain  bodies  and  enamels  are  composed. 

The  texture  and  coloring  of  porcelain  teeth  have  reached  a  high 
state  of  perfection  in  the  United  States  and  England.  The  making  and 
application  of  bodies  and  enamels,  while  requiring  much  skill  and  expe- 
rience, are  undoubtedly  greatly  in  advance  of  forms  and  sizes.  In  the 
direction  of  colors  and  texture  we  have  probably  all  that  could  be 
desired.    And  the  fact  that  artificial  teeth  have  not  reached  a  sufficiently 


216 


MOULDING  AND   CARVING  PORCELAIN  TEETH. 


high  standard  of  artistic  perfection  to  enable  them  to  imitate  the  natural 
organs  closely  enough  to  defy  detection,  is  certainly  not  due  to  any 
deficiency  in  the  materials  of  which  they  are  made,  but  to  other  causes 
which  will  be  considered  hereafter. 

Color  frits  are  made  by  grinding  the  metal  or  its  oxide  with  feldspar 
and  a  fine  quality  of  glass,  which  serves  as  a  flux  to  lower  the  fusibility 
of  the  enamel.  The  levigation  is  continued  until  a  very  fine  state  of 
division  is  reached,  after  which  they  are  biscuit-burned  in  the  mufl&e  of 
a  furnace,  or  they  may  be  securely  packed  in  a  white-clay  crucible,  pro- 
vided with  a  perfectly  secure  top,  and  burned  in  any  ordinary  stove  or 
furnace  in  which  a  high  enough  temperature  can  be  obtained.  When 
cool  the  frit  is  removed  and  pulverized  in  a  Wedgwood  mortar,  which 
has  first  been  thoroughly  scoured  out  by  grinding  with  coarse  silica  to 
effectually  remove  traces  of  any  coloring  j)ignient  previously  prepared  in 
the  same  mortar. 

In  grinding  prepared  platinum  or  gold-foil  the  feldspar  and  flux  are 
added  by  small  portions  at  a  time  until  the  greatest  degree  of  fineness 
is  attained.  The  shade  of  the  enamel  will  depend  largely  upon  the 
state  of  minute  division  of  the  metal  or  oxide.  As  an  example  it  may 
be  stated  that  distinctly  different  shades  may  be  made  from  portions  of 
the  same  mixture  by  reducing  one  lot  to  extreme  fineness  and  leaving 
the  other  comparatively  coarse. 


Blue  Frits. 


Wm.  R.  Hall's  formulas 


Platinum  Frit,  Blue. 

Platinum  (dissolved  in  aqua  regia)     1  dwt. 

Feldspar 1  oz. 

Plate  glass 20  gr. 


Platinum  Frit,  Gray. 

Platinum  frit 30  gr. 

Titanium  oxide 10  " 

Gold  frit 100  " 


Cobalt  Frit,  Azure  Blue. 

Smalt  (cobalt) 60  gr. 

Titanium  oxide 6  " 

Gold  frit 60  " 

Feldspar 1  oz. 


Iron  Frit,  Gray. 

Iron  scale 4  gr. 

Titanium  oxide 1   " 

Gold  frit 60   " 

Feldspar 1  oz. 


Gold  Frit,  Reddish-brown. 

Pure  gold-foil .    .  12  gr. 

Plate  glass 20   " 

Feldspar 1  oz. 


Dr.  Wm.  R.  Hall's  directions  for  preparing  the  platinum  and  gold  frits 
are  as  follows  :  "  The  metal  for  the  platinum  frit  is  dissolved  in  boiling 
nitro-muriatic  acid,  care  being  taken  not  to  use  more  acid  than  is  just 
sufficient  to  make  a  saturated  solution.  When  cold  the  spar  and  glass 
are  added  and  mixed  with  a  glass  rod,  and  placed  in  a  clay  crucible  pre- 
viously washed  inside  with  powdered  quartz  mixed  with  water.  A  cover 
must  be  closely  fitted  to  the  inner  edges  of  the  crucible,  the  joint  being 
carefully  closed  or  luted  with  clay  and  quartz,  and  burned  as  has  been 
described. 

"  The  metal  of  the  gold  frit  is  dissolved  in  cold  nitro-hydrochloric 


COLORS  USED  IN  THE  MANUFACTURE  OF  PORCELAIN  TEETH.    217 

acid  :  with  this  exception  it  is  treated  in  the  same  way  as  in  the  directions 
for  the  platinum  frit." 

Professor  Wildman,  who  called  the  gold  frit  "  silicate  of  gold," 
directed  that  "coarse  feldspar  120  gr.,  gold-foil  10  gr.,  flux  8  gr.  be 
placed  in  a  mortar  and  ground  until  the  gold  is  entirely  cut  up :  it  is 
then  made  into  a  ball,  placed  on  a  slide,  and  fused  in  the  mufi&e ;  then 
made  fine,  ready  for  use."  His  "  gold  mixture  "  was  made  by  dissolving 
8  grains  of  gold-foil  in  aqua  regia,  to  which  were  added  and  well  stirred 
300  grains  of  very  finely  pulverized  feldspar.  When  nearly  dry  the 
mixture  was  formed  into  a  ball  and  fused  on  a  slide  in  the  muffle  of  the 
furnace,  after  which  it  was  pulverized  and  kept  dry  for  use. 


Professor  Wildman's  Formulas  for  Point  and  Base  Enamels. 


No.  l,for  Points  {gray). 

Feldspar 1  oz. 

Silicate  of  gold 6  gr. 

Prep,  sponge  platinum 4   " 

Flux 20   " 


No.  2,  Neck  or  Base  (yellow). 

Feldspar 1  oz. 

Titanium  oxide 8  gr. 

Prep,  sponge  platinum 4   " 

Flux 24   " 


No.  3,  Yellow. 

Feldspar 1  oz. 

Titanium  oxide 8  gr. 

Prep,  sponge  platinum      4  " 

Gold  mixture 25  " 

Flux 24  " 


No.  4,  Gray. 

Feldspar 1    oz. 

Titanium  oxide IJ  gr- 

Prep.  sponge  platinum 4     " 

Light  cobalt  ashes 4     " 

Flux 24    " 


No.  5,  Blue. 

Feldspar 1 

Sponge  platinum       3 

Light  cobalt  ashes 2-3 

Flux 24 


gr. 


The  enamels  of  Professor  Wildman  were  more  fusible  than  those  of 
William  R.  Hall,  and  were  probably  not  as  well  adapted  for  moulding 
and  general  manufacturing  purposes  as  were  those  of  the  latter,  though 
in  translucency,  texture,  and  color  they  were  unsurpassed. 

The  making  of  bodies  and  enamels  and  their  application  require  both 
skill  and  experience.  There  should  also  be  a  correct  relation  of  fusing- 
points  between  bodies  and  enamels.  As  the  fusibility  of  the  bodies  of 
Hall  and  Wildman  probably  differ,  it  would  not  do  to  use  the  enamels 
of  one  with  the  bodies  of  the  other. 

In  preparing  coloring  frits  it  should  be  borne  in  mind  that  a  too 
high  or  long-continued  heat  may  reduce  the  oxides  to  a  metallic  state, 
and  thus  ruin  them  for  use  as  coloring  pigments.  The  burning  should 
either  be  done  in  the  muffle  of  the  furnace  or  in  a  white-clay  crucible 
provided  with  a  top  securely  luted  in  and  made  perfectly  tight  with  a 
mixture  of  silica  and  kaolin,  for  the  purpose  of  protecting  the  frit  from 
the  action  of  the  fuel-gases.  The  burning  should  be  done  at  a  tempera- 
ture sufficiently  high  to  glaze  the  frit,  and  the  crucible  need  not  be 
placed  in  the  furnace  until  that  point  has  been  nearly  attained,  other- 
wise it  might  deteriorate  in  its  color-giving  qualities  by  too  long  ex- 
posure to  heat. 


218  MOULDING  AND   CARVING  PORCELAIN  TEETH. 

Directions  foe  Making  Professor  Wildman's  Enamels. 

Prof.  Wildman  seemed  to  have  preferred  the  dry  method  of  making 
colors.  The  "  prepared  platinum  "  which  he  used  in  point  enamels  was 
made  by  grinding  1  part  of  sponge  platinum  with  15  parts  of  feldspar. 
In  compounding  No.  1  point  enamel  he  directed  that  the  "  prepared 
platinum "  be  ground  alone  until  extreme  fineness  be  reached,  after 
which  the  silicate  of  gold  and  flux  are  to  be  added,  and  thoroughly 
ground  until  reduced  to  the  fineness  of  the  platinum.  There  is  no  dan- 
ger of  getting  these  coloring  pigments  too  fine ;  but  with  the  feldspar, 
which  is  next  to  be  added,  the  case  is  different :  it  is  added  a  little  at  a 
time  until  thoroughly  incorporated  with  the  platinum  and  gold  mixtures 
and  the  flux  ;  but  the  spar  must  not  be  ground  too  fine,  or  its  "  life  and 
beauty  will  be  lost  and  we  shall  have  a  glassy  enamel."  The  manner  in 
which  Dr.  Wildman  ascertained  the  correct  degree  of  fineness  of  the 
enamel  after  the  spar  was  added  was  "  to  take  a  little  of  the  enamel  out 
of  the  mortar,  mix  it  with  water,  and  apply  to  a  piece  of  biscuited  body ; 
when  nearly  dry,  cut  a  few  indentations  in  it,  and  pass  the  finger  lightly 
over  it ;  if  it  rubs  perfectly  smooth,  it  is  fine  enough  for  use." 

No.  2  base  or  yellow  enamel  was  prepared  by  first  grinding  the 
titanium  and  platinum  together,  the  shade  of  this  enamel  depending  very 
much  upon  a  state  of  minute  division  of  these  colors.  If  the  platinum 
is  brought  to  a  greater  state  of  fineness  than  the  titanium,  the  latter  will 
be  masked,  and  the  resulting  color  will  be  of  a  greenish  tint ;  but  when 
the  degree  of  fineness  of  the  two  pigments  is  equal,  the  yellow  imparted 
by  the  titanium  is  merely  softened  or  toned  by  the  platinum,  and  a  color 
is  produced  which  admirably  imitates  the  shade  of  the  base  of  a  healthy 
natural  tooth.  By  grinding  either  of  these  colors  separately  to  a  state 
of  extreme  fineness,  and  then  adding  the  other,  which  has  not  been 
brought  to  so  high  a  state  of  minute  division,  the  finer  color  will  be 
found  to  predominate,  shaded  only  by  the  coarser  one.  The  flux  is 
next  added,  and,  as  coarse  particles  of  this  material  are  liable  to  pro- 
duce small  air-bubbles  in  the  surface  of  the  enamel,  it  must  also  be 
ground  very  fine.  The  spar  is  now  added  a  little  at  a  time,  as  in  No.  1 
enamel. 

In  making  No.  3  enamels  the  procedure  is  precisely  the  same  as  in 
Nos.  1  and  2,  with  the  exception  of  the  addition  of  the  gold  mixture, 
which  yields  a  brownish  tint,  the  depth  of  shade  being  governed  by  the 
quantity  used.  When  it  is  desired  to  but  slightly  shade  the  yellow  a 
smaller  amount  of  the  gold  mixture  may  be  added. 

Nos.  4  and  5,  gray  and  blue  enamels,  are  prepared  as  directed  in 
making  the  preceding  numbers,  with  the  addition  of  the  "  light  cobalt- 
ashes,"  2  grains  of  which  produces  a  light-blue  shade,  and  3  grains  when 
the  blue  is  required  to  predominate. 


Dr.  William  E.  Hall's  Formulas  for  Enamels. 

It  will  be  observed  that  the  enamels  of  Dr.  Hall  have  no  flux  as  an 
ingredient  other  than  that  which  is  contained  in  the  different  frits.  In 
this  respect  they  differ  materially  from  the  formulas  of  Prof.  Wildman. 
On  the  ground  that  fluxes  give  a  glassy  surface  to  the  finished  teeth 


COLORS  USED  IN  THE  MANUFACTURE  OF  PORCELAIN  TEETH.    219 


and  decrease  the  beauty  of  good  spar,  Dr.  Hall  asserts  that  none  should 
be  used  in  enamels. 


Platinum-gray,  No.  1. 
tt.-gray  frit  .    .    .    .    1 


Plat.-gray 
Feldspar 
Starch  . 


1  gr. 

1  oz. 

15  gr. 


No.  2. 


Plat.-gray  frit      .    .    .    2  gr. 

Feldspar 1  oz. 

Starch 15  gr. 

Platinum-gray,  No.  4- 

Plat.-gray  frit  .    .    .    .    4  gr. 

Feldspar 1  oz. 

Starch 15  gr. 

Oold-yellow,  No.  1. 

Titanium,  pure   .    .    .    1  gr. 

Gold  frit 2  " 

Starch 15  " 

Feldspar 1  oz. 


Platinum-blue,  No.  1. 

Plat.-blue  frit  ....    1 

Feldspar 1 

Starch 15 

No.  3. 

Plat.-blue  frit  ....    3 

Feldspar 1 

Starch   .......  15 

Platinum-blue,  No.  5. 

Plat.-blue  frit  ....    5 

Feldspar 1 

Starch  .......  15 

Gold-yellow,  No.  2. 

Titanium,  pure    ...    2 

Gold  frit 4 

Starch 15 

Feldspar 1 


gr- 


gr. 


Iron-gray,  No.  4- 


Iron -gray  frit  .  . 
Feldspar  .  .  .  . 
Starch 

No.  6. 

Iron-gray  frit  .  . 
Feldspar  .  .  .  . 
Starch  


4gr. 

1  oz. 

15  gr. 


6gr. 

1  oz. 

15  gr. 


Iron-gray,  No.  8. 


Iron-gray  frit 
Feldspar  .    . 
Starch   .    .    . 


8gr. 
1  oz. 
15  gr. 


Gold-yellow,  No.  3. 


Titanium,  pure 
Gold  frit  .  .  . 
Starch  .... 
Feldspar  .    .    . 


Brown-yellow,  No.  1. 


Titanium,  pure 
Platinum  frit  . 
Gum  frit  .  .  . 
Feldspar  .  .  . 
Starch     .    .    .    . 


1  gr. 
1  ■" 
4  " 
1  oz. 
15  gr. 


Rroivn-yellow,  No.  2. 


Titanium, 
Platinum 
Gum  frit 
Feldspar 
Starch     . 


pure 
frit     . 


3gr. 
6  " 
15  " 
1  oz. 


2gr. 
2  " 
8  " 
1  oz. 
15  gr. 


The  tint  of  enamels  is  more  or  less  influenced  by  the  quality  of  the 
feldspar,  some  varieties  imparting  a  blue  and  some  a  white  or  slightly 
yellow  tint.  A  feldspar  from  Marcus  Hook  in  Delaware  county,  Penn- 
sylvania, has  been  found  to  afford  a  beautiful  white  enamel,  which 
answers  admirably  for  teeth  suitable  for  persons  of  the  lymphatic  tem- 
perament— a  type  which  requires  little  or  no  color. 

Cobalt,  which  has  been  mentioned  as  one  of  the  occasional  coloring 
ingredients  in  enamels,  is  what  is  known  in  commerce  as  "  smalt."  It  is 
sometimes  used  in  producing  the  brighter  shades  of  blue.  It  is  not,  how- 
ever, a  permanent  color,  and  it  requires  to  be  associated  with  some  other 
oolor,  such  as  platinum,  to  prevent  it  from  being  lost  during  the  burning 
•of  the  teeth. 

Dr.  Hall  objects  to  the  use  of  sponge  platinum  in  the  formation  of 
platinum  frit,  on  the  ground  that  it  is  more  expensive  and  requires  much 
lieavy  grinding  to  cut  it  sufficiently  fine  to  make  good  frit,  his  preference 
being  for  the  method  in  which  the  metal  is  dissolved  in  nitro-hydro- 
ohloric  acid,  as  described  on  page  216. 

Sponge  platinum  is  made  by  dissolving  pure  platinum  filings  or 
scraps  in  six  times  their  weight  of  nitro-hydrochloric  acid  composed  of 
1  part  of  nitric  to  3  parts  of  hydrochloric.  The  platinum  and  mixed 
acid  should  be  placed  in  a  clean  Florence  flask  and  heat  gently  applied 
by  means  of  a  sand-bath,  for  the  purpose  of  facilitating  the  action  of  the 


220  MOULDING  AND  CARVING  PORCELAIN  TEETH. 

acid  on  the  metal.  The  heat  should  not  be  too  great,  otherwise  the 
effervescence  will  be  so  violent  that  a  portion  of  the  mixture  may  be 
ejected  from  the  flask.  Should  effervescence  cease  entirely  before  all  the 
metal  is  dissolved,  the  fluid  must  be  decanted  and  more  acid  added  until 
the  last  particle  of  the  platinum  disappears.  The  solution  is  then  poured 
into  an  evaporating  dish  and  evaporated  on  the  sand-bath  until  the  mass 
is  nearly  dry  and  the  resulting  salt  assumes  the  crystalline  form.  At  this 
part  of  the  operation  care  must  be  taken  that  the  temperature  of  the 
sand-bath  is  kept  below  450°  F. ;  above  that  point  decomposition  of  the 
platinic  chloride  takes  place,  when  a  portion  of  the  chlorine  is  driven  off^ 
causing  a  precipitate  of  platinous  chloride,  wdiich  is  of  a  greenish-gray 
color  and  insoluble  in  water.  If,  however,  no  such  accident  occurs,  the 
platinic  chloride  will  be  of  a  reddish-brown  color,  very  deliquescent  and 
freely  soluble  in  water.  The  crystallized  salt  is  dissolved  in  pure  dis- 
tilled water,  and  allowed  to  stand  until  it  becomes  perfectly  clear,  when 
it  is  to  be  filtered,  after  which  a  cold  saturated  solution  of  ammonium 
chloride  (sal  ammoniac)  is  gradually  added  to  the  platinic  chloride  until 
all  precipitation  ceases.  When  the  precipitate  has  entirely  settled  it  is 
collected  by  pouring  off  the  liquid,  thoroughly  washing  the  spongy  metal, 
drying,  and  placing  away  for  future  use  in  small  glass  jars. 

Iron  scale  when  combined  with  spar  makes  an  exceedingly  natural 
blue-gray  color,  suitable,  when  toned  by  combination  with  other  frits,  aa 
designated  in  the  formula  on  p.  219,  for  the  cutting  edges  of  the  teeth  of 
young    persons. 

The  Application  of  Enamels. 

In  the  formulas  of  Professor  Wildman,  when  the  enamels  are  to  be 
used  on  body  No.  1,  30  grains  of  flux  must  be  added  to  the  former, 
instead  of  24,  as  given  in  the  formula.  Enamel  No.  1  is  intended  for 
shading  the  points  or  cutting  edges  of  the  teeth.  It  is  to  be  applied  to 
the  face  of  the  tooth,  much  thicker  at  the  point  than  at  the  base,  and  it 
must  extend  somewhat  beyond  the  body  in  order  to  imitate  the  trans- 
lucency  of  that  portion  of  the  teeth  of  young  adults,  but  if  the  enamel 
has  been  ground  too  fine,  it  will  be  impossible  to  obtain  this  appearance. 

No.  2  enamel  is  for  shading  the  base  of  the  tooth.  It  should  be  ap- 
plied first  and  laid  on  thick  at  the  base  or  neck,  becoming  thinner  and 
terminating  near  the  cutting  edge.  No.  1,  being  laid  on  after  No.  2, 
must  partially  cover  it,  so  that  they  will  not  terminate  too  abruptly  and 
thus  present  a  line  of  demarkation  between  the  two  colors. 

Enamel  No.  3  is  also  used  for  shading  the  base  or  neck  :  it  has  a 
browner  hue  than  No.  2,  and  in  many  cases  is  preferable  to  it,  on  ac- 
count of  the  yellow  being  softened  and  toned  by  the  gold  mixture. 

Enamel  No.  4,  used  on  a  yellow  body,  is  a  good  color  with  which  to 
imitate  the  teeth  of  elderly  people. 

Enamel  No.  5,  when  applied  on  a  light  body  as  a  point  enamel,  affords 
a  clear  bluish  appearance  which  is  very  desirable  in  some  cases.  A  very 
good  color  may  be  produced  in  imitation  of  the  teeth  of  elderly  persons 
by  first  applying  on  a  yellow  body  a  thin  coating  of  enamel  No.  3  over 
the  whole  tooth,  and  then  commencing  as  usual  by  applying  the  point 
enamel,  and  adding  No.  3  base  enamel  to  the  neck  of  the  tooth.     The 


GUM  FRIT.  221 

underlying  color,  showing  through,  gives  the  whole  tooth  a  grayish  shade. 
Enamels  are  to  be  ground  dry  and  kept  so,  and  are  to  be  mixed  with 
clean  water  only  at  the  moment  of  their  application. 

From  the  few  colors  given  by  Professor  Wildman  an  almost  endless 
variety  of  tints  may  be  obtained  by  alterations  in  the  shades  of  the 
bodies,  by  making  the  coloring  pigments  of  the  enamels  of  different 
degrees  of  fineness,  and  by  laying  on  the  enamels  in  different  degrees  of 
thickness. 

In  the  preparation  of  enamels  care  must  be  taken  to  select  only  good 
feldspar,  and,  above  all,  to  avoid  grinding  it  too  fine,  the  latter  being  the 
cause  of  the  loss  of  translucency,  and  indeed  of  all  the  desirable  qualities 
of  an  enamel. 

Gum  Fbit  (Purple  of  Oassius). 

The  dry  method  ^  is  the  one  now  employed  by  manufacturers  of 
porcelain  teeth  in  the  preparation  of  purple  of  Cassius,  the  coloring  pig- 
ment in  gum  enamel.  Pure  silver  240  gr.,  pure  gold  24  gr.,  and  pure 
tin  17|-  gr.  are  placed  in  a  crucible,  with  sufficient  borax  to  cover  the 
mass,  and  melted.  In  order  to  ensure  a  thorough  mixture  of  the  dif- 
ferent metals  the  melted  mass  should  be  poured  from  a  height  into  a 
vessel  of  cold  water,  and  this  process  of  granulation  should  be  repeated 
at  least  three  times  ;  but  at  every  melting  the  alloy  should  be  well  cov- 
ered with  borax  to  prevent  loss  of  the  tin  by  oxidation.  The  vessel 
into  which  the  molten  mass  is  poured  should  not  be  a  metallic  one. 

The  component  parts  of  the  alloy  having  now  been  thoroughly 
incorporated,  the  next  step  is  to  collect  the  granulated  mass  and  sepa- 
rate from  it  any  adherent  particles  of  glass  or  borax.  The  metal  is 
then  put  into  a  glass  or  porcelain  evaporating-dish  (the  Berlin  porcelain 
is  the  best),  and  sufficient  chemically  pure  nitric  acid  is  added  to  cover 
the  metal.  The  dish  is  now  placed  over  a  sand-bath,  and  gentle  heat 
applied  and  continued  until  chemical  action  ceases.  If  at  this  point  it 
is  found  that  all  the  metallic  particles  are  dissolved,  the  dish  may  be 
removed  from  the  bath.  Should  any  solid  particles  be  found  in  the 
solution,  a  little  more  nitric  acid  must  be  added  and  the  operation  con- 
tinued until  all  are  dissolved.  The  silver  having  been  entirely  dissolved 
by  the  nitric  acid,  the  solution  should  be  poured  off  and  the  remaining 
oxide  carefully  washed  until  the  last  trace  of  silver  is  removed.  After 
several  washings  with  a  large  quantity  of  pure  warm  water  the  latter 
should  finally  be  tested  with  a  clear  solution  of  common  salt,  and  if  it 
remains  clear,  without  show  of  milkiness,  the  silver  is  all  removed. 
When  the  oxide  is  sufficiently  washed  the  purple  of  Cassius  should  be 
dried  by  gently  heating,  after  which  it  is  ready  to  be  incorporated  with 
the  silicious  materials. 

The  process  of  making  gum-enamel  is  divided  into  three  stages  : 
First,  the  preparation  of  the  oxide  ;  second,  fritting,  or  by  the  aid  of 
heat  uniting  the  metallic  oxide  with  the  silicious  base ;  and  third, 
diluting  the  frit  so  as  to  form  the  desired  shade.     The  frit  is  formed 

^  The  dry  method  of  preparing  purple  of  Cassius  and  the  process  of  manufacturing 
the  gum-enamel  were  imparted  to  the  author  by  the  late  Professor  Wildman,  who  orig.- 
inated  it,  and  to  whom  is  due  the  credit  of  having  brought  the  preparation  of  bodies  and 
enamels  to  their  present  high  state  of  excellence. 


222  MOULDING  AND  CARVING  PORCELAIN  TEETH. 

by  mixing  8  grains  of  the  metallic  oxide  (purple  of  Cassius)  with  700 
grains  of  feldspar  and  175  grains  of  a  flux  compound  of  pure  quartz 
4  oz.,  glass  of  borax  1  oz.,  potassium  carbonate  1  oz.,  fused  into  a 
glass  and  ground  fine.  The  oxide  is  placed  in  a  smooth  Wedg- 
wood mortar  and  ground  separately  as  fine  as  it  is  possible  to  get  it. 
The  flux  is  then  added  in  small  quantities  and  the  levigation  continued^ 
after  which  the  feldspar  may  be  added  and  treated  similarly.  It  is  of 
the  highest  importance  that  the  mass  be  reduced  to  the  utmost  degree 
of  fineness,  and  an  expert  workman  will  spend  six  or  eight  hours  at 
least  in  levigating  the  quantity  given  in  the  formula.  While  the  mass 
is  being  ground  in  the  mortar  foreign  substances,  such  as  small  particles  of 
wood,  etc.,  must  be  carefully  excluded  ;  otherwise  during  the  vitrefying 
process  these  will  be  converted  into  carbon,  which  will  be  sure  to  reduce 
a  portion  of  the  gold  in  fine  metallic  globules  distributed  throughout 
the  mass. 

The  vitrefying  or  fritting  process  consists  in  packing  the  mass,  after  the 
most  thorough  levigation,  in  the  whitest  sand  crucible  that  can  be  obtained. 
(Dark-colored  crucibles  are  liable  to  injure  the  frit  by  contamination  with 
iron.)  This  must  be  provided  with  an  accurately  fitting  cover  made  of  the 
same  material,  or  a  suitable  top  may  be  formed  of  a  piece  of  slide  such  as 
is  used  in  burning  continuous-gum  work.  Before  placing  the  frit  in  the 
crucible  the  interior  surface  of  the  latter  should  receive  a  thin  coating 
of  very  fine  quartz,  made  into  a  paste  with  water,  to  prevent  the  frit 
from  adhering  to  it  during  fusion.  The  frit  in  the  dry  state  is  then 
packed  in,  and  the  cover  tightly  luted  to  its  place  with  kaolin.  The  cruci- 
ble is  then  to  be  buried  in  a  strong  anthracite-coal  fire,  and  to  remain  there 
until  the  contents  are  fused.  The  time  required  to  do  this  will  depend 
upon  the  size  of  the  crucible  and  the  intensity  of  the  heat.  Any  ordi- 
nary coal-stove  provided  with  a  good  draught  will  answer,  but  the  fuel 
must  be  packed  around  and  over  the  crucible,  and  the  heat  carried  to 
the  highest  attainable  point.  Usually  about  two  hours  will  be  required 
to  thoroughly  fuse  the  mass,  after  which  it  is  removed  from  the  fire  and 
permitted  to  cool. 

The  vitrefied  mass  is  removed  from  the  crucible  by  breaking  the  lat- 
ter. Every  particle  of  adhering  quartz  or  portions  of  the  crucible 
should  be  cleared  from  the  surface.  It  is  then  pulverized  to  a  fineness 
which  will  allow  it  to  pass  through  a  No.  10  bolting-cloth  sieve,  and  is 
ready  for  the  third  stage  in  the  preparation  of  gum -enamel,  which  con- 
sists of  diluting  the  frit  with  the  proper  amount  of  feldspar.  As  the 
strength  of  the  coloring  pigment  varies  according  to  the  degree  of  fine- 
ness attained  during  the  levigation,  it  is  usually  necessary  to  make 
several  tests  in  order  to  arrive  at  the  desired  shade.  This  is  accom- 
plished by  mixing  separately  several  different  lots  in  the  following 
proportions : 

Gum  frit 1  part;   I  Gum  frit 1  part;    j Gum  frit Ipart; 

Feldspar 2  parts.  |  Feldspar 3  parts.  1  Feldspar 4  parts. 

These  are  applied  to  marked  pieces  of  porcelain  body  and  fused  in 
the  usual  way,  the  result  determining  the  proportions  necessary  to  pro- 
duce the  desired  shade. 


FORMULAS  FOB  CONTTNUOUS-OUM  WORK.  223 

White  bottle-glass,  which  does  not  contain  lead  or  iron,  may  be  used 
as  "  flux  "  to  reduce  the  fusing-point  of  enamels,  but,  owing  to  the  un- 
certainty of  the  composition  of  glass,  most  of  the  manufacturers  of  por- 
celain teeth  make  a  fine  glass  for  this  purpose  after  the  formula  given 
on  p.  467,  the  ingredients  of  which  are  first  ground  separately,  then  thor- 
oughly mixed,  and  placed  in  a  white  crucible  provided  with  a  cover 
(which  must  be  tightly  luted)  and  thoroughly  fused.  If  perfectly  pure 
materials  are  used,  the  result  will  be  an  exceedingly  brilliant,  colorless, 
and  transparent  glass. 

Formulas  for  Continuous- gum  Work. 

Bodies  and  enamels  intended  for  use  in  the  "  continuous-gum  "  pro- 
cess must  necessarily  be  more  fusible  than  the  materials  of  which  teeth 
are  composed,  in  order  that  the  latter  may  not  be  aifected  by  the  three 
heatings  the  denture  must  be  exposed  to  before  it  is  completed.  It  will 
therefore  be  noticed  that  an  unusual  amount  of  flux  enters  into  their 
composition.  The  formulas  herein  given  are  those  of  well-known 
experts  in  continuous-gum  work,  and  for  further  information  in  the 
compounding  of  this  class  of  bodies  and  gum-enamels,  their  application 
and  management  during  vitrefaction,  the  reader  is  referred  to  the  chapter 
on  ■'  Continuous-gum  Work." 

Continuous-gum  Formulas  of  Dr.  Hunter. 


Flux:  Quartz 8    oz 

Calcined  borax 4 


Fuse  in  crucible  to  form  glass ;   when  cold 


Caustic  potash.    .'    .'    .'    .'    .'    1      «      |      reduce  to  powder. 

Granulated  Body :  Spar 2    oz.     'J    t-,  .  ...  ,  , 

Ouartz  1.^    "       i  ^^^^    ^°    crucible,   and   powder    to    pass 

Kaolin  '    '    '    '       i    a       j       through  No.  50  wire  sieve. 

Body :  Flux,  as  above 1    oz.     "|   Grind  the  first  two  articles  very  fine,  then 

Asbestos 2     "       j-      add  granulated   body,  which   is   mixed 

Granulated  body     .    .    .    .     IJ    "       j       with  the  fine  without  grinding. 

Gum  Enamel:  Flux,  as  above  .    .    1    oz.     ^   ,-,  .    ,  n  ^         ■  j.       •  ■^^ 

•  Fused  spar  1      "       I  ^'"'^'^^  "^^^^7  ""^  ^""  semi-fuse  m  crucible ;, 

English  rose-red    .'40    gr.     J       Powder  coarsely  for  use. 

Formulas  of  Dr.  D.  D.  Smith. 

Granulated  Body  :  Quartz  ....  20    gr.     "] 

Spar 24     "       !   Grind  fine  and  fuse  on  slide  in  furnace ;, 

Caustic  potash     1      "       j       powder  coarsely  for  use. 
Titanium  .    .  2  gr.-l  oz.  J 

i^te.-  Quartz,  very  fine 18    dwt.  ] 

Spar 10      "      I 

Glass  of  borax 2"-c,  ,  j-j  ^ 

Cryolite  ]       "      '    ^  use  same  as  above,  and  grind  very  fine. 

Caustic  potash 10    gr.      | 

Titanium IJ  gi'--l  oz.  J 

Gum  Enamel:  Gum  frit  of  (S.  S.  ] 

White)    .    .    .    .    U  dwt.    | 
Flux    without    ti-  \   -r^  j      •    j  i- 

tanium     .    .    .    .  16      "      f  Fuse  and  grind  tor  use. 

Granulated  body    .11      " 
Cryolite 7      "J 


224  MOULDING  AND  CARVING  PORCELAIN  TEETH. 

Dr.  Mqffifs  Formula  for  Continuous-gum  Body. 

Body :  Spar 12    oz.  ] 

Quartz 4J   "  | 

Bohemian  glass 60    gr.  |-  Grind  coarsely. 

French  china 35      "  | 

German  clay 2    dwt.  J 

^0  gum-enamel  formula  came  with  this.     Dr.  Smith's  formula  for  gum 
enamel  will  do  for  the  above,  minus  the  cryolite. 

Dr.  John  Allen's  First  Formulas,  now  Out  of  Use. 


Body:  Quartz 2    parts. 

Flint  glass 1    part. 

Borax 1       " 

Wedgwood IJ  parts. 

Asbestos 2    oz. 

Spar 2      " 

Kaolin 1      " 


Gum  Enamel :  Spar I5  oz. 

White  glass 1      " 

Oxide  of  gold  .    .    .    .  IJ  gr. 


(For  the  formula  of  Dr.  Ambler  Tees  see  Chapter  on  Continuous 
Gum  Work.) 

Shapes  and  Sizes  of  Teeth. 

Though  no  rules  can  be  formulated  by  which  the  dentist  can  be 
directed  with  precision  in  the  congruous  selection  and  arrangement  of 
the  artificial  substitutes,  yet  there  are  always  to  be  found  certain  tem- 
peramental characteristics  of  the  face  and  personnel  of  the  patient, 
together  with  age  and  sex,  which  will  be  of  much  value  in  this  branch 
of  prosthetic  dentistry. 

The  study  of  the  harmony  of  temperament  with  the  shape,  color,  and 
arrangement  of  human  teeth  should  claim  careful  attention  on  the  part 
of  the  manufacturer  of  artificial  teeth,  and  a  knowledge  of  the  teeth  of 
the  basal  temperaments  which  are  the  foundation  types  will  materially 
aid  him  in  the  production  of  life-like  forms  and  colors. 

It  is  true  that  amongst  patients  we  rarely  find  pure  types  of  the  dif- 
ferent basal  temperaments,  but  it  would  be  difficult,  if  not  impossible, 
to  recognize  the  numerous  modifications  of  the  temperamental  cha- 
racteristics of  teeth  had  we  not  to  a  certain  extent  studied  the  teeth  of 
these  types.  The  following  tables  give  the  relation  of  shape  and  color 
of  teeth  to  each  basal  temperament : 

Bilious  Temperament.  Sanguine  Temperament. 

Color  :  Color : 

Golden  yellow.  Soft  yellow. 

Shape :  Shape : 

Flat  face,  large  and  angular.  Round  face  and  bold.. 

Nervous  Temperament.  LymphatiG  Temperament. 

Color :           ■  Color : 

Transparent  blue  or  gray.  Opaque  white. 

Shape :  Shape : 

Graceful,  semi-round  face.  Spheroidal,  broad,  and  rather  short. 

There  are  numerous  modifications  or  combinations  of  the  basal  types, 
and  the  artistic  element  in  prosthetic  dentistry  consists  in  the  ability  to 


SHAPES  AND  SIZES  OF  TEETH.  225 

appropriately  select  such  samples  of  size,  shape,  and  color  as  will  be  in 
harmony  with  the  facial  peculiarities  of  the  patient. 

Individuals  of  the  bilious  temperament  usually  have  large  and  rather 
long  teeth,  nearly  as  broad  at  the  necks  as  at  the  cutting  edges,  which 
are  square  and  well  defined.  The  teeth  of  the  sanguine  temperament 
are  smaller  in  size,  distinctly  convex  on  their  faces,  and  tapering  at  their 
necks.  Teeth  belonging  to  the  nervous  types  are  usually  inclined  to  be 
long  and  slender,  with  convex  or  rounded  faces,  narrow  necks,  well- 
marked  longitudinal  indentations,  and  much  more  delicate  and  graceful 
in  form  and  outline  than  the  preceding  types.  Lastly,  types  of  teeth  of 
the  lymphatic  temperament  are  broad  and  short,  with  very  convex  faces, 
and  are  without  any  of  the  graceful  lines  of  those  of  the  nervous  type. 

Dr.  William  R.  Hall,  who  has  had  extensive  experience  in  the  manu- 
facture of  porcelain  teeth,  finding  that  the  descriptions  of  the  teeth  of 
the  four  basal  temperaments,  while  affording  a  general  idea  of  size  and 
shape,  were  not  definite  enough  to  be  of  much  use  practically,  collected 
a  large  number  of  natural  teeth  for  the  purpose  of  ascertaining  as  nearly 
as  possible  the  correct  outline,  exact  sizes,  and  other  characteristics  of 
the  natural  organs,  for  the  purpose  of  adopting  some  order  or  system 
that  would  serve  as  a  more  reliable  guide  in  the  production  of  life-like 
imitations  of  human  teeth  than  did  the  old  plan  of  one  unvarying  shape 
of  different  sizes,  which  was  the  rule  before  and  up  to  1865. 

Amongst  the  teeth  examined  by  Dr.  Hall  were  sixteen  sets  of  upper 
front  teeth,  such  as  were  previously  imported  from  Europe  for  pivoting  : 
many  of  them  had  probably  been  purchased  from  peasants  and  were 
well  matched  as  to  their  relative  sizes.  In  assorting  these  teeth  into 
groups  it  was  found  that  there  were  three  distinct  and  characteristic 
shapes,  representing  dissimilar  types.  They  were  therefore  divided  into 
three  classes,  which  have  been  found  to  embrace,  practically,  all  the 
desirable  forms  which  would  be  likely  to  be  demanded  in  prosthetic 
dentistry. 

In  the  study  of  this  classification  it  is  well  to  begin  Math  an  examination 
of  the  crowns  of  incisors,  bicuspids,  and  molars  of  both  upper  and  lower 
jaws — first,  because  these  are  indications  of  shape  and  temperament ; 
and  secondly,  with  the  view  to  acquiring  an  intimate  knowledge  of  their 
forms  and  arrangement,  so  that  in  carving  or  mould-making  they  may  be 
designed  in  such  manner  with  reference  to  occlusion  tliat  they  will,  when 
articulated  and  adjusted  to  the  mouth,  perform  the  function  of  mastica- 
tion with  some  degree  of  satisfaction  to  the  patient — a  result  at  present 
not  invariably  obtained.  This  is  a  part  of  the  process  of  making  arti- 
ficial teeth  to  which  but  little  attention  has  been  given.  Until  the  pub- 
lication of  Dr.  W.  G.  A.  Bonwill's  admirable  system  of  articulating  por- 
celain teeth  no  important  improvement  had  been  suggested,  and,  although 
Bonwill  described  his  method  more  than  a  quarter  of  a  century  ago,  it 
has  not  yet  received  the  recognition  either  by  the  dentist  or  manu- 
facturer to  which  it  is  entitled. 

The  teeth  of  the  first  class  are  those  with  round  or  convex  faces,  the 
greatest  convexity  being  from  the  proximate  surfaces,  with  the  lesser  con- 
vexity from  the  neck  to  cutting  edge.  Teeth  of  this  class  have  necks 
inclined  to  be  broad. 

In  the  second  class  were  found  teeth  with  semi-round  faces,  graceful 

15 


226  MOULDING  AND   CARVING  PORCELAIN  TEETH. 

in  outline,  narrower  necks,  and  much  less  rounding  on  their  labial  sur- 
faces than  the  preceding. 

The  third  class  consisted  of  flat-faced  teeth,  more  angular,  with 
square  forms,  and  no  appearance  of  grace  in  their  outlines. 

It  must  not  be  supposed  that  the  teeth  in  each  of  these  classes  were 
of  the  same  size  :  on  the  contrary,  they  varied  greatly  in  that  respect, 
both  in  width  and  length  of  crowns,  as  well  as  in  width  and  narrowness 
of  the  necks.  This  necessitated  a  further  subdivision  of  the  three 
classes  :  accordingly,  the  maximum  and  minimum  widths  and  lengths  of 
the  crowns  were  measured  and  noted  in  forty-eighths  of  an  inch,  this 
fractional  part  of  an  inch  being  chosen  on  account  of  its  convenience 
and  the  ease  with  which  it  may  be  discerned  by  the  eye.  Impressions  of 
the  convexities  of  the  faces  and  outlines  of  the  proximate  surfaces 
were  taken  in  plaster  for  the  purpose  of  making  w^orking  models  to  be 
carefully  kept  as  future  guides. 

The  maximum  size  of  the  superior  central  incisors  was  found  to  be 
20  forty-eighths  of  an  inch  in  width  at  their  cutting  edges ;  the  crowns 
from  cutting  edge  to  neck  measured  24  forty-eighths  of  an  inch  in 
length ;  while  the  widths  of  the  necks  varied  from  16  to  18  forty- 
eighths  of  an  inch. 

The  cutting  edges  of  the  smallest  central  incisors  measured  14  forty- 
eighths  of  an  inch  in  width  and  16  forty-eighths  in  length  of  crown; 
while  the  necks  measured  from  10  to  12  forty-eighths  in  width. 

In  studying  the  relative  sizes  it  was  found  that  the  superior  lateral 
incisors  were  uniformly  two  sizes  smaller  in  length  and  width  than  the 
centrals  of  the  same  set — a  size  being  1  forty-eighth  of  an  inch.  The 
superior  cuspids  were  of  the  same  length  as  the  centrals,  and  about 
one  size  narrower.  The  bicuspids  were  four  sizes  narrower  and  two 
sizes  shorter  than  the  centrals.  The  relative  size  of  the  molars  of  a  set  of 
anterior  teeth  given  above  would  probably  be  from  18  to  22  forty-eighths 
of  an  inch  in  width  and  from  14  to  18  in  length.  In  general  the  outer 
or  buccal  cusps  of  the  bicuspids  and  molars  are  longer  than  the  palatal. 

Lower  teeth,  according  to  the  result  of  Hall's  investigations,  vary 
somewhat  in  form,  but  the  varieties  of  shapes  are  not  as  numerous  as 
those  found  in  upper  sets.  He,  however,  made  two  distinct  classifica- 
tions— the  round  and  flat-faced  with  narrow  necks,  and  the  round  with 
broad  necks.  The  widths  of  the  lower  centrals  were  from  7  to  10 
forty-eighths  of  an  inch,  the  length  from  16  to  20  forty-eighths.  The 
lower  laterals  were  of  the  same  length  as  the  centrals,  but  in  width  they 
exceeded  them  by  two  sizes.  The  lower  cuspids  were  two  sizes  wider 
than  the  laterals  and  one  size  longer.  The  bicuspids  and  molars  will 
not  be  found  to  differ  greatly  in  length  and  width  from  the  upper  teeth 
of  the  same  set,  but  in  lower  dentures  the  inner  cusps  are  generally 
longer  than  the  outer  ones. 

The  following  is  a  table  ^  of  widths  derived  from  measurement  of 
natural  teeth  herein  described.  These  widths  apply  to  all  the  three 
classes,  and  are  believed  to  be  sufficient  in  range  to  meet  all  ordinary 
requirements.  The  No.  1  centrals,  laterals,  cuspids,  bicuspids,  and 
molars  form  one  set ;  No.  2,  a  narrower  set :  No.  3,  still  narrower ;  and 
so  on  to  No.  5  : 

'  American  System  of  Dentistry. 


SHAPES  AND  SIZES  OF  TEETH.  227 

Widths  for  all  Classes  of  Teeth. 
Centrals No.  ],  if ;  No.  2,  Hi  No.  3,  if;  No.  4,  ||;  No.  5,  if. 

T,sifpral«  "  i£  ■  "  1^-  "  lA.         "  13.        «  12 

r:nninp<5  "  1'-.  "  ifi  .  "  15.         ((         14.        «         13 

Bicuspids     '•  it;  "  if;  "  if. 

Molars "  |f;  '•  ||;  "  if. 

Below  is  a  list  of  thirty  additional  sets  needed  to  complete  the  scheme 
described  in  the  foregoing  classifications.  This  number  of  sets  are  thus 
augmented  to  ninety,  making  an  assortment  of  plain  teeth  large  enough 
for  all  practical  purposes  : 

First  Class  :  Bound  Face,  with  Broad  Necks. 

Five  sets,  widths  as  numbered,  1,  2,  3,  4,  5,  and  f|  long. 


¥8 

16  << 


Narrov)  Necks. 


Five  sets,  widths  as  numbered,  1,  2,  3,  4,  5,  and  |f  long. 

((  (1  i(  it  2  0       a 

II  CI  II  il  16.         li 

These  thirty  sets  constitute  all  of  the  first  class. 

Second  Class  :  Semi-round  Face,  with  Broad  Necks. 

Five  sets,  widths  as  numbered,  1,  2,  3,  4,  5,  and  f|  long. 

"  H  U  il  20         <( 

((  i(  a  (c  16       « 

¥8 

Narrow  Necks. 

Five  sets,  widths  as  numbered,  1,  2,  3,  4,  5,  and  ff  long. 

"  *'  "  (1  20       a 

"  "  il  u  fe       it 

¥8' 

Thirty  more  sets,  constituting  all  of  the  second  class. 

Third  Class  :  Flat  Face,  Broad  Necks. 

Five  sets,  widths  as  numbered,  1,  2,  3,  4,  5,  and  f|  long. 

"  "  "  a  20       « 

"  «<  "  «  Il       « 

¥8 

Narrow  Necks. 

Five  sets,  widths  as  numbered,  1,  2,  3,  4,  5,  and  ff  long. 

"  "  >'      ■  il  20         " 

"  "  "  il  16  li 

¥'8 

While  the  study  of  the  foregoing  classification  of  shapes  and  sizes 
would  be  a  great  help  to  manufacturers  of  artificial  teeth,  it  must  not 
be  supposed  that  even  the  most  intimate  knowledge  of  it  or  of  any 
other  system  will  reduce  the  selection  and  assembling  of  the  porcelain 
substitutes  and  their  adjustment  to  the  mouths  of  patients  to  an  ordinary 
mechanical  operation.  From  this  system  of  Dr.  Hall  there  are  doubt- 
less almost  unlimited  deviations,  and  it  was  clearly  his  aim  in  making 
the  classification  and  measurements  to  place  within  the  reach  of  manu- 
facturers a  practical  plan  which  might  take  the  place  of  the  haphazard 
methods  heretofore  pursued  in  that  "branch  of  industry.  Beyond  a  cer- 
tain point  the  interests  of  the  manufacturers  and  the  wants  of  the  den- 
tist are  neither  identical  nor  reciprocal.  The  latter  often  needs  teeth 
imitating  irregularities  of  position,  color,  etc.  designed  for  special  cases, 
the  production  of  which  the  manufacturer  is  not  prepared  to  attempt,  as 


228  MOULDING  AND  CARVING  PORCELAIN  TEETH. 

it  would  compel  him  to  depart  from  the  routine  work  of  his  factory — a 
course  which  he  would  find  unremunerative  ;  hence  the  dentist  must 
depend  much  upon  his  own  artistic  taste  and  skill  in  making  such 
changes  in  the  shapes  and  positions  of  the  teeth  obtained  from  the 
manufacturers  as  the  case  in  hand  demands.  This  can  be  better  done 
with  single  plain  teeth  than  with  either  sectional-block  or  single  gum 
teeth.  It  is  to  be  regretted  that  more  attention  has  not  been  given  to 
imitating  in  sectional-block  teeth  the  changes  characteristic  of  age,  such 
as  the  recession  of  the  gums,  which  begins  in  many  cases  in  early 
middle  life  and  progresses  until  a  large  part  of  the  dentine  above  the 
crown  is  uncovered ;  the  loss  of  that  uniformity  of  color  which  con- 
tributes so  much  to  the  beauty  of  the  teeth  in  youth  ;  and  the  changes 
which  take  place  at  the  cutting  edges  of  teeth  as  years  advance.  The 
absence  of  these  details  is  largely  the  cause  of  the  gradual  discon- 
tinuance of  the  use  of  sectional  blocks.  Really  artistic  teeth  in  blocks 
or  sections  should  cost  no  more  to  produce,  after  the  designs  and  moulds 
are  made,  than  do  the  inartistic  and  conventional  sets  which  we  find  in 
such  abundance  at  the  manufacturer's. 

Unusual  shapes  of  teeth  are  sometimes  demanded  for  special  cases, 
when  the  prosthetic  dentist  must  depend  upon  his  own  resources  for 
their  production.  We  occasionally  need  exaggerated  examples  of  teeth 
of  the  third  class  referred  to  on  p.  227,  described  as  flat-faced,  wherein 
the  flatness  goes  so  far  as  to  nearly  constitute  a  concavity  of  the  face  of 
the  tooth.  When  this  is  the  case  it  will  be  found  impossible  to  secure 
such  teeth  from  the  dental  depots,  and  the  dentist  must  depend  upon  the 
corundum  wheel,  with  which  he  may  make  such  changes  as  are  required. 
This  may  be  done  by  using  a  wheel  of  the  finest  grit,  after  which  the 
ground  surface  of  the  porcelain  may  be  polished  with  a  small  wheel 
made  of  Arkansas  stone,  followed  by  a  small  wooden  wheel  armed  with 
oxide  of  tin  mixed  with  water.  This  may  be  done  with  the  teeth  of  any 
of  the  manufacturers,  but  it  is  especially  successful  when  teeth  of  Eng- 
lish make  are  used,  they  being  formed  of  porcelain  of  such  closeness  of 
texture  that  they  may  be  ground  and  polished  without  any  material 
change  in  the  surface. 

On  the  other  hand,  it  is  sometimes  necessary  to  make  additions  to 
teeth  in  order  to  bring  their  forms  to  correspond  with  unusual  shapes  of 
remaining  natural  organs.  An  instance  of  this  occurred  recently  in  the 
author's  practice,  in  which  he  found  it  impossible  to  match  the  shapes 
of  some  very  peculiar  lower  incisors.  These  teeth  had  from  early  child- 
hood projected  so  far  beyond  the  upper  incisors  as  to  be  practically  use- 
less in  the  incision  of  food  ;  as  a  consequence,  the  corrugations  which  are 
seen  in  the  incisor  teeth  of  children  were  still  present,  although  the 
patient  was  nearly  fifty  years  of  age.  The  natural  teeth  had  become  so 
loosened  that  their  loss  was  a  question  of  a  short  time  ;  they  were  broad 
at  the  cutting  edges  and  unusually  round  on  their  faces.  This  promi- 
nence made  them  a  noticeable  feature  of  the  patient's  face,  and  after  the 
first  attempt  to  substitute  porcelain  teeth  it  was  seen  that  any  departure 
from  the  form  and  size  of  the  natural  organs  greatly  changed  the  ex- 
pression of  the  mouth.  The  difficulty  was  finally  overcome  by  selecting 
the  exact  color  from  the  enamels  furnished  with  the  "  Downey  furnace," 
described  on  p.  260.     The  faces  of  the  teeth  were  built  upon  with  this 


SHAPES  AND  SIZES  OF  TEETH.  229 

material,  which  fuses  at  a  much  lower  degree  of  heat  than  do  the  bodies 
and  enamels  of  ordinary  porcelain  teeth.  They  were  then  burned 
separately  in  the  Downey  furnace  of  the  pattern  recommended  for  crown- 
work,  the  corrugations  having  previously  been  cut  in  them  with  a 
corundum  wheel.  The  result  was  so  successful  that  it  established  the 
value  of  the  Downey  furnace  as  a  most  useful  accessory  of  the  author's 
laboratory. 

The  relative  positions  of  teeth  in  the  present  state  of  tooth  manu- 
facture belongs  almost  exclusively  to  the  dentist  himself.  In  the  as- 
sembling of  fourteen  teeth  in  the  construction  of  an  upper  artificial 
denture  he  should  bear  in  mind  that  teeth  are  lost  through  two  principal 
causes — namely,  the  ravages  of  decay  and  premature  loosening  (pyorrhoea 
alveolaris).  In  the  first  case,  decay  usually  begins  early  in  life,  and 
generally  before  the  teeth  are  finally  lost  some  have  become  devitalized — 
a  condition  necessarily  accompanied  by  change  in  color.  This  is  an 
important  feature  in  the  general  eifect  of  an  artistically  arranged  den- 
ture, and  the  almost  total  neglect  on  the  part  of  both  manufacturer  and 
dentist  to  imitate  it  is  one  of  the  prominent  causes  for  the  glaring  un- 
naturalness  of  their  products. 

Teeth  of  the  frailest  class,  which  have  been  constantly  filled  and 
refilled  up  to  middle  age,  will  generally  be  found  to  have  lost  much  of 
the  appearance  of  regularity  which  they  may  have  had  in  early  youth. 
These  defects  should  to  a  certain  extent  be  imitated.  To  be  natural  in 
appearance  teeth  must  be  inconspicuous,  in  the  sense  that  they  must  not 
attract  unusual  notice.  What  then  could  be  more  startling  to  the  friends 
and  relatives  of  a  patient,  whose  teeth  had  always  required  constant 
attention  on  the  part  of  the  dentist,  than  for  him  to  suddenly  appear  with 
a  denture  of  pearly  whiteness,  painfully  regular,  and  in  all  respects  better 
suited  to  the  age  of  sixteen  or  eighteen  than  to  late  middle  life  ? 

Fig.  263. 


In  the  arrangement  of  teeth  serious  errors  are  constantly  made  by  the 
dentist.  The  work  is  usually  considered  well  done  if  a  perfectly  sym- 
metrical arch  has  been  obtained,  whereas  in  life  we  rarely  find  a  fault- 
lessly regular  arch. 

Referring  again  to  the  classifications  of  shapes  and  sizes  which  have 
been  considered,  we  not  unfrequently  find  in  the  third  class  the  flat-faced, 
angular  teeth  of  that  type  standing  perpendicularly  or  nearly  so,  and 
at  their  distal  approximate  sides  either  quite  straight  (Fig.  263)  or  turned 
slightly  outward  (Fig.  264).  In  the  first  class  of  round-faced  teeth  with 
broad  necks  the  positions  of  the  centrals  are  nearly  perpendicular,  with 
perhaps  a  slight  inclination  toward  the  centre  line. 


230  MOULDING  AND   CARVING  PORCELAIN  TEETH. 

In  the  second  class  the  teeth  will  be  found  to  stand  with  a  slight  in- 
clination toward  the  centre  line,  from  which  the  incisors  are  the  starting- 
point  of  a  symmetrical  curve  (Fig.  265). 

Fig.  264. 


In  the  arrangement  of  teeth  with  reference  to  the  inclination  of  the 
front  teeth  backward  or  forward,  corresponding  to  the  conformation  of 
the  face,  three  somewhat  hypothetical  divisions  of  physiognomies  are 
made.  The  first  class  is  a  type  of  the  Anglo-Saxons  or  their  Anglo- 
American  descendants  :  these  are  described  as  having  oval  cranial  con- 
tour, with  forehead  slightly  sloping,  maxillary  bones  equal  in  length,  the 
position  of  the  teeth  perpendicular  or  nearly  so,  to  which  is  due  the  firm 
expression  of  the  mouth  supposed  to  be  observed  in  the  facial  expression 
of  the  unmixed  native  population  of  the  United  States. 

The  second  class  is  not  confined  to  any  particular  nationality,  and  is 
distinguished  by  poor  development  of  the  lower  jaw,  resulting  in  a  re- 
treating chin.     The  faces  of  individuals  of  this  type  have  a  weak  ex- 
pression,   and    may    be    found 
Fig.  265.  amongst    any    nation    or    class 

of    people.       Its    direct    effect 
upon  the  teeth  is  to  cause  the 
upper  incisors  to  incline  back- 
ward to  meet  the  lower  teeth. 
Upper  teeth  carved  or  arranged 
to  suit  articulations  of  this  class 
should  incline  somewhat  back  of  the  perpendicular,  while  the  lower  teeth 
should  incline  forward,  so  that  they  may  pass  just  inside  of  the  superior 
incisors  and  cuspids. 

The  third  type,  which  is  found  chiefly  amongst  a  certain  class  of 
Celtic  origin,  is  marked  by  upper  and  lower  jaws  of  great  prominence, 
causing  the  teeth  to  protrude  at  a  sharp  angle  at  the  cutting  edges.  In 
this  facial  type  both  jaws  incline  forward  at  an  angle  of  from  70°  to 
80°  ;   the  upper  lip  is  long  and  without  graceful  curves. 

The  facial  types  above  considered  refer  to  individuals  with  full  den- 
tures, and  will  serve  in  a  general  way  to  illustrate  the  inclinations  which 
may  be  found  necessary  to  the  maintenance  of  the  natural  expression  of 
the  patient's  face. 

There  is  another  point  of  importance  in  the  manufacture  and  arrange- 
ment of  artificial  teeth  which  deserves  notice  before  the  details  of  their 
production  are  considered.  This  is  the  fact  that  in  nearly  all  normal 
natural  dentures  the  teeth  are  in  contact  and  each  tooth  supports  its 
neighbor.     Teeth  that  stand  alone  and  are  without  lateral  support  are 


CARVING  BLOCK  TEETH.  231 

liable  to  become  loosened  by  the  strain  of  mastication.  It  is  evident 
that  this  provision  of  nature  is  for  the  purpose  of  preventing  too  much 
force  from  being  thrown  upon  the  socket  of  any  one  tooth,  yet  all  the 
sectional-block  teeth  that  are  made  have  permanent  separations  between 
them.  Natural  teeth  with  separations,  when  such  a  condition  in  the 
positions  of  teeth  does  occasionally  occur,  impart  a  peculiar  expression 
to  the  mouth  and  face,  and  porcelain  teeth  so  arranged  are  at  once  recog- 
nized as  artificial.  Spaces  should  never  be  made  between  artificial  teeth 
unless  it  be  done  to  imitate  a  similar  peculiarity  previously  existing  in 
the  natural  denture. 

Carving  Block  Teeth. 

The  early  workers  in  this  art  seem  to  have  striven  for  entirely  dif- 
ferent results.  The  object  of  one  worker  was  to  compound  bodies  and 
enamels  which  would  maintain  their  form  during  the  vitrefying  process, 
regardless  of  color,  translucency,  and  texture ;  that  of  another,  the  secur- 
ing of  all  these  qualities  at  the  expense  of  stability  during  burning.     Fig. 

266  shows  a  set  of  teeth  carved  by  Joseph  E.  Mcllhenny  about  1835  ;  Fig. 

267  represents  a  block  carved  by  Prof.  Wildman  some  years  later.  The 
first  has  maintained  the  form  and  position  of  the  teeth  while  fusing,  but 
the  amount  of  clay  used  to  secure  these  qualities  has  imparted  to  the 
teeth  the  opaque  and  cloudy  appearance  sometimes  seen   in  devitalized 

Fig.  266. 


Showing  faces  of  front  teeth,  carved  by  J.  E.  Mcllhenny. 

teeth.     In  the  block  carved  by  Prof.  Wildman  the  teeth  have  graceful 
lines,  and  in  color,  translucency,  and  life-like  texture  have  not  been  ex- 
celled up  to  this  time  ;  but  the  great  spaces 
between  the  teeth  due  to  shrinkage  of  tlie 
body  gives  them  a  most  unnatural  appear- 
ance. 

The  carved  teeth   of  fifty   years  ago 
were  generally  arranged  with  holes  through     ^,  ^^   „   ^„r... 

,         '='  „  .  *'     .  T-»    j^i         i?    j_i  •         Block  carved  by  Prof.  Wildman,  bhow- 

them    lOr    riveting.       l^otn    OI     the     SpeCl-  ing  spaces  caused  by  shrinkage  of 

mens  of  the  work  of  Wildman  and  Mc-       '^"'^^' 

Ilhenny  were  so  constructed,  as  shown  in  Fig.  268.  This  was  done 
to  avoid  the  danger  of  fracture  during  "  heating  up "  preparatory  to 
soldering.  As  improvements  were  made  in  the  composition  of  bodies 
and  enamels  the  quality  necessary  to  enable  them  to  withstand  high 
temperatures  was  secured  without  loss  of  life-like  color  and  texture. 

Carving  block  teeth  is  a  delicate  art,  requiring  skill,  experience,  and 
artistic  taste.  The  simplest  natural  objects  need  skill  and  training  in 
their  imitation.     The  beginner  need  not  expect  to  faithfully  reproduce 


232 


MOULDING  AND   CARVING   PORCELAIN  TEETH. 


Showing    arrangement    for  uniting    blocks    to 
plates :  teeth  made  by  Mcllhennj'. 


the  forms  of  natural  teeth  in  porcelain  without  first  having  studied  the 
shapes  of  many  different  types  of  those  organs,  when,  if  he  possesses 
artistic  ability,   more   or  less   success  may  attend  his  efforts. 

Hand-carved  blocks  have  not 
Fig.  268.  reached  a  very  high  standard  as 

reproductions  of  the  natural  or- 
gans, and  are  inferior  from  an 
artistic  standpoint  to  the  sectional- 
block  teeth  of  the  best  manu- 
facturers of  the  present  time.  The 
works  of  the  few  carvers  who  have 
given  their  attention  to  this  branch 
of  tooth-making  are  exceedingly 
conventional,  and  vary  only  in 
size :  hence  carved  block  teeth 
have  become  nearly  obsolete.  In 
carved  work  the  liability  to  warp- 
age  and  "  sprawling  "  of  the  teeth 
is  greater  than  in  moulded  work, 
and  chance  has  much  to  do  with 
the  final  result. 
Where  teeth  are  to  be  carved  for  special  cases  it  is  necessary  to 
first  finish  the  plate,  and  then  obtain  the  wax  articulation,  care  being 
taken  to  get  the  exact  height  and  fulness  required  by  the  case.  The 
correct  centre  line  is  then  to  be  marked.  The  plate,  with  the  trimmed 
wax,  is  placed  on  the  plaster  model :  in  the  sides  of  the  model  concave 
retaining-points  are  cut  to  assist  in  retaining  the  outside  walls  of  plaster, 
the  formation  of  which  is  the  next  step  in  the  operation.  The  model  is 
then  varnished,  allowed  to  dry  thoroughly,  and  then  oiled.     The  })laster 

is  mixed  rather  thick  and  built  upon 
the  model  with  a  steel  spatula  until 
it  entirely  covers  model  and  wax  ar- 
ticulation to  the  thickness  of  half  an 
inch  :  it  should  extend  above  the 
edge  of  the  wax  to  a  little  more 
than  one-eighth  of  the  proposed 
length  of  the  block,  to  allow  for 
shrinknge  in  burning. 

The  walls  are  usually  made  in 
three  sections,  the  two  side  walls 
being  made  first,  and  the  front  wall 
next,  each  wall  being  made  somewhat 
longer  than  the  required  length  of 
the  block,  to  compensate  for  shrink- 
age. A  vent-groove  must  be  cut  at 
and  below  the  edge  of  the  gum  to 
receive  the  excess  of  body  (Fig. 
270).  The  surface  of  the  walls 
against  which  the  plastic  body  is  to 
be  moulded  must  be  lined  with  tin-foil,  made  to  adhere  to  the  plaster 
by  means  of  shellac  varnish.     The  inside  wall   is  made   by  building  a 


'^^UIL.-^ 


CARVING  BLOCK  TEETH. 


233 


mass  of  plaster  upon  the  plate  and  against  the  inside  of  the  articulating 
wax.  This  should  also  be  lined  with  tin-foil.  Fig.  269  shows  the  cast  with 
the  articulating  wax,  the  inside  wall  (A),  and  outside  walls  (D  E  F)  in 
position. 

Fig.  270  shows  all  the  pieces  separately — the  inside  wall  by  A ; 
the  articulating  wax  by  B  ;  the  model  by  C ;  the  inside  walls  hy  D  E  F ; 
the  vent-grooves  by  the  dark  line  in  the  three  latter. 

Fig.  270. 


Mixing-  and  Moulding-  the  Body. — The  dry  body  is  mixed  with 
perfectly  clear  water,  to  which  has  been  added  gum  tragacanth,  8  grains 
to  the  pound  of  body.  Freslily  mixed  body  is  too  friable  for  either 
moulding  or  handling.  It,  however,  acquires  plasticity  and  toughness 
by  age,  and  is  greatly  improved  by  being  kept  wet  for  several  weeks 
before  using. 

The  composition  is  mixed  in  a  suitable  porcelain  or  glass  vessel  to  the 
consistency  of  cream,  and  poured  into  a  porcelain  bowl  and  allowed  to 


234 


MOULDING   AND   CARVING  PORCELAIN  TEETH. 


settle.  When  the  water  on  top  is  quite  clear  it  is  drained  off  by  tipping 
the  bowl,  care  being  taken  to  prevent  any  of  the  composition  from  flow- 
ing out  with  it.  To  prevent  any  of  the  coarser  parts  of  the  body  from 
settling  to  the  bottom,  it  must  be  mixed  again  very  thoroughly  by  means 
of  an  ivory  or  bone  spatula :  this  must  be  done  with  the  utmost  care,  to 
prevent  air-bubbles  from  being  confined  in  the  body,  as  such  an  accident 

Fig.  271. 


B  c 

Carving  instruments. 


might  be  the  cause  of  complete  failure  of  one  of  the  blocks ;  for  if  the 
smallest  portion  of  air  becomes  enclosed  in  the  block  and  escapes  detec- 
tion, it  may  expand  enormously  during  the  burning  process  and  distort 


CARVING  BLOCK  TEETH. 


235 


the  block  beyond  remedy.  The  jarring  cau.sed  by  gently  pounding  the 
bowl  on  the  table  will  often  induce  disengagement  of  air-bubbles  and 
force  them  to  the  top.  The  body  is  next  to  be  freed  of  its  surplus 
moisture  by  gentle  heat,  which  also  further  assists  in  the  expulsion 
of  air.  When  it  acquires  the  consistency  of  fresh  putty  pieces  can 
be  cut  off  as  required  for  moulding.  The  remainder  must  be  kept  tightly 
covered,  and  sufficient  water  occasionally  added  to  keep  the  mass  plastic. 
The  inside  wall,  A,  is  now  placed  in  position,  and,  together  with  the 
outside  wall,  E,  and  that  portion  of  the  plate  to  be  covered  by  the  block, 
given  a  thin  coat  of  olive  oil.  A  piece  of  body  somewhat  larger  than  is 
required  in  the  formation  of  the  block  is  cut  from  the  mass  and  worked 
with  the  fingers  to  a  convenient  shape  on  a  slab  of  plate  glass  or  porce- 
lain tile  :  by  a  sliding  motion  it  is  then  lifted  from  the  slab  and  placed 
on  the  model,  and  with  the  fingers  worked  against  the  inside  wall  in  the 
space  upon  the  ridge  previously  occupied  by  the  articulating  wax,  B. 
The  outside  wall  is  now  quickly  applied  with  sufficient  firmness  to  bring 
it  quite  close  to  the  model ;  the  vent-groove  shown  by  the  dark  line  on 
the  walls  in  Fig.  270  will  prevent  any  resistance  being  met  with  in  the 
surplus  body,  which  otherwise  might  be  forced  between  the  wall  and 
model. 

The  walls  are  held  in  position  until  the  body  is  dry  enough  for  their 
safe  removal.  The  drying  is  done  by  applying  heat  to  the  outside  of  the 
walls  with  the  flame  of  a  spirit-lamp  : 

the  walls  are  then  removed,  and    the  Fig.  272. 

moulded  block  lifted  with  great  care 
from  the  model  and  placed  under  a 
bell-glass  until  needed. 

Tools  Used  in  Carving  Blocks. 
— These  are  few  in  number  and 
simple  in  character.  Figs.  271  and 
272  represent  the  carving  tools  :  D, 
a  small  penknife  blade  set  in  a  han- 
dle of  cedar  or  poplar  wood  on 
account  of  its  lightness,  is  the  carving 
knife  and  performs  the  greater  part  of 
the  work ;  A,  string  bow  formed  by 
stretching  a  piece  of  fine  cotton  thread 
across  the  bend  of  a  piece  of  whale- 
bone about  7  inches  in  length ;  B,  pro- 
portional dividers,  shown  half  size  in 
the  illustration ;  C,  enamel  tool ;  E, 
bone  spatula ;  F,  spoon  scraper ;  G, 
drill,  made  by  flattening  and  tempering 
a  piece  of  steel  wire ;  H,  excavators 
for  cavities ;  I,  pin-tweezers.  The 
cuts  give  actual  sizes  of  all  the  instru- 
ments except  the  dividers. 

All  bodies  contract  in  burning,  the 
amount   of    contraction    depending   to 
some  extent  upon  their  composition  and  the  amount  of  compression  they 
receive  before  burning  :    thus,  carved  blocks  will  contract  about  one- 


F 


Carving  instruments. 


236  MOULDING   AND   CARVING  PORCELAIN  TEETH. 

sixth  of  their  entire  bulk,  and  moulded  blocks  somewhat  less.  Hall 
gives  one-eighth  as  the  allowance  generally  made  for  shrinkage  and 
loss  in  grinding  to  fit  the  plate  after  burning,  but  he  refers  to  the 
body  alone,  and  does  not  include  in  the  "  one-eighth  "  given  the  addi- 
tional shrinkage  of  the  point  enamel  added  after  the  shrinkage  allow- 
ance is  made  in  the  carving  previous  to  biscuiting.  If  the  shrinkage 
were  to  be  measured  by  instruments  of  precision,  it  would  probably  be 
found  to  be  about  one-sixth. 

The  allowance  for  shrinkage  is  arranged  with  the  proportional  divi- 
ders set  to  one-eighth  increase,  the  short  points  being  used  to  measure 
the  articulating  wax  from  gum  edge  to  articulating  edge.  The  respective 
distances  are  marked  on  the  cast  as  shown  on  G,  Fig.  270. 

The  block  is  carefully  placed  on  the  plate  and  suppprted  by  the 
inside  wall ;  the  proper  height  with  shrinkage  allowance  is  then  scribed 
on  it  with  the  adjusted  dividers,  one  point  resting  in  the  horizontal  line, 
while  the  other  touches  the  block.  By  drawing  it  gently  along  the  top 
of  the  block  a  distinct  mark  is  made,  indicating  the  point  to  which  it  is 
to  be  cut  down.  This  cutting  down  is  done  by  removing  the  block  and 
lightly  grasping  it  between  the  thumb  and  index  finger  of  the  left  hand, 
with  the  middle  finger  curved  under  it  in  a  manner  to  form  a  cushion  or 
support  for  it.  The  knife  is  then  brought  into  use,  and  all  material 
above  the  line  made  by  the  dividers  cut  away.  So  fragile  is  the  un- 
burned  body  that  the  slightest  excess  of  pressure  may  crush  the  block  : 
a  gentle  yet  firm  handling  of  the  unburned  material  will,  however,  come 
to  many  workmen  with  practice,  but  there  are  undoubtedly  some  who 
never  can  acquire  the  ability  to  go  through  the  different  stages  of 
carving  an  entire  upper  and  lower  denture  without  an  accident,  for  the 
blocks  must  be  taken  up  and  put  down  many  times  before  they  are 
ready  for  the  final  burning. 

Fig.  273. 


Method  of  holding  block  when  carving  the  labial  side. 

The  widths  of  teeth  are  next  to  be  marked  off  on  the  block.  This  is 
done  by  first  marking  the  centre  line,  and  then  indicating  on  each  side 
of  it,  by  a  shallow  incision  in  the  body,  the  desired  size  of  the  centrals : 


CARVING  BLOCK  TEETH..  237 

if  the  latter  be  medium  in  width,  the  laterals  should  be  two  sizes  nar- 
rower, cuspids  one  size  narrower,  than  the  centrals.  In  arranging 
for  shrinkage  a  good  plan  is  to  select  either  a  natural  or  porcelain  tooth 
of  the  desired  size,  which,  for  the  sake  of  example,  may  be  assumed  as 
16  forty-eighths  of  an  inch  wide.  The  width  in  carving  must  be  in- 
creased 'to  allow  for  shrinkage,  so  that  after  burning  the  carved  teeth 
will  be  exactly  the  size  of  the  sample.  To  accomplish  this  the  sample 
tooth  is  measured  by  the  small  points  of  the  dividers ;  the  large  points 
will  indicate  the  increase. 

In  the  first  carving  no  attempt  is  made  to  obtain  precision  of  form  or 
full  relief,  as  shown  in  Fig.  273.  The  teeth  are  but  superficially  laid 
out,  and  purposely  left  flatter  than  would  be  desirable  when  finished. 
The  first  step  is  to  cut  an  inverted  A-shaped  space  at  the  centre  line  to 
represent  the  space  between  the  central  teeth  :  this  is  repeated  between 
centrals  and  laterals  and  laterals  and  cuspids.  The  edges  are  slightly 
rounded,  and  by  a  circular  cut  of  the  knife-point  the  necks  of  the  teeth 
are  formed,  while  at  the  same  time  the  correct  lengths  are  given  them. 

During  this  preliminary  work  the  block  is  held  gum  upward  :  it  is 
now  to  be  reversed  and  the  points  of  the  gum  between  the  teeth  are 
carved  down,  and  both  ends  of  the  blocks  cut  square  for  jointing  to  the 
side  blocks.  The  inside  is  then  trimmed  to  the  proper  thickness,  and 
the  sulci  or  depressions  peculiar  to  the  palatal  surfaces  of  incisors  and 
canines  are  formed  with  the  instrument  F,  shown  in  Fig.  272.  Separa- 
tions are  made  with  the  bow-saw  A  (Fig.  271).  The  block  is  then  ready 
for  the  platinum  pins.  If  the  blocks  are  to  be  soldered,  a  level  surface 
is  left  from  the  point  at  which  the  palatal  surfaces  of  the  teeth  end  to 
the  portion  intended  to  rest  upon  the  plate.  Into  this  level  surface  holes 
are  drilled  for  the  reception  of  the  pins.  These  holes  are  made  by  rotat- 
ing a  small  drill,  as  shown  in  G  (Fig.  272),  between  the  thumb  and  index 
finger.  The  drill,  made  of  a  piece  of  No.  20  steel  wire  with  the  end 
flattened  to  the  width  of  No.  13  of  the  standard  gauge,  will  form  a  hole 
large  enough  for  the  reception  of  the  head  of  the  pin.  Two-thirds  of 
the  pin  should  be  imbedded  in  the  block.  The  pins  are  put  in  position 
by  means  of  the  tweezers  shown  in  Fig.  272,  and  a  thin  mixture  of  body 
and  water  floated  around  them  by  means  of  a  small  camel's-hair  pencil, 
care  being  taken  that  the  mixture  is  carried  quite  down  to  the  heads  of 
the  pins  without  enclosure  of  air. 

If  the  blocks  are  designed  for  mounting  on  rubber  base,  a  recess  must 
be  made  for  the  pins,  as  shown  in  Fig.  275.  If  the  blocks  are  very 
fragile,  the  holes  may  be  drilled  and  the  pins  put  in  after  they  are 
biscuit-burned. 

Biscuiting. — Biscuit-burning  is  the  partial  vitrefying  of  the  blocks 
by  which  they  are  hardened  sufficiently  to  admit  of  handling  without 
danger  of  breaking,  and,  what  is  even  of  greater  importance,  their  form 
is  to  a  certain  extent  permanently  fixed,  so  that  they  will  not  become 
plastic  or  semifluid  when  the  wet  enamels  are  laid  on  them.  The  blocks 
are  placed  on  a  fire-clay  slab  called  a  "  slide,"  and  thoroughly  dried  by 
gentle  heat  before  they  are  put  in  the  muffle  and  exposed  to  a  bright-red 
heat.  The  burning  must  be  carried  beyond  the  point  where  the  body  can 
no  longer  be  softened  by  water,  and  yet  not  be  too  hard  to  cut.  It 
should  remain  porous  enough  to  absorb  the  water  from  the  enamels  as 


238  MOULDING  AND   CARVING  PORCELAIN  TEETH. 

they  are  laid  on,  otherwise  enamelling  will  be  found  impossible  or 
nearly  so.  The  slightest  glazing  of  the  surface  must  be  avoided. 
About  the  hardness  of  a  piece  of  cuttle-fish  bone  is  the  proper  condi- 
tion. The  biscuited  blocks  may  be  cooled  in  the  air  without  danger 
of  cracking. 

Enamelling-. — Enamels  should  be  kept  in  small  glass  jars  provided 
with  tight  stoppers  to  exclude  the  dust.  Each  enamel  must  be  carefully 
kept  from  accidental  admixture  with  others,  and  the  jars  should  be 
labelled  with  the  number,  color,  and  other  explanatory  remarks  written 
plainly  thereon.  A  small  piece  of  body,  with  some  of  the  enamel  fused 
on  it,  may  be  tied  to  the  jar ;  this  affords  absolute  accuracy  in  the  deter- 
mination of  the  color,  when  burned,  of  the  contents  of  each  jar. 

More  failures  occur  in  enamelling  than  in  any  other  part  of  block- 
carving.  Great  care  is  constantly  required  to  see  that  the  enamel  is 
laid  on  of  the  proper  thickness,  that  it  is  uniform  in  quantity,  that  it 
does  not  unite  with  the  body,  and  that  point  and  base  enamels  are  so 
applied  that  a  perfect  blending  of  the  two  colors  may  result.  The  coat 
of  enamel  on  the  teeth  and  gums  should  be  at  least  ^4^^  ^^  ^^  mah 
thick ;  the  development  of  the  translucency  of  the  spar  and  brilliancy 
of  the  colors  demands  at  least  that  quantity.  The  body,  having  clay  in 
its  composition,  is  opaque,  and  would  show  through  a  thinner  layer  of 
enamel  and  impart  to  the  teeth  a  flat  and  lifeless  appearance. 

In  mixing  enamels  15  grains  of  gum  arable  to  each  ounce  of  enamel 
is  used,  to  prevent  the  coloring  materials  from  settling  when  mixed  with 
water,  to  make  the  enamel  work  smoothly,  and  to  enable  it  to  be  handled 
when  dry  without  rubbing  off. 

In  addition  to  the  point  and  base  (neck)  enamels  alluded  to  in  the 
description  of  the  manufacture  of  these  materials,  there  is  a  class  of 
enamels  used  for  staining  teeth  in  imitation  of  the  dark  spots  on  the 
cutting  edges  of  much-worn  incisors  and  cuspids  of  middle-aged  and 
elderly  patients,  and  for  reproducing  in  the  porcelain  teeth  the  discolor- 
ation incident  to  devitalization  of  the  natural  organs,  etc.  These  are 
usually  the  darkest  shades  of  brown  and  olive. 

Enamels  are  mixed  with  clean  water  until  the  mixture  presents  a 
cream-like  appearance.  They  are  then  applied  with  camePs-hair  pen- 
cils of  different  sizes.  The  first  layer  is  placed  on  the  necks  of  the 
teeth,  extending  to  near  the  cutting  edge,  tapering  in  quantity  as  it 
approaches  the  point.  In  applying  the  enamel  the  block  is  held  gum 
upward,  care  being  taken  that  the  enamel  adheres  to  the  body,  and,  if 
any  creases  occur,  to  wet  them  down  by  touching  them  with  a  wet 
camel's-hair  brush,  and  that  all  ridges  be  smoothed  or  trimmed  down 
with  the  small  carving  knife. 

When  the  point  enamel  is  applied  the  block  should  be  reversed,  so  as 
to  be  held  with  the  teeth  upward.  The  brush  is  partly  filled  with  the 
point  enamel,  and  applied  lightly  to  the  cutting  edges  of  the  teeth  to  the 
thickness  of  about  a^th  of  an  inch,  and  carefully  worked  down  with  a 
full  brush  in  the  direction  of  the  neck  of  each  tooth.  All  the  neck 
enamel  previously  laid  on  must  be  quite  covered,  but  the  point  enamel 
should  be  applied  very  sparingly  as  it  approaches  the  margin  of  the  gum, 
full  thickness  being  given  at  the  cutting  edge  only. 

Some  experience  is  required  in  laying  on  the  point  enamel  to  avoid 


CARVING   BLOCK  TEETH.  239 

wiping  off  the  neck  enamel  at  the  same  time.  It  is  desirable  that  the 
latter  should  show  through  the  thin  layer  of  the  former  and  be  toned 
and  blended  by  it.  To  prevent  mixing  of  the  two  enamels,  and  the 
consequent  injury  to  the  effect  of  each,  the  brush  full  of  enamel  should 
be  drawn  lightly  over  the  teeth  in  a  manner  to  allow  the  enamel  to  be 
drawn  from  off  the  point  of  the  brush  upon  the  block.  The  edges  may 
be  made  even  by  touching  them  with  a  wet  camel's-hair  brush.  It  is 
essential  that  the  enamel  be  carried  well  between  the  teeth. 

After  completing  the  enamelling,  the  carving  and  shaping  is  begun 
by  separating  the  teeth  from  each  other  with  the  string  bow.  The  con- 
tour is  now  carefully  formed,  the  separations  at  the  necks  being  made  by 
cutting  inverted  A-shaped  spaces  between  them.  The  block  is  again 
reversed  with  the  cutting  edges  down,  and  the  necks  given  distinctness 
by  well-directed  sweeps  of  the  knife  to  form  the  semicircular  lines 
between  the  necks  and  the  gum.  The  faces  of  the  teeth  are  then  given 
the  character  of  the  type  which  they  are  designed  to  imitate. 

It  must  be  remembered  that  the  tendency  of  the  vitrefying  process 
is  to  flatten  down  prominences  and  to  round  off  corners ;  therefore  all 
the  features  and  outlines  of  the  teeth  should  be  somewhat  exaggerated, 
so  that  the  finished  block  may  retain  the  requisite  degree  of  individu- 
ality. 

Forming  the  contour  of  the  teeth  from  the  neck  to  the  point  is  the 
most  important  part  of  the  operation  of  carving,  and  the  style  of  teeth 
needed  for  the  case  in  hand  will  depend  upon  the  amount  of  prominence 
given  the  enamelled  block.  With  a  definite  model  in  mind  the  carver 
must  take  into  consideration  and  anticipate  all  the  changes  incident  to 
the  burning  process. 

Some  well-thought-out  systematic  plan  for  carving  teeth,  and  one  that 
will  include  the  general  characteristics  of  the  natural  teeth,  will  be  found 
of  great  convenience,  so  that  close  imitations  may  be  obtained.  A  small, 
well-selected  collection  of  natural  teeth  should  be  made,  such  as  will 
serve  the  purpose  to  show  the  wide  ranges  of  sizes  and  shapes  existing 
in  the  natural  organs. 

Gum  Enamel. — This  enamel  requires  in  mixing  at  least  20  grains  of 
gum  arable  to  the  ounce  of  enamel  to  prevent  it  from  settling  to  the  bot- 
tom of  the  cup  on  account  of  its  greater  coarseness.  It  is  first  applied  to 
the  festoons  between  the  teeth  with  the  point  of  the  carving  knife ;  the 
rest  is  easily  put  on  with  the  brush,  care  being  taken  to  carry  it  close  to 
the  necks  of  the  teeth,  but  not  to  allow  it  to  overlap  the  necks.  It  is 
not  necessary  to  lay  the  gum  enamel  on  very  smoothly ;  the  result  will 
be  better  if  left  rough  and  somewhat  uneven  :  fusing  at  a  lower  tempera- 
ture than  the  point  enamels,  it  will  take  care  of  itself  in  burning,  and  a 
moderate  degree  of  unevenness  of  surface  tends  to  produce  a  natural 
effect  in  the  finished  block. 

The  gumming  process  in  carved  work  is,  as  a  rule,  poorly  done.  It  is 
not  always  recognized  that  the  surface  of  the  natural  gums  have  cha- 
racteristic irregularities  and  variations  in  degrees  of  shade  and  color. 
The  ridges  around  the  necks  of  the  teeth  should  be  carefully  imitated. 
The  shade  of  the  gum  is  a  little  deeper  between  the  teeth  than  immedi- 
ately over  the  roots  :    this  should  not  be  overlooked. 

The  palatal  surfaces  of  the  teeth  and  inner  surfaces  of  the  blocks 


240 


MOULDING   AND   CARVING  PORCELAIN  TEETH. 


should  be  given  a  thin  layer  of  point  enamel  to  serve  as  a  glazing  to  the 
rough  surface  of  the  body,  after  which  the  blocks  are  ready  for  burning, 
and  should  be  allowed  to  dry  perfectly  for  that  purpose. 
(Figs.  274  and  275  show  a  finished  front  block.) 


Fig.  274. 


Fig.  275. 


Labial  side  ol  flnislnd  block. 


Lingual  side  of  finished  block. 


If  the  teeth  are  long,  and  it  is  desirable  to  maintain  close  contact 
between  centrals,  difficulty  may  be  encountered  in  preventing  "  spread- 


FiG.  276. 


Fig.  27'J 


ing"  while  burning.    This  may  be  prevented  by  tying  the  teeth  together 
with  a  loop  of  body  placed  across  the  separations  from  one  tooth  to 

another.  It  is  done  by  mixing  some 
body  with  water,  so  that  it  can  be  ap- 
plied with  a  small  brush.  After  the  teeth 
are  burned  the  loop  of  body  can  be 
ground  away  with  the  corundum  wheel. 
Fig.  276,  A,  shows  the  spreading  as  it 
often  occurs  during  the  burning  of  a  block 
not  so  reinforced  ;  Fig.  276,  B,  shows  the 
manner  of  arranging  the  body  to  prevent 
spreading ;  Fig.  276,  C,  shows  block  from  same  mould  in  which  no  change 
has  occurred  in  consequence  of  the  reinforcement  of  body  on  inside. 

White,  opaque  spots  are  frequently  seen  on  natural  teeth  :  these  may 
be  imitated  with  an  enamel  of  the  following  proportions : 


An  example  ot  "sprawling 


Opaque  E'namel 
Kaolin, 
Feldspar, 


■k  oz. 


Mix  well. 


Before  burning  small  depressions  are  cut  in  the  soft  enamel  and  filled 
evenly  with  the  opaque  enamel. 

Staining  Teeth. — To  closely  imitate  certain  peculiarities  of  the 
natural  organs  it  is  sometimes  desirable  to  stain  their  cutting  edges  to 
represent  the  dark-brown  dentine  often  noticed  betM^een  the  outer  and 
inner  plates  of  enamel  in  the  much-worn  teeth  of  middle-aged  men  who 


CARVING   BLOCK  TEETH. 


241 


have  used  tobacco ;  or,  again,  to  occasionally  darken  a  tooth  in  imitation 
of  the  color  of  teeth  in  which  the  pulps  have  died.  The  following  for- 
mulae may  be  used  Avhere  properly  indicated : 


Dark-greeniiih  Stain :  Platinum  sponge, 
Titanium  oxide, 
Feldspar, 
Enamel  tlux, 

Dark-yellow  Slain :      Titanium  oxide. 
Gum  frit, 
Enamel  flux, 


Black  Stain  : 


Iron  scale, 
Feldspar, 


5gr. 
10  " 
10    " 

2   " 

20  gr. 

4  " 

2   " 

10  gr. 

5  dwt. 


These  stains,  like  the  otlier  enamel  frits,  vary  in  depth  according  to 
the  state  of  fine  division  attained  ;  they  should  be  kept  in  small  glass 
jars,  with  fused  trials  fastened  outside  for  reference. 

Cavities  for  filling  may  be  cut  with  excavators  in  the  biscuited  teeth. 
As  a  rule,  cavities  for  filling  in  artificial  teeth  are  objectionable.  Occasion- 
ally, however,  a  patient  loses  a  tooth  which  has  been  conspicuously  filled 
with  gold  for  a  number  of  years :  in  such  instances  its  replacement 
by  an  ordinary  tooth  might  constitute  so  noticeable  a  change  as  to  war- 
rant the  attempt  to  imitate  the  filled  natural  tooth. 

Other  methods  have  been  devised  to  produce  block  teeth  for  special 
cases  with  less  expenditure  of  time,  and  to  avoid  the  liability  to  accident 
so  common  in  the  plan  just  described.  In  the  various  processes  sug- 
gested the  tendency  has  been  to  adopt  some  plan  of  moulding  instead  of 
carving,  and  to  make  the  work  more  a  mechanical  procedure  than  one 
which  requires  a  high  degree  of  artistic  talent. 

Fig.  278. 


Biscuited  teeth. 

In  one  process  biscuited  plain  teeth  were  placed  in  position  while  the 
body  was  soft  (Fig.  278  gives  front  and  side  views  of  the  forms  of  bis- 
cuited teeth  designed  for  this  purpose),  but  this  plan  has  been  abandoned 
on  account  of  the  frequent  failure  of  the  partly  burned  teeth  to  unite 
with  the  soft  body,  which  was  often  only  apparent  after  the  teeth  were 
burned. 

Another  process  consists  in  making    movable  matrices  of  different 

sizes  and  styles  to  correspond  to  the  classes  of  teeth  described  in  this 

chapter,  the  object  being  to  do  the  enamelling  and  moulding  of  the  entire 

block  in  one  operation.     These  matrices  are  made  of  very   thin  sheet 

ifi 


242 


MOULDING  AND   CARVING   PORCELAIN  TEETH. 


brass,  about  No.  32,  stamped  over  hard  brass  or  steel  dies  :    the  die 
must    necessarily    be    an    accurate    copy    of   the    teeth    desired,    with 


Fig.  279. 


Enamel  cups. 

allowance    for    shrinkage    and    other    changes    incident    to    burning. 
These   cups   are    arranged    on    the   wax    articulator    precisely   in   the 

position  required  in  the  finished 
Fig.  280.  block.     Walls  of  plaster  are  then 

made  in  the  manner  described  on 
page  232.  When  hard  enough  the 
walls  are  removed,  bringing  with 
them  the  brass  enamel  cups,  as 
shown  in  Fig.  279. 

The  gum  surfaces  of  the  walls 
are  then  lined  with  tin-foil ;  the 
enamel  cups  are  to  be  made  fast, 
should  any  become  detached  from 
the  wall,  by  means  of  hot  wax  or 
resin  and  wax  cement.  The 
cups  and  walls  are  then  oiled, 
the  enamel  is  placed  in  the  cups, 
point  enamel  first,  and  then  the 
base.  The  body  is  applied  the 
same  as  in  ordinary  carved  work 
(Fig.  280). 

The  heat  of  a  small  spirit  lamp 
is  applied  until  the  body  is  dry 
(enough  and  the  wax  or  cement  sufficiently  softened  to  admit  of  the 
removal  of  the  wall.  The  cups  will  be  found  adhering  to  the  block  : 
these  must  be  removed  without  injury  to  the  moulded  teeth.  Dr.  W.  R. 
Hall,  to  whom  is  due  the  credit  of  devising  this  method,  found  the  dif- 
ficulties of  making  the  dies  and  forming  the  cups  very  great,  the  very 
large  munber  of  the  latter  needed  for  a  working  set,  over  a  thousand 
being  required,  complicating  instead  of  simplifying  the  production  of 
block  teeth.     On  the  other  hand,  the  method  possesses  the  advantages 


Brass  cups  in  position  for  moulding. 


CARVING  BLOCK  TEETH. 


243 


over  carved  work  of  affording  more  perfect  and  finished  teeth,  greater 
facility  in  their  duplication,  less  liability  to  accidents,  superior  density, 
and  uniformity  of  distribution  of  the  enamels. 

Brass  Moulds  for  Porcelain  Teeth. — Mould-making  is  generally 
thought  to  require  peculiar  talents  and  a  high  degree  of  mechanical  skill. 
It  certainly  does  demand  artistic  talent,  but  the  mechanical  part  of  it  is 
not  particularly  difficult.  It  includes  the  carving  of  the  plaster  blocks, 
making  the  plaster  pattern  of  the  mould,  casting  it  in  hard  brass  or 
bronze,  and  the  "  cutting "  or  finishing  of  the  mould. 

The  plaster  blocks  constitute  the  design,  and  are  a  complete  set  of 
block  teeth  carved  in  plaster,  with  allowance  made  for  shrinkage  and 
other  changes  which  take  place  in  the  vitrefying  process.  This  part  of 
the  work  must  be  done  by  an  artist  and  one  who  has  knowledge  of  the 
several  classes  of  human  teeth.  These  designs  should  always  be  made 
from  natural  teeth,  but  the  custom  amongst  manufacturers  is  to  use 
plaster  face-blanks,  made  from  plain  teeth  moulds,  somewhat  larger 
than  is  needed  for  the  set  to  be  made,  to  allow  for  carving  to  the  proper 
size  and  shape.  The  blanks  are  arranged  on  a  rim  of  wax  similar  to 
articulating  wax  ;  the  gums  are  formed  of  paraffin  or  the  pink  combina- 
tion of  paraffin  and  wax  ;  broad  spaces  are  left  between  the  centrals  ; 
the  cuspid  and  first  bicuspids  and  the  second  bicuspids  and  first  molars, 
as  sectional  blocks  for  an  entire  upper  denture,  are  divided  into  six 
pieces.  Each  block  must  be  provided  with  a  slight  excess  of  material 
at  the  joint,  to  afford  sufficient  latitude  in  fitting  them  together.  A  wall 
of  plaster  about  one-fourth  of  an  inch  in  thickness  is  run  on  the  outside 
of  the  model,  so  as  to  include  the  entire  set  of  blanks  :  when  hard  enough 
it  is  trimmed  so  as  not  to  exceed  in  height  the  cutting  edges  of  the  tooth 
blanks,   varnished,  and    oiled ;  an 

inside  wall  is  then  made  of  plaster  of  Fig.  281. 

the  same  height  as  the  outside  one. 
The  inside  wall  is  removed  when 
hard  in  one  piece ;  the  outside  one  is 
cut  into  six  pieces  with  a  thin  saw- 
blade,  the  cut  being  made  between 
the  centrals,  the  cuspids  and  bicus- 
pids, and  the  bicuspids  and  molars 
at  the  spaces  shown  in  Fig.  281. 
The  sections  thus  made  arc  then 
separated  from  the  model. 

Both  the  outside  and  inside  walls 
are  trimmed,  varnished,  and  laid 
aside  to  dry.  The  removal  of  the 
blanks  from  the  model  is  next  in 
order,  and  both  walls  are  given  a 
coating  of  shellac  varnish.  Fig. 
282  shows  the  walls  made  for  a 
lower  set  of  plaster  blocks.  The 
walls  are  now  to  be  placed  on  the 
model  and  secured  in  position  with 

twine  or  wire  :  they  are  then  oiled,  and  plaster  mixed  to  the  consist- 
ence of  cream    is   first  painted  over  the    surface,    as  representing   the 


Tooth-blanks  arranged  on  cast. 


244 


MOULDING   AND   CARVING   PORCELAIN  TEETH. 


teeth,  with  a  camel's-hair  brush,  when  the  residue  is  run  in  between 
the  inside  and  outside  walls  and  allowed  to  set  thoroughly  before 
removal.  If  the  plaster  has  been  carried  into  all  depressions  and  inter- 
stices between  the  walls,  a  continuous  set  of  plaster  blocks  will  be  the 
result.     These  are  separated  into  six  sections  by  means  of  a  thin  saw- 


FiG.  282. 


View  of  the  walls  and  cast,  separated. 

blade,  as  shown  in  Fig.  282,  the  six  front  teeth  in  two  sections  of  three 
each,  the  first  and  second  bicuspids  of  each  side  in  two  other  sections  ; 
the  molars  are  divided  in  the  same  way.  These  plaster  blocks  now 
require  trimming  on  the  inside,  the  carving  of  the  masticating  surfaces 
of  the  bicuspids  and  molars  in  imitation  of  the  natural  organs,  and  the 
cutting  of  a  recess  for  the  pins,  as  seen  in  Fig.  283. 

The  ends  of  the  blocks,  or  those  parts  technically  called  the  joints,  must 
be  trimmed  so  that  they  will  taper  sufficiently  to  ensure  their  safe  de- 
livery from  the  plaster  mould,  as  shown  by  the  pin  sides  of  the  plaster 
blocks  in  Fig.  283.  If  not  properly  bevelled  at  all  points,  so  that  no 
undue  retention  will  occur,  it  may  be  necessary  to  remove  the  pattern 


CARVING  BLOCK  TEETH. 


245 


blocks  piecemeal.     The  plan  of  such  a  mould  would  then  be  found  to  be 
defective,  and,  as  may  readily  be  surmised,  it  vyould  not  be  possible  to 


Fig.  283. 


Plaster  blocks,  finished. 

obtain  a  brass  mould  from  a  pattern  in  which  so  serious  a  fault  existed. 
After  these  details  have  received  careful  attention  and  the  blocks  have 
been  trimmed  and  carved  to  the  satisfaction  of  the  workman,  they  should 
receive  at  least  two  coats  of  shellac  or  sandarac  varnish. 

The  Plaster  Mould. — The  preparation  of  the  plaster  mould  is  the 
second  part  of  the  process  of  mould-making,  the  first  part  being  the 
modelling  of  the  designs  in  the  form  of  plaster  blocks.  These  designs 
are  really  the  foundation  of  the  whole  system,  and  require  in  their  pro- 
duction artistic  talent  and  knowledge  of  the  forms  of  the  different  types 
of  human  teeth.  With  the  exception  of  the  cutting  or  finishing  of  the 
brass  mould,  the  rest  of  the  process  is  purely  mechanical,  but  the  carving 

Fig.  284. 


Foundation  plate. 

of  the  models  and  the  finishing  of  the  face  sides  of  the  brass  moulds 
should  be  done  by  the  same  hands.     The  mechanic  to  whom  this  part 


246 


MOULDING   AND   CARVING  PORCELAIN  TEETH. 


of  the  work  is  usually  entrusted  is  liable  to  cut  out  many  of  the  lines 
and  depressions  observed  in  the  natural  teeth  and  imitated  in  the  plaster 
models. 

By  referring  to  Figs.  288  and  289  it  will  be  seen  that  the  finished 
mould  consists  of  five  pieces — the  face  side,  the  pin  side,  two  end-  or 
crown-pieces,  and  a  key-piece.  These  pieces  have  all  to  be  made  in 
plaster  to  serve  as  patterns  from  which  to  cast  facsimiles  in  brass.  The 
plaster  blocks  are  arranged  on  a  foundation  plate.  This  plate  can  be 
made  of  brass  or  zinc,  as  shown  in  Fig.  284,  6^  inches  long,  3  inches 
wide,  and  J  of  an  inch  thick,  with  oblong  recesses  to  receive  the  blocks — 
those  for  the  front  blocks  1  inch  long  and  J  an  inch  wide ;  those  for 
the  bicuspids,  f  of  an  inch  long  and  J  an  inch  wide ;  and  those  for  the 
molars,  ^  of  an  inch  long  and  ^  an  inch  wide.  The  black  lines  on  the 
plate  are  used  as  guides  to  measure  from  in  placing  the  blocks;  the  round 
holes  at  the  ends  are  to  receive  the  pins  seen  on  the  frames  in  Fig.  285. 

The  plaster  blocks  are  placed  on  the  foundation  plate  faces  upward, 
wdth  the  cutting  edges  opposite  to  each  other,  as  seen  in  Fig.  286,  and 
are  then  secured  in  position  with  beeswax,  clay,  or  putty,  which  also 
marks  the  correct  line  of  division  between  the  two  halves  of  the  mould. 
This  is  a  very  important  detail  of  mould-making ;  upon  its  correct  man- 
agement depend  the  successful  application  of  the  enamels  and  the  safe 
delivery  of  the  moulded  porcelain  blocks.  This  line  of  division  should 
extend  along  the  middle  of  the  cutting  edges  of  the  incisors  and  canines 
and  the  gum  edge,  but  should  include  but  little  of  that  portion  of  the 
block  called  the  joint.  By  referring  to  Fig.  207  the  reader  will  see  that 
the  face  side  of  the  mould  gives  merely  the  distinct  outline  of  the  entire 
face  of  the  block,  and  that  the  bulk  of  the  block  is  represented  in  the 
pin  side ;  yet  the  edges  of  the  face  side  of  the  blocks  should  be  sufiiciently 


Fig.  285. 


Brass  frame. 


well  defined  to  assist  in  holding  the  enamels  in  position  when  the  mould 
is  pressed  together.     The  front  blocks  are  secured  to  the  plate  two  six- 


CARVING  BLOCK  TEETH. 


247 


teenths  of  an  inch  from  its  centre  line ;  the  bicnspitl  blocks,  three- 
sixteenths  of  an  inch  from  the  line ;  the  molar  blocks,  four-sixteenths 
from  the  line.  The  side  blocks  are  arranged  farther  apart  at  the  end 
near  the  molars  than  at  the  other,  to  allow  for  a  tapering  key,  as 
shown  by  C  in  Fig.  289.  If  all  spaces  between  the  block  and  the  foun- 
dation plate  have  been  stopped  with  clay  or  putty,  the  ])late  with  arranged 
blocks  is  ready  for  the  frame. 

The  frame  is  in  two  sections  made  of  polished  brass,  one  section  made 
to  articulate  with  the  other  by  means  of  pins  and  corresponding  holes,  as 
seen  in  Fig,  285.  The  inside  tapers  so  that  the  plaster  mould  when  hard 
may  deliver  without  difficulty.  Tliese  frames  measure  4f  inches  in  length 
and  2f  inches  in  width,  each  section  being  f  of  an  inch  high  with  a 
thickness  of  ^  of  an  inch.  The  part  with  pins  is  well  oiled  on  its  inside 
and  placed  on  the  plate.  The  plaster  blocks  having  been  oiled,  the  plaster 
is  mixed  by  dropping  it  into  water  and  allowing  it  to  settle  without  stir- 
ring, so  as  to  exclude  air ;  the  excess  of  water  is  then  poured  off;  the 
blocks  carefully  coated  with  thin  plaster  by  means  of  a  small  camel's-hair 
pencil ;  the  rest  of  the  plaster  is  then  poured  in  and  levelled  off  even 
with  the  top  of  the  frame  with  a  spatula.  When  the  plaster  becomes  hard 
the  plate  is  removed  and  the  face  side  of  the  pattern  is  secured. 

The  blocks  are  then  carefully  taken  from  the  face  side  of  the  plaster 
mould,  and,  if  any  of  the  edges  are  broken,  they  must  be  repaired  with 
wax  or  plaster  and  made  smooth.  After  the  removal  of  the  blocks  the 
mould  must  be  varnished  with  shellac  or  sandarac  and  allowed  to  dry 
thoroughly,  when  the  blocks  are  replaced.  The  space  between  the 
bicuspid  and  molar  blocks  is  filled  by  a  piece  of  wax,  as  seen  in  Fig. 
286,  to  form  the  depression  intended  for  the  end-pieces  and  key  in  the 


Fig.  286. 


Pin  side  of  plaster  mould,  witVi  plaster  blucks  and  wax  in  position. 

pin  side  of  the  mould.  The  whole  fixture  is  then  thoroughly  saturated 
in  clean  water,  the  surfaces  coated  lightly  with  oil,  and  the  other  section 
of  the  brass  frame  placed  in  ])osition  and  filled  with  plaster  mixed  and 
applied  in  the  manner  previously  described  :  this  forms  the  pin  side  of 
the  mould.  The  two  sections  are  easily  separated  when  the  plaster  has 
hardened  sufficiently  by  introducing  a  knife-blade  between  them  and 
carefully  prying  apart.  The  plaster  blocks  will  usually  be  found  in  the 
pin  side  of  the  mould,  because  the  greater  portion  of  the  block  is 
embraced  in   that  part  of  it,  and   consequently  offers  more  surface  for 


248 


MOULDING   AND   CARVING   PORCELAIN  TEETH. 


retention  than  does  the  face  side.  The  brass  frames  are  next  to  be 
removed  from  each  part  of  the  plaster  mould  by  tapping  the  former 
gently  with  a  small  wooden  mallet.  The  blocks  are  then  to  be  removed 
from  the  pin  side  of  the  mould  :  this  must  be  done  with  the  greatest  care 
by  inserting  a  sharp  excavator  or  knife-point  under  the  block  and  gently 
prying  it  out.  If  any  part  of  the  mould  is  broken  and  carried  away 
with  either  of  the  blocks,  the  piece  may  be  fastened  back  to  its  proper 
place  with  thick  shellac  varnish,  or,  if  lost,  the  defect  may  be  repaired 
with  beeswax. 

The  crowns  or  masticating  surfaces  of  the  bicuspids  and  molars  are 
formed  by  end-pieces  held  in  place  by  a  wedge-shaped  piece  of  brass, 
as  shown  by  A,  B,  and  C,  Fig.  289.  The  wax  seen  in  Fig.  286  must 
be  taken  away  from  between  the  side  blocks,  and  the  blocks  removed 
and  carefully  cleaned ;  the  space  formed  by  this  piece  of  wax  must  be 
trimmed  so  as  to  increase  its  width  about  three-sixteenths  of  an  inch, 
its  floor  made  perfectly  flat  and  its  sides  perpendicular,  and  arranged  to 
taper  toward  the  end  nearest  the  front  blocks,  where  it  should  be  slightly 
narrower  than  at  the  molar  end  of  the  space.  This  space  at  its  floor  and 
sides  must  be  level  and  true,  or  the  crown-pieces  and  key  A,  B,  C 
(Fig.  290)  will  not  fit  well  in  the  finished  mould  :  the  surface  of  the 

Fig.  '2^1 


Face  side  of  plaster  mould,  with  temporary  key. 

recess  is  then  varnished.  A  temporary  key  of  brass  is  placed  midway 
in  this  space  and  secured  with  wax,  as  shown  in  Fig.  287,  and  allowed 
to  extend  a  quarter  of  an  inch  beyond  the  end  of  the  mould.  The 
plaster  mould  is  then  oiled  and  put  in  w^ater  to  drive  out  the  air  ;  the 
side  blocks  are  oiled  and  put  in  place ;  the  face  side  of  the  mould  is 
oiled  and  put  in  position,  and  the  two  sides  tied  together.  Plaster, 
mixed  thin,  is  then  run  into  the  spaces  on  each  side  of  the  temporary 
key  extending  beyond  the  mould  to  the  end  of  the  key.  After  the 
plaster  is  hard  the  temporary  key  is  carefully  drawn  out  by  means  of 
pliers,  when  the  crown-pieces  may  be  easily  removed.  All  the  parts  of 
the  plaster  mould  are  now  to  be  thoroughly  dried  by  gentle  heat ;  grooves 
are  then  cut  around  each  block  in  both  sides  of  the  mould  to  allow  for 
the  escape  of  the  excess  of  body  and  enamel  usual  in  moulding  teeth. 
All  parts  of  the  plaster  mould  must  be  made  as  smooth  and  perfect  as 
possible,  as  its  condition,  whether  good  or  bad,  is  duplicated  in  the  brass 
castings,  where  it  is  much  more  difficult  to  correct  imperfections  or  faults 


CARVING   BLOCK  TEETH. 


249 


than  in  the  plaster.     When  entirely  finished  and  thoroughly  dried  all 
the  parts  of  the  plaster  mould  are  to  be  varnished  with  shellac  and 


Fig.  288. 


Face  side  of  brass  mould. 


allowed  to  dry  thoroughly,   when  they  are   ready  to  be  sent  to  the 
foundry  to  be  cast  in  hard  brass. 


Fig.  289. 


Pm  side  of  brass  mould 


Fig.  288  shows  the  face  side  of  the  finished  brass  mould.     Fig.  289 
shows  the  pin  side,  A  and  B  the  crown-piece,  C  the  key.     Retaining 


Fig.  290. 


Crown-piece. 


pins  of  brass  are  put  in  to  prevent  movement  of  the  crown-piece  during 
moulding  :  the  heads  of  these  are  seen  in  Fig.  289  between  the  molar 
and  bicuspid  blocks. 


250 


MOULDING  AND   CARVING   PORCELAIN  TEETH. 


Cutting-  and  Finishing  Brass  Moulds. — Undoubtedly,  moulded 
teeth  afford  opportunities  for  better  results  in  the  imitation  of  the 
natural  organs  than  does  carving,  but  the  original  designs,  as  well  as  the 
cutting  and  finishing  of  the  moulds,  must  be  executed  by  a  higher  class 
of  workmen  than  have  as  yet  been  entrusted  with  that  exceedingly 
artistic  work.  Much  of  the  work  of  the  mould-maker  is  apparently 
done  rather  from  habit  than  through  any  clear  insight  into  the  actual 
requirements  of  his  task.  The  horizontal  depressions  on  the  faces  of 
the  central  and  lateral  incisors  are  usually  too  stiff  and  distinctly  defined, 
while  their  lines  are  straight  and  unnatural.  These,  however,  are  de- 
fects of  execution  rather  than  of  the  system  of  mould-production,  and 
will  doubtless  eventually  be  remedied. 

The  tools  required  in  mould-finishing  are  comprised  in  the  following 
list:  Two  or  three  flat  files,  10  or  12  inches  long,  bastard  and  smooth- 
cut,  for  finishing  the  outside  of  the  mould ;  small  files,  flat  and  half- 
round,  for  the  inside ;  a  half-dozen  gravers,  such  as  are  used  by  wood- 
engravers,  flat  and  round-edged,  of  the  different  sizes  shown  in  Fig. 
291  ;   a  bench-vise  with  jaws  about  3  inches  wide ;   an  upright  breast- 

FiG.  291. 


Gravers,  of  Stub's  steel. 


drill,  with  three  sizes  of  Morse  drills  for  adjusting  the  guiding  pins ; 
taps  and  dies  for  the  same  ;  two  pairs  of  steel  dividers ;  a  pair  of  steel 
callipers ;  a  steel  square,  4  inches  long,  for  truing  up  the  mould ;  a  hack 
saw,  for  sawing  off  the  pins ;  a  steel  clamp,  to  hold  the  two  sides  of  the 
mould  together  when  drilling  the  holes  ;  a  30-pound  anvil ;  a  4-pound 
hammer ;  a  taper  reamer  for  the  guiding  pin-holes. 

An  unskilful  workman  can  do  much  harm  to  the  brass  mould  in  the 
cutting  and  finishing.  The  graver  should  not  be  used  to  change  the 
contour  or  lines  of  the  teeth  :  any  good  founder  can  reproduce  all  the 
parts  of  the  plaster  mould  in  brass  in  so  nearly  a  perfect  condition  that 
the  gravers  will  be  needed  only  to  finish  the  surface  of  the  mould,  but 
not  to  change  it.  Brass  or  bronze,  like  other  hard  metals,  when  cast 
will  shrink  somewhat,  and  thus  the  brass  casting  becomes  smaller 
than  the  plaster  model  of  which  it  is  a  facsimile  :  in  finishing  the  sur- 
face of  the  depressed  teeth  and  gums  in  the  brass  mould  the  workman 
will  necessarily  enlarge  to  some  extent  the  reversed  representation 
of  the  blocks  to  the  original  size  of  the  plaster  models,  and  the  work 
should  be  done  with  such  precision  that  the  latter  can  be  placed  in  the 
brass  mould  and  fit  as  though  they  had  been  moulded  in  it. 


CARVING  BLOCK  TEETH.  251 

A  hard  bronze,  containing  about  15  per  cent,  of  tin,  is  better  adapted 
for  moulds  than  is  ordinary  brass,  as  it  affords  a  sharper  casting  and  the 
requisite  degree  of  hardness  to  prevent  the  moukl  from  yielding  when 
exposed  to  heavy  pressure.  When  the  castings  are  received  from  the 
foundry  it  will  be  seen  that  the  edges  along  the  line  of  division  of  the 
blocks  on  the  face  and  pin  sides  of  the  mould  do  not  touch  when  these 
two  parts  are  placed  together :  this  is  due  to  the  unequal  contraction  of 
the  metal,  and  must  be  corrected  by  filing  down  the  high  parts,  so  that 
all  edges  will  meet  and  the  two  halves  of  the  mould  fit  together  without 
rocking. 

After  fitting  together  the  two  sides  of  the  mould,  trial  blocks  of 
plaster  should  be  made,  to  ascertain  if  the  outlines  of  the  blocks  meet 
properly.  The  trial  blocks,  made  by  pressing  plaster  between  the  two 
halves  of  the  mould,  will  indicate  any  defect  in  adjustment.  If,  how- 
ever, it  is  found  that  the  outline  edges  are  quite  together,  and  that  the 
relation  of  one  half  to  the  other  is  correct,  the  guide  pins  are  to  be  put 
in,  in  order  that  the  relation  of  the  parts  be  permanently  fixed.  This  is 
done  by  firmly  holding  the  two  parts  of  the  mould  in  a  steel  clamp,  and 
then  drilling  the  holes  for  the  pins  entirely  through  each  side  with  a 
three-sixteenths  of  an  inch  drill.  One  of  the  guide  pins  is  placed  in  the 
face  side  of  the  mould  opposite  the  right  central,  the  other  in  the  pin 
side  opposite  the  left  molar.  They  must  be  permanently  screwed,  one 
in  each  side  of  the  mould,  as  shown  in  Figs.  288  and  289.  After  the 
holes  are  drilled,  the  one  in  the  face  side  opposite  the  central  and  the 
one  in  the  pin  side  opposite  the  left  molar  must  be  screw-tapped  to 
receive  the  screw  end  of  the  guide  pins ;  the  other  end  of  the  pins  must 
taper  slightly  near  its  extremely  so  as  to  freely  enter  the  hole  opposite  to 
it ;  but  the  pins  must  fit  close  enough  to  prevent  lateral  movement  when 
the  two  parts  of  the  mould  are  quite  together.  These  pins  should  be 
made  of  steel  wire  not  less  than  three-sixteentlis  of  an  inch  in  thickness. 
The  outside  of  the  mould  is  then  to  be  squared  and  finished  :  this  may 
be  done  either  in  a  lathe  or  by  filing  guided  by  the  try-square  and  cal- 
lipers, for  it  is  very  important  that  the  mould  when  the  two  parts  are 
together  should  be  uniform  in  thickness  and  perfectly  level,  as  there  is 
danger  if  these  conditions  are  not  secured  of  its  being  sprung  out  of 
shape  by  the  press  in  moulding  teeth. 

The  next  step  toward  the  completion  of  the  mould  is  the  fitting  of 
the  end-pieces  in  the  space  between  the  back  blocks :  the  floor  of  the 
space  must  be  filed  perfectly  flat  and  level,  and  the  side  made  perpendic- 
ular ;  the  crown-pieces  where  they  are  in  contact  with  the  key  are  made 
smooth  and  true ;  the  taper  key,  C  (Fig.  290),  is  made  to  fit  between 
them  and  holds  the  crown-pieces  securely  against  the  perpendicular  walls 
of  the  space  alluded  to  above  during  the  operation  of  moulding  teeth. 
This  key  is  made  longer  than  the  crown-pieces,  so  that  it  can  be  driven 
between  them  with  a  wooden  mallet  to  facilitate  its  removal.  To  prevent 
the  crown-pieces  from  sliding  back  while  the  mould  is  under  pressure, 
two  brass-headed  pins  are  riveted  in  the  pin  side  of  the  mould  between 
the  bicuspid  and  molar  block,  as  shown  in  Fig.  289,  the  pin  being  partly 
in  the  mould  and  partly  in  the  crown-pieces. 

The  cutting  and  smoothing  of  the  gums  and  faces  of  the  teeth  in  tlie 
castings  is  not,  as  is  generally  believed,  a  very  difficult  mechanical  ope- 


252  MOULDING  AND   CARVING   PORCELAIN   TEETH. 

ration  ;  it  does,  however,  require  artistic  skill  and  judgment.  The  fine 
lines  of  the  plaster  pattern  are  made  less  distinct  by  the  casting  of  the 
metal.  The  gravers  are  to  be  employed  to  restore  the  definiteness  of 
outline  and  contour,  and  great  care  must  be  taken  in  doing  this  to  avoid 
change  or  obliteration  of  the  characteristic  features  of  the  original  pat- 
tern. The  gravers  should  be  of  the  best  quality  of  steel  tempered  to  a 
straw  color ;  they  must  be  kept  ground  to  a  long  bevel  and  a  keen  edge, 
the  latter  being  made  by  means  of  an  Arkansas  stone  :  the  gouge-shaped 
graver  is  used  at  first  to  cut  a  clean  and  smooth  surface  on  the  part  of 
the  mould  reprCvSenting  the  faces  of  the  front  teeth.  A  plaster  set  of 
teeth  should  then  be  made,  Avhich,  on  comparison  with  the  original  pat- 
terns, will  indicate  that  further  cutting  is  needed  to  bring  the  mould  to 
correspond  exactly  Math  them.  The  pin  side  of  the  mould  will  require 
trimming  with  the  flat  or  chisel-shaped  graver  to  give  it  a  smooth  sur- 
face, and  to  bring  the  size  to  that  of  the  original  pattern,  which  should 
fit  perfectly  into  the  brass  mould  as  though  it  had  been  moulded  there ; 
and  this  is  a  good  test  for  the  accuracy  of  the  brass  casting. 

During  the  cutting  repeated  trials  should  be  made  with  plaster  to  see 
if  the  edges  come  properly  together  with  no  overlapping  ;  and  as  the  cut- 
ting proceeds  it  will  be  necessary  for  the  workman  to  frequently  see  the 
reverse  aspect  of  the  teeth  :  this  he  does  witli  black  try-wax,  which  is  made 
by  mixing  beeswax  and  lampblack  with  a  few  drops  of  turpentine.  Small 
pieces  of  this  wax  are  held  in  the  hand  while  cutting,  the  warmth  of  the 
hand  being  sufficient  to  soften  it :  in  this  way  the  mould-maker  is  able 
to  take  impressions  of  the  concavities  of  the  teeth  as  the  work  proceeds. 
Care  is  required  in  carving  the  original  patterns  to  form  the  margins 
aronnd  the  necks  of  the  teeth,  so  that  they  are  sharp  and  sufficiently  well 
defined  to  keep  the  gum  enamel  from  mixing  with  the  crown  enamel 
when  the  mould  is  pressed.  The  mould-trimmer  must  be  cautioned 
against  obliterating  this  line  of  deinarkation  between  crowns  and  gum. 

The  finishing  of  the  pin  side  of  the  mould  is  a  purely  mechanical 
operation,  and  is  done  with  square-edged  gravers  of  several  different 
sizes.  In  finishing  corners  and  levelling  straight  edges  a  small  variety 
of  square-edged  punches  can  be  used  to  advantage. 

When  the  mould  is  complete  in  respect  to  size  and  form  of  the  teeth, 
another  set  of  plaster  blocks  should  be  made  in  it,  for  the  purpose  of 
determining  whether  the  blocks  leave  the  mould  readily  when  slightly 
tapped  M'itli  a  wooden  mallet.  If  the  blocks  are  difficult  to  remove,  it 
will  be  evident  that  retaining  points  exist  which  retard  their  delivery  : 
these  are  easily  discovered  by  the  abrasion  they  make  upon  the  plaster, 
and  such  points  should  be  bevelled  sufficiently  to  allow  the  blocks  to  drop 
from  the  mould  without  injury  wlien  gently  tapped  by  the  mallet  on  its 
sides  or  ends.  Finally,  small  holes  are  to  be  drilled  in  the  pin  side  of 
moidd  for  the  platinum  pins  ;  these  holes  are  drilled  perpendicularly  to 
the  face  of  the  mould  and  parallel  witli  each  other,  five  for  each  front 
block,  four  for  the  bicuspid  blocks,  and  three  for  the  molar  blocks.  The 
mould  is  now  to  be  thoroughly  cleansed  of  all  particles  of  brass,  and  is 
ready  for  use. 

Moulding  and  Burning  Block  Teeth. — The  first  step  in  moulding 
is  to  oil  tlie  brass  mould  and  put  the  platinum  pins  in  tlie  small  holes 
drilled   for  their  reception  in  the  ])in  side  of  the  moulds.     The  point 


CARVING   BLOCK  TEETH.  253 

enamel  is  then  put  in  the  face  side  of  the  mould,  and  arranged  with  a 
small  spatula  to  the  full  thickness  at  the  point  and  tapered  down  sparingly 
toward  the  neck.  A  thin  coat  of  point  enamel  is  placed  on  the  lingual 
side  of  the  front  teeth  and  on  the  masticating  surfaces  of  the  bicuspids 
and  molars.  The  mould  is  then  laid  aside  to  dry  before  placing  the  gum 
enamel  in  place.  Some  makers  of  teeth  use  but  one  enamel :  instead 
of  applying  a  yellow  neck  enamel,  they  allow  the  body  to  show  at  the 
neck  of  the  tooth  ;  this  is  probably  done  to  save  time  and  labor,  but  it 
does  not  afford  the  best  results  as  to  translucency  and  natural  appearance. 

The  gum  enamel  is  mixed  with  water  and  made  just  stiff  enough  to 
stay  where  it  is  placed  by  the  enamel  spatula,  and  is  then  spread  evenly 
over  the  gum  surface  of  the  mould,  the  thickness  being  ascertained  by 
touching  the  point  of  the  spatula  to  the  mould  at  every  eighth  of  an 
inch.  The  placing  of  the  enamel  requires  more  experience  than  does 
any  other  part  of  the  moulding  process.  The  gum  enamel  must  be 
placed  close  to  the  necks  of  the  teeth,  but  must  not  be  allowed  to  im- 
pinge upon  the  crowns :  when  complete  it  is  allowed  to  dry  partially. 

The  body  is  applied  in  small  pieces  slightly  in  excess  of  the  quantity 
needed  for  each  block.  These  are  taken  up  with  a  small  spatula,  formed 
into  balls,  and  laid  on  the  pins  in  the  pin  side  of  the  mould.  The  two 
sides  of  the  mould  are  then  placed  quickly  together,  put  under  the 
press,  and  the  lever  applied  to  force  the  two  parts  of  the  mould  together. 
The  mould  is  then  taken  from  the  press,  put  in  an  iron  clamp,  and 
screwed  firmly  together  :  it  is  then  heated  on  a  stove  until  the  mould 
becomes  hissing  hot,  when  it  is  taken  off  and  allowed  to  cool  sufficiently 
to  handle.  The  clamp  is  then  removed,  the  mould  opened,  and  the  block 
made  to  drop  out  by  striking  the  mould  with  a  wooden  mallet. 

If  the  heating  has  been  carried  to  the  proper  point,  the  blocks  will  be 
found  hard  enough  through  the  agency  of  the  starch — which,  it  will  be 
remembered,  is  an  ingredient  in  the  formulas  for  bodies  for  moulded 
teeth — to  admit  of  trimming  :  this  is  done  with  small  files  and  separating 
saws.  After  trimming,  the  blocks  are  laid  aside  in  complete  sets  for 
burning. 

Moulds  for  Special  Cases. — Moulds  of  blocks  for  special  cases  can 
be  made  by  any  dentist  who  is  willing  to  give  his  time  and  labor  in  the 
production  of  highly  artistic  imitations  of  the  natural  organs  Fig.  293 
shows  models  made  by  the  author  for  such  a  special  case.  The  patient, 
a  lady  of  thirty-two,  had  lost  all  the  superior  teeth  in  consequence  of 
extensive  exostosis  of  the  roots.  The  incisors  and  cuspids  had  been 
preserved  by  the  patient,  and  served  as  valuable  guides  in  the  prepara- 
tion of  the  brass  mould.  The  bite  was  an  exceedingly  short  one,  as 
shown  by  Fig.  292,  yet  considerable  fulness  was  required  to  restore  the 
natural  expression  of  the  lip.  A  gold  plate  was  made  to  the  model,  the 
roots  of  the  natural  teeth  were  cut  off,  and  the  crowns  fitted  to  the  gold 
plate  just  as  ordinary  plain  teeth  would  be.  Calculating  the  total 
shrinkage  as  one-sixth  the  bulk  of  the  teeth,  allowance  was  made  by 
spaces  left  between  the  natural  teeth  (Fig.  293).  The  gums  were  formed 
of  wax  and  modelled  to  imitate  the  irregularities  of  nature  as  closely  as 
possible  ;  plaster  walls  were  then  made  in  the  manner  described  on  page 
243,  These  walls,  which  served  as  impressions  of  the  natural  teeth,  were 
removed  when  the  plaster  had  become   sufficiently  hard,  and  given  two 


254 


MOULDING  AND  CARVING  PORCELAIN  TEETH. 


coats  of  shellac  varnish  and  then  oiled.  The  plate  was  thoroughly- 
cleaned  of  adhering  wax,  the  walls  were  replaced,  and  plaster  was  run 
in  between  inside  and  outside  walls,  as  described  on  page  243.  By  this 
means  plaster  facsimiles  of  the  natural  teeth,  which  had  been  temporarily 
set  upon  the  plate,  were  obtained.  The  spaces  which  had  been  left  were 
then  filled  up  with  plaster  mixed  with  water  and  applied  with  a  camel's- 
hair  brush  until  the  width  and  length  of  each  tooth  were  increased  one- 
sixth,  and  the  outline  and  contour  of  the  natural  teeth  closely  imitated : 


Fig.  292. 


Fig.  293. 


this,  of  course,  required  careful  modelling  with  the  natural  teeth  for 
guides.  To  save  time,  two  blocks  of  four  teeth  each  were  made,  includ- 
ing the  central  and  lateral  incisors,  the  cuspids  and  the  first  bicuspids, 
the  second  bicuspids  and  molars,  ^vere  selected  from  ordinary  stock  teeth. 
Fig.  293  shows  the  arrangement  of  teeth  with  the  spaces ;  the  dotted 
line  indicates  the  additions  made  to  the  width  and  length  to  compensate 
for  shrinkage.  Fig.  294  shows  the  block  enlarged  and  modelled  to  imitate 


Fig.  294. 


Fro.  295. 


the  natural  teeth  and  gums.  A  plaster  mould  was  made  from  the  two 
plaster  blocks  of  four  teeth  each  ;  this  was  reproduced  in  hard  brass,  the 
trimming  and  adjusting  of  which  was  carefully  done,  so  that  no  change 
would  be  made  in  the  outline  or  contour  of  the  faces  of  the  teeth.  The 
mould  with  sample  of  shade  was  then  sent  to  a  manufacturer  to  have 
several  pairs  of  blocks  made.  Fig.  295  illustrates  the  block  after  burn- 
ing :  comparison  with  Fig.  294  will  show  the  difference  in  size  between 
the  unburned  and  burned  blocks. 


All-porcelain  Dentures. 

Under  this  heading  are  included  full  and  partial  dentures  made 
entirely  of  porcelain  in  one  continuous  piece.  The  most  favorable 
cases  for  this  form  of  denture  are  those  in  which  the  natural  gums  are 
very  much  absorbed,  resulting  in  a  very  flat  palatine  arch.  In  such 
cases  there  is  generally  room  for  sufficient  body  to  afford  reasonable 
strength.  The  following  is  the  method  given  by  Dr.  Wm.  E.  Hall  in 
carving  full  upper  sets  : 


ALL-PORCELAIN  DENTURES.  255 

Two  casts  are  taken  from  a  plaster  impression  of  the  edentulous 
upper  jaw.  A  thin  lead  plate  is  then  made  to  fit  one  of  the  casts  by 
burnishing  it  down  in  every  part.  A  piece  of  softened  beeswax  is  then 
put  on  the  ridge,  and  the  articulation  procured  in  the  usual  way  :  extra 
care  must  be  taken  to  trim  the  wax  to  the  exact  fulness  and  height 
required.  The  cast  and  wax  articulating  model  must  then  be  enlarged 
to  compensate  for  the  contraction  of  the  porcelain  in  burning :  this  con- 
traction amounts,  practically,  to  one-ninth  of  its  bulk. 

To  make  this  enlargement  the  cast  and  articulation  are  divided  with 
a  thin  saw  into  four  sections.  The  first  line  of  division  is  at  the 
centre  along  the  mesial  line  to  the  back  of  the  cast ;  the  second,  across 
the  cast  just  back  of  where  the  cuspid  teeth  are  located.  The  wax 
articulation  can  be  cut  freely  with  a  piece  of  fine  wire. 

Previous  to  this  division  the  bottom  of  the  cast  must  be  made  smooth 
and  level :  this  is  most  easily  done  by  pouring  mixed  plaster  on  a  piece 
of  window-glass  and  setting  the  cast  on  it,  letting  it  remain  until  the 
plaster  sets  hard,  then  trimming  the  edges. 

After  the  cast  has  been  divided  the  sections  are  again  placed  on  the 
piece  of  glass  in  such  a  manner  as  to  leave  between  each  of  them  a  space 
of  about  a  quarter  of  an  inch  :  if  in  irregular  cases  more  accuracy  is 
desired,  the  proportional  dividers  should  be  used.  The  space  must 
then  be  filled  with  freshly-mixed  plaster,  the  sections  being  held  in  posi- 
tion by  small  pieces  of  wax.  When  the  plaster  becomes  firm  a  new 
lead  plate  is  cut,  and  by  burnishing  is  made  to  fit  accurately.  The 
sections  of  the  wax  articulating  model  are  placed  on  the  enlarged  cast, 
and  the  interspaces  are  filled  with  melted  wax,  thus  making  the  model 
conform  to  the  size  of  the  enlarged  cast. 

An  outside  wall  must  then  be  made  for  moulding  the  body  :  this  is 
done  by  bending  a  piece  of  tin  round  the  front  and  sides  of  the  cast 
(with  the  wax  articulating  model  on  it)  to  get  the  correct  curve. 
The  tin  is  then  removed  one-fourth  of  an  inch  from  the  cast  in  front 
and  at  the  sides,  and  is  sustained  in  this  position  until  freshly-mixed 
plaster  is  poured  into  the  space  between  the  cast  and  tin.  When  this 
wall  is  trimmed  it  should  reach  one-fourth  of  an  inch  above  the  artic- 
ulating wax,  after  the  removal  of  which  the  wall  should  be  lined  with 
tin-foil.  Both  the  cast  and  the  wall  are  then  freed  from  all  small  pieces 
of  wax  or  plaster  and  perfectly  cleansed  for  moulding. 

The  body  is  prepared  as  directed  in  the  section  on  block-carving,  and 
is  moulded  on  the  lead  plate  made  to  fit  the  enlarged  cast :  the  lead 
plate  is  used  to  facilitate  the  removal  of  the  moulded  set  from  the  cast. 
The  lead  plate  and  inside  of  the  wall  should  be  oiled,  and  a  piece  of 
the  body  large  enough  for  the  purpose  laid  on  the  lead  plate  before  the 
wall  is  put  in  place,  and  gently  worked  over  the  edge  of  the  gum  with 
the  fore  finger  until  it  reaches  the  proper  limit  of  the  plate  line.  The 
Avail  is  then  put  in  place,  and  held  firmly  while  the  body  is  packed  up 
against  it  as  high  as  the  top  of  the  wall :  the  rest  of  the  body  is  then 
pressed  down  to  the  surface  of  the  lead  plate,  extending  back  as  far  as 
it  is  proposed  to  carry  the  plate.  The  body  is  then  allowed  to  dry  suf- 
ficiently to  carve  into  shape.  The  wall  is  removed  and  the  moulded  set 
examined  :  if  the  body  has  split  in  drying,  it  can  be  repaired  by  work- 
ing water  into  the  fissure  with  a  small  carving  knife.     The  moulded 


256  MOVLDINO  AND  CARVING  PORCELAIN  TEETH. 

piece  should  then  be  carved  out  roughly  on  the  cast  in  the  manner 
directed  in  the  section  on  block-carving.  When  roughly  carved  and 
reduced  to  nearly  the  proper  thickness,  the  piece  must  be  thoroughly 
dried  and  biscuit-baked  in  the  furnace  :  all  errors  in  the  carving  are  then 
corrected.  When  the  piece  has  been  enamelled  and  the  final  carving 
and  gumming  completed,  the  set  is  dried,  and  is  then  ready  for  the 
muffle. 

The  burning  of  such  large  pieces  of  porcelain  is  more  difficult  than 
the  burning  of  ordinary  blocks  :  it  is  not  admissible  to  draw  the  slide 
to  the  mouth  of  the  muffle  and  return  it  again  if  not  quite  fully  glazed, 
as  this  might  crack  the  set.  To  determine  the  proper  degree  of  glazing, 
small  pieces  of  body  with  enamel  on  them  are  placed  close  to  the  set  on 
the  side  near  the  mouth  of  the  muffle  :  these  may  be  pulled  out  with  a 
hooked  iron  rod  and  examined.  When  removed  from  the  furnace  to  the 
cooling  muffle,  the  set  should  not  be  allowed  to  remain  in  the  open  air 
a  moment  longer  than  is  necessary  to  carry  it  thither.  The  muffle  must 
be  immediately  closed  with  a  hot  stopper  from  the  furnace.  The  extra 
precaution  is  sometimes  taken  of  covering  the  muffle  with  hot  ashes 
to  retard  the  cooling  process. 

The  requisite  care  in  adjusting  the  set  on  the  slide  for  burning  must 
not  be  omitted  :  the  sagging  of  the  palatine  arch  is  of  frequent  occur- 
rence if  it  is  not  properly  supported.  If  the  whole  weight  of  the  piece 
should  rest  on  two  or  three  points  of  the  gum,  it  might  result  in  serious 
warping.  To  provide  against  sucli  a  result,  clay  supports  are  moulded, 
upon  which  the  piece  of  carved  work  rests  and  is  sustained  during  the 
burning  process.     The  formula  for  the  composition  of  the  support  is — 

Kaolin  or  white  clay,  1  part ; 

Pulverized  quartz,  2  parts. 

Mix  with  sufflcient  water  to  form  a  mass  plastic  enough  to  mould  in 
small  pieces  to  the  under  side  of  the  carved  set. 

Four  small  pieces  made  into  balls  are  required — three  in  the  groove 
directly  under  the  teeth,  the  fourth  under  the  palatine  portion  of  the 
set.  These  balls  are  placed  on  a  piece  of  glass  in  position  for  the 
teeth  to  be  pressed  firmly  down  on  them,  and  are  left  undisturbed 
until  the  supports  are  dry  enough  to  be  safely  removed.  They  are 
then  to  be  surfaced  with  powdered  quartz,  and  dried  to  be  ready 
for  use. 

When  the  teeth  are  removed  from  the  cooling  muffle  the  set  will 
require  more  or  less  grinding  to  fit  the  original  cast,  which,  as  will  be 
remembered,  was  left  unenlarged.  This  is  accomplished  with  corundum 
wheels  and  points.  To  facilitate  the  grinding  the  prominent  parts  of 
the  cast  are  coated  with  a  mixture  of  rouge  and  oil,  which  will  spot  the 
under  side  of  the  set  and  show  the  exact  place  to  be  ground  oif  to  make 
the  case  fit  solidly  on  the  cast. 

Very  small  corundum  wheels  and  points  are  needed  for  grinding  the 
more  inaccessible  places  and  for  making  small  depressions  for  the  rugse, 
etc.  :  these  wheels  and  points  should  be  mounted  on  long  thin  mandrels, 
and  be  held  either  in  the  hand-piece  of  a  dental  engine  or  in  a  chuck 
attached  to  the  grinding  lathe. 


ALL-PORCELAIN  DENTURES.  257 

With  these  appliances  the  successful  result  will  depend  upon  the  skill 
and  judgment  of  the  operator. 

Burning-, — In  manufacturing  on  a  large  scale  the  blocks  are  arranged 
in  complete  sets  on  a  fire-clay  slide  covered  with  coarse  quartz.  These 
slides  are  6|  inches  in  width  by  9|^  inches  in  length :  they  have 
raised  edges  to  retain  the  quartz  which  serves  as  a  bed  for  the 
blocks ;  they  hold  from  twelve  to  fifteen  sets  according  to  the  size 
of  the  blocks. 

The  furnaces  used  by  the  large  manufacturers,  having  a  capacity  of 
three  or  four  hundred  sets  per  day  for  one  furnace,  are  built  of  ordinary 
red  brick  held  together  with  iron  bars,  the  inside  being  made  of  fire- 
brick. These  furnaces  are  square,  with  a  heating  oven  directly  over  the 
fire,  the  muffle  being  placed  lower  down  :  the  furnace  is  connected  with 
the  smokestack  by  flues  at  the  top.  The  muffles  are  constructed  of  the 
best  prepared  fire-clay,  27  inches  long,  8  inches  wide,  5f  inches  high, 
and  1^  inches  thick.  The  muffle  must  be  thoroughly  swabbed  with  clay 
mixed  thin  with  water,  to  fill  up  all  cracks  or  defects  through  which  the 
gases  from  the  fuel  might  enter  the  muffle.  Such  accidents  are  of  fre- 
quent occurrence  in  burning,  and  are  always  ruinous  to  the  teeth,  the  gas 
generally  imparting  to  them  a  ghastly  blue  appearance. 

As  it  is  necessary  to  cool  the  blocks  very  gradually  after  burning  to 
prevent  cracking,  they  are  placed  in  cooling  muffles  or  ovens  made  of 
flat  pieces  of  fire-brick  about  12  inches  square.  These  are  built  in 
tiers  of  ten  in  each  row  :  each  oven  is  provided  with  a  loose  fire-brick 
stopper. 

Large  furnaces  of  this  description  require  a  charge  of  nearly  half  a 
ton  each  of  the  best  grade  of  anthracite  coal.  The  slide  containing  the 
teeth  is  placed  in  the  heating  muffle  at  the  top  of  the  furnace  before 
burning  :  this  preliminary  heating  prepares  them  for  the  higher  temper- 
ature of  the  muffle,  into  which  they  are  lifted  on  a  flat  iron  shovel ;  the 
door  is  then  closed.  The  length  of  time  required  for  burning  the  blocks 
on  each  slide  varies  according  to  the  heat  of  the  muffle :  about  fifteen 
minutes  is  allowed  each  slide,  and  the  draft  is  regulated  by  dampers 
arranged  on  the  top  of  the  smokestack,  operated  from  the  inside  of  the 
furnace-room.  When  the  teeth  glaze  in  less  than  fifteen  minutes,  the 
damper  should  be  closed  enough  to  diminish  the  draft.  A  too  rapid  heat 
tends  to  burn  out  or  vaporize  the  colors  of  the  enamels.  The  proper 
glazing  of  the  teeth  is  ascertained  by  placing  them  under  a  gas-jet,  and 
when  the  final  burning  is  satisfactorily  accomplished  they  are  put  in  the 
cooling  muffle,  protected  from  the  air  by  a  door  or  stopper,  and  left  un- 
disturbed until  quite  cold. 

Furnaces,  Muffles,  Slides. — These  are  made  of  burnt  clay  pounded 
into  a  coarse  powder  and  mixed  with  fresh  clay  in  proper  proportions  to 
form  a  plastic  mass  for  moulding.  This  combination  of  burnt  and  un- 
burned  clay  is  made  to  lessen  the  shrinkage  which  occurs  in  all  clays 
when  exposed  to  high  temperatures.  After  being  kiln-burned  the  muffles 
will  always  be  found  to  be  somewhat  porous,  and,  unless  the  pores  are 
filled  up  with  kaolin  mixed  with  water  and  well  rubbed  in  with  a  sponge 
inside  and  outside,  gases  from  the  fuel  will  get  through  and  discolor  the 
teeth.  The  muffle  of  the  furnace  should  receive  a  thorough  swabbing 
with  fire-clay  or  kaolin  after  every  heating. 
17 


258 


MOULDING   AND   CARVING   PORCELAIN  TEETH. 


The  furnace  generally  used  in  burning  carved  block  work  is  shown 
in  Fig.  296.  It  is  oval  in  shape :  the  muffle,  occupying  the  shortest 
diameter,  leaves  sufficient  room  inside  for  the  fuel.  The  height  from 
the  top,  exclusive  of  the  pipe  extension 
to  the  bottom,  is  32  inches.  The  fur- 
nace is  in  three  sections,  the  muffle 
being  fixed  in  the  middle  piece,  which 
is  15  inches  high;  the  dome,  or  top 
piece,  is  8  inches  high  ;  the  ash-pit,  or 
lower  piece,  holding  the  iron  bars  which 
serve  as  a  grate,  is  9  inches  high.  The 
width  or  largest  diameter  of  the  mid- 
dle pieces  is  18  inches.  The  other 
sections  correspond  in  width  with  the 
middle  piece.  The  muffle  is  3|  inches, 
inside  measurement.  This  part  of  the 
furnace  requires  constant  care  and  at- 
tention, as  frequent  exposure  to  very 
high  temperatures  causes  sagging  and 
partial  collapse  of  the  sides,  by  which 
its  width  may  be  diminished  :  for  this 
reason  the  slide  should  not  measure 
more  than  2|  inches  in  width.  This 
is  sufficient  to  hold  eight  carved  blocks 
without  danger  of  contact  with  each 
other.  The  door  of  the  muffle  is  at- 
tached to  the  sheet-iron  jacket  of  the 

furnace  by  a  hinge,  and  when  closed  is  securely  held  by  a  thumb-latch. 
All  the  parts  of  the  furnace  are  bound  or  covered  with  sheet  iron,  as 
seen  in  the  illustration. 

One  charge  of  coke  will  burn  but  one  slide  of  carved  blocks.  If  the 
coke  is  well  packed,  the  burning  heat  will  last  for  half  an  hour.  The 
combustion  of  coke  is  very  rapid,  and  no  time  is  to  be  lost  in  taking 
advantage  of  the  proper  degree  of  heat  for  burning  while  it  lasts.  The 
fire  is  made  with  small  pieces  of  kindling-wood  laid  upon  the  iron  bars 
under  the  muffle  :  these  are  lighted,  and  sufficient  coke,  not  of  too  large 
size,  is  shovelled  in  until  even  with  the  top  of  muffle  :  the  stopper  is 
then  placed  in  the  dome  section  of  the  furnace,  and  when  the  coke  is 
ignited  and  the  lower  part  of  the  muffle  is  slightly  red  hot,  the  draft  is 
removed.  All  the  ashes  of  the  kindling-wood  are  carefully  raked  out ; 
fresh  coke  is  added  and  carefully  packed  under  the  muffle  and  quite  up 
to  the  stopper,  until  there  is  no  room  for  more  fuel ;  the  stopper  is  then 
placed  in  and  luted  up  with  clay.  Anthracite  coal  is  used  in  the  same 
way  :  the  burning  temperature  can  be  maintained  by  it  for  a  much 
greater  length  of  time,  but  the  long-continued  heat  which  it  affords  is 
objectionable,  and  is  more  or  less  destructive  to  the  muffle.  Two  or 
three  slides  can  be  burned  at  one  heating  with  hard  coal. 

When  ready  for  burning  the  blocks  are  placed  on  a  bed  of  coarse 
quartz  of  the  size  of  scouring  sand.  The  blocks  are  stood  nearly  upright 
on  the  gum  edges,  and  the  coarse  quartz  is  banked  up  under  them  in  a 
manner  to  thoroughly  support  them,  so  that  they  will  not  warp  or  twist 


IMPROVEMENTS  IN  FURNACES. 


259 


while  partially  fused.  The  quartz  must  not  be  allowed  to  touch  the 
outside  or  enamelled  part  of  the  block.  The  blocks  must  be  thoroughly 
dried  before  they  go  into  the  hot  muffle.  The  slide  is  then  gradually 
placed  in  the  mnflfle  by  means  of  a  pair  of  tongs,  and,  a  narrow  muffle- 
shovel  held  by  the  left  hand  under  it  to  guard  against  breaking,  it  is 
lifted  carefully  to  the  middle  of  the  slide  without  jarring.  The  door  is 
left  open  until  all  vegetable  matter  is  burned  off,  when  it  is  closed,  and 
not  again  opened  for  about  ten  minutes.  If  the  temperature  has  reached 
the  burning-point,  the  blocks  Avill  appear  slightly  glazed  and  the  enamel 
somewhat  colored  :  the  door  should  then  be  closed  for  three  or  four 
minutes,  the  slide  drawn  to  the  mouth  of  the  muffle  and  quickly  exam- 
ined to  ascertain  whether  the  blocks  are  thoroughly  glazed  :  if  not,  they 
are  to  be  returned,  the  door  closed,  and  examined  again  in  two  or  three 
minutes,  when,  if  properly  glazed,  they  are  to  be  immediately  placed  in 
the  cooling  muffle  and  left  until  quite  cold. 

The  cooling  muffle  is  intended  to  protect  the  blocks  while  hot  from 
contact  with  the  cool  air :  an  ordinary  muffle  is  used  for  this  purpose, 
and  is  closed  with  the   red-hot  stopper  of  the  fuel-hole  in  the  dome. 

Improvements  in  Furnaces. 

The  first  important  modification  on  the  old-fashioned  furnace  shown 
in  Fig.  296  was  made  by  Dr.  Ambler  Tees  in  1880.  His  improvement 
consists  in  the  great  reduction  of  size  of  the  apparatus,  and  in  the  quick- 
ness with  which  it  can  be  made  to  do  its  work.  It  was  intended  prin- 
cipally for  use  in  the  continuous-gum  process,  but  may  be  employed  in 
burning  blocks,  single   teeth,  porcelain   crowns  and   inlays,  etc.      The 

Fig.  298. 


The  Verrier  gas  furnace. 


The  bi-muffle  gas  furnace  of  Dr.  C.  H.  Land. 


dimensions  of  the  furnace  are— ISJ  inches  high,  12  inches  wide,  and  8 
inches  deep,  with  walls  1  inch  thick,  being  divided  into  three  sections, 
which  so  reduces  its  weight  that  very  little  eifort  is  required  in  handling 


260  MOULDING  AND   CARVING  PORCELAIN  TEETH. 

it.  Scarcely  more  than  half  a  peck  of  coke  is  necessary  for  each  burn- 
ing, and  when  the  draft  is  good  the  body  of  a  continuous-gum  denture 
can  be  fused  in  about  thirty-five  minutes  after  the  fire  is  lighted  :  at 
other  times,  when  the  draft  is  not  particularly  strong,  the  burning  can 
be  accomplished  in  about  fifty  minutes.  An  illustration  of  this  furnace, 
with  directions  for  its  charging  and  management,  will  be  found  on  page 
457  (chapter  on  the  Continuous-gum  Process). 

Within  the  past  few  years  much  attention  has  been  given  to  the  con- 
struction of  furnaces  which  can  be  operated  successfully  without  the  use 
of  solid  fuels :  this  has  been  accomplished  in  the  use  of  gas  in  combina- 
tion with  the  air-blast.  Dr.  C.  H.  Land  of  Detroit,  Michigan,  has 
invented  four  diiferent  forms  and  several  styles  of  gas  furnaces  for  the 
fusing  of  porcelains  and  melting  of  metals,  which  are  said  to  be  much 
more  economical,  cleaner,  and  have  made  the  fusing  of  porcelain  safer 
and  more  certain  in  results  than  is  possible  with  coal  or  coke. 

The  successful  application  of  these  later  devices  gave  promise  of 
greater  economy  of  time  in  firing,  freedom  from  dirt,  smoke,  and  pro- 
longed heat  after  the  work  was  done — the  greatest  objections  to  the  old- 
fashioned  solid-fuel  furnaces.  The  liability  to  the  vexatious  accident  of 
"  gasing,"  however,  still  remained ;  but  in  later  improvements  this 
objection  has,  it  is  believed,  been  entirely  overcome.  In  the  bi-muffle 
gas  furnace  of  Dr.  Land  it  is  claimed  that  high-grade  porcelain  can  be 
fused  in  from  six  to  fifteen  minutes  :  it  has  been  found  very  useful  in 
changing  the  forms  or  color  of  plain  teeth,  in  porcelain  crown-  and 
bridge-work,  in  adding  any  style  of  platinum  pins  or  loops  to  suit 
special  cases,  making  sections  of  block  work,  changing  plain  teeth  into 
gum  teeth,  and  making  porcelain  inlays,  etc. 

The  Verrier  gas  furnace  is  an  invention  of  Dr.  A.  B.  Verrier  of  Wey- 
mouth, England  (Fig.  297).  It  is  operated  by  coal  gas  or  benzoline 
vapor  in  conjunction  with  the  blast  from  the  foot-bellows.  Its  dimen- 
sions are  6  cubic  inches,  and  it  is  so  small  that  it  may  be  placed  upon  a 
bracket  in  the  workroom.  The  inventor  claims  that  within  ten  minutes 
from  the  time  of  starting  the  fire  sufficient  heat  will  be  obtained  to  fuse 
the  body  and  gum  enamel. 

The  Do-wnie  Furnace. — This  furnace  is  designed  for  baking  crowns, 
porcelain  inlays,  sections,  etc.,  and  is  undoubtedly  an  improvement  on 
any  gas  furnace  which  has  preceded  it.  The  muffle  is  made  of  platinum, 
thus  entirely  obviating  the  danger  of  "gasing"  which  is  so  liable  to 
happen  in  the  porous  fire-clay  muffle.  It  does  its  work  so  quickly  that 
porcelain  inlays  can  be  fused  in  about  one  minute  and  crowns  in  from 
two  to  three  minutes  from  the  time  the  furnace  is  lighted.  The  size 
of  the  muffle  is  ^  of  an  inch  wide  by  f  of  an  inch  high.  The  openings 
at  the  sides  of  the  entrance  to  the  muffle  are  temporary  ovens  in  which 
to  set  the  work  to  gradually  cool  after  baking.  The  operator  can  easily 
see  the  work  while  baking,  and  readily  distinguish  when  the  fusing  of 
the  porcelain  is  complete.  With  it  broken  teeth  may  be  repaired,  and 
crowns   and  porcelain   teeth  may  be  built  to  any  shape  desired. 

A  small  platinum  tray  takes  the  place  of  a  slide  :  the  crown  inlay  or 
tooth   is  placed  upon  it  and  carried  into  the  muffle  (Fig.  299). 

To  Make  the  Downie  Croicn. — Take  a  strip  of  platinum  of  sufficient 
width  for  the  band.    Cut  the  band  a  thirty-second  of  an  inch  longer  than 


IMPROVEMENTS  IN  FURNACES. 


261 


Fig.  299. 


the  circumference  of  the  root ;  level  both  ends  before  lapping  them  and 
solder  with  pure  gold.  Fit  the  band  to  the  root,  letting  it  extend  slightly 
under  the  free  margin  of  the  gum 
and  down  beyond  the  surface  of 
the  root  about  as  much  as  it  ex- 
tends above.  Remove  the  band 
and  clip  out  V-shaped  cuts  all 
around.  When  the  band  is  re- 
placed in  position  the  points  are 
to  be  bent  down  upon  and  over 
the  root.  The  band  ^vill  then 
appear  as  in  Fig.  300,  a.  Select 
a  plate  tooth,  take  a  square 
iridio-platinum  wire  of  sufficient 
size  for  the  post,  taper  one  end, 
and  tiatten  the  other  with  a 
hammer  a  little  wider  than  the 
space  between  the  pins  of  the 
tooth  ;  file  a  notch  in  each  side, 
and,  ])laci ng  it  between  the  plat- 
inum pins,  bend  them  over  as 
in  Fig.  300,  6,  and  solder  with 
pure  gold.  If  the  bite  is  close, 
grind  the  pins  down  to  give 
room.  After  fitting  the  tooth 
to  position  by  bending  the  post, 
if  necessary,  or  grinding  the 
base  of  the  tooth,  put  a  napkin 
in  the  mouth,  dry  the  root  and 
adjacent  parts,  and,  Avarming 
a  small  pellet  of  sticky  wax, 
place  it  on  the  end  of  the  root 
and  force  the  post  through  it 
and  the  tooth  to  its  proper  relation  to  the  root.  Press  the  wax  up 
against  the  back  of  the  tooth  and  ascertain  whether  the  articulation 
is  correct.  Fig.  300,  c,  shows  the  tooth  set  on  the  root  with  wax 
backing.  Carefully  remove  it  by  loosening  the  band  with  a  hoe-shaped 
excavator.       Remove    the    wax    from    around    the    post   where    it    has 

Fig.  300. 


Downie's  porcelain  crown  furnace. 


been  forced  into  the  canal.  Mix  silex  and  plaster  in  the  proportion  of 
2  parts  of  plaster  to  3  parts  of  silex,  and  fill  the  band  with  the  invest- 
ment, building  u})  slightly  around  the  post :  after  the  investment  sets 
boil  out  the  wax. 


262  MOULDING  AND   CARVING  PORCELAIN  TEETH. 

Fig.  300,  d,  shows  the  tooth  with  the  investment  in  the  band  and  the 
wax  removed.  The  porcelain  body  is  now  built  on  until  the  tooth  cor- 
responds in  shape  to  the  natural  teeth,  when  it  is  put  in  the  furnace 
and  fused.  More  body  is  then  added  and  the  band  covered  so  as  to  con- 
ceal it :  the  crown  is  then  fused  a  second  time,  when  it  may  be  considered 
as  finished,  as  seen  in  Fig.  300,  e. 

In  baking  the  crown  is  placed  on  the  platinum  tray,  as  shown  in  Fig. 
300,  /,  putting  the  post  through  the  hole  in  the  back  end  of  the  tray,  face 
up.     This  prevents  the  tooth  being  fused  fast  to  the  tray. 

Ordinary  teeth  for  vulcanite  work  answer  well  in  making  this  crown. 
When  they  are  used  the  post  should  be  soldered  between  the  pins  with 
pure  gold. 

In  the  case  of  bicuspids  and  molars,  especially  where  the  bite  is  short, 
it  is  often  better  to  build  them  up  entirely  with  the  body  and  not  use  any 
tooth  or  facing.  The  author  has  frequently  secured  satisfactory  results 
in  the  case  of  bicuspids  and  molars  by  making  a  cap  of  platinum  and 
then  enamelling  it  with  a  body  which  corresponds  in  color  with  the 
natural  teeth. 

The  Downie  Furnace  for  Bridge-work. — This  is  of  larger  size  and 
greater  capacity  than  the  preceding,  and  is  designed  especially  for  bridge- 
work,  gum  sections,  etc.  It  has  a  platinum  muffle  1-|  inches  wide  and 
1  inch  high.  Crowns  and  bridges  can  be  fused  in  this  furnace  in  from 
two  to  four  minutes  from  the  time  the  furnace  is  lighted,  although,  for 
the  greater  safety  of  the  teeth,  it  is  better  to  light  the  gas  and  allow  it  to 
burn  for  a  few  minutes  without  the  blast.  The  opening  of  the  muffle  is 
not  closed  while  the  crown  or  bridge  is  being  enamelled,  and  tlie  work 
may  be  watched  constantly  until  the  proper  point  of  glazing  is  reached. 
The  temperature  falls  the  instant  the  gas  is  extinguished  :  the  crown  or 
bridge  may  therefore  be  left  in  the  muffle  until  it  is  entirely  cold. 

Porcelain  bridge-work  has  many  advantages,  amongst  which  may  be 
mentioned  cleanliness  and  the  complete  concealment  of  the  metal  frame- 
work. Wherever  a  cap  or  ferule  is  visible,  it  is  only  necessary  to  extend 
the  porcelain  coating  to  it  and  it  appears  as  a  continuation  of  the  tooth. 
The  Downie  Furnace  for  Continuous-guni  "Work. — This  is  a 
similar  furnace,  made  large  enough  to  receive  a  full  upper  or  lower  den- 
ture. Like  the  two  preceding  ones,  the  muffle  is  formed  of  platinum, 
and  all  liability  to  cracking  of  the  muffle  and  the  consequent  gasing  of 
the  work,  so  frequent  where  fire-clay  muffles  are  used,  is  entirely  done 
away  with.  After  a  short  preliminary  heating  without  the  blast  to  pre- 
vent fracture  of  any  of  the  teeth,  the  case  may  fused  in  about  twenty 
minutes  from  the  time  the  furnace  is  lighted,  the  front  of  the  muffle 
being  open,  so  that  the  proper  degree  of  fusion  is  easily  seen  the  instant 
it  is  reached. 

Tempering  ovens  are  arranged  on  each  side  of  the  opening  into  the 
muffle,  and  the  hearth  is  provided  with  two  slides,  so  that  the  case  can 
be  brought  out  on  to  the  hearth  and  put  into  the  tempering  oven  by 
simply  shoving  the  slide  to  one  side  by  the  small  porcelain  knob  seen  at 
the  bottom  of  the  hearth. 

The  fuel  used  with  the  Downie  furnace  is  either  ordinary  illuminating 
gas  or  gas  generated  from  gasoline,  the  latter  being  quite  as  effec- 
tive as  coal  gas,  and  much  cheaper.     An  apparatus  has  been  designed 


IMPROVEMENTS  IN  FURNACES. 


263 


for  use  with  the  Downie  furnace,  which  it  is  claimed  generates  gas  at  a 
cost  of  about  ten  cents  per  one  thousand  feet.  This  gives  dentists  prac- 
tising in  small  towns  the  same  advantage  as  those  in  cities,  as  it  will 
operate  either  of  the  fnrnaces  above  described  equally  as  well  as  coal  gas. 
Fig.  301  illustrates  the  foot-bellows  used  for  supplying  the  air-blast : 
it  is  made  in  three  sizes  to  correspond  with  the  capacity  of  each  furnace. 
These  bellows  liave  improved  rubber  treadle  feet  to  keep  them  from 
shifting  when  in  use,  and  nets  made  of  strong  flax  cord.  Their 
dimeusions  are  as  follows  : 

Small,       8^  by  9^  inches. 

Medium,  10  by  11  L     « 

Large,      12  by  13       " 

Fig.  301. 


Foot-bellows  for  the  Downie  furnaces. 


Fro.  302. 


Dr.  John  H.  Mayer  describes  a  preparatory  muffle  and  annealing 
ovens  to  be  used  with  an  oil  furnace  for  continuous-gum  and  other 
porcelain  work.  The  preparatory  muffle 
(Fig.  302)  is  placed  in  the  elbow  of  the 
furnace-pipe,  and  so  arranged  as  to 
utilize  the  escaping  heat  as  it  passes 
upward  from  the  furnace.  The  heat 
distributed  around  the  muffle  reaches 
a  temperature  of  about  1800°  F.  This 
preparatory  muffle  is  large  enough  to 
receive  five  cases,  which  can  be  placed 
in  it  before  the  oil  is  ignited,  and  grad- 
ually heated  up,  and  when  the  lower 
muffle  has  attained  the  necessary 
baking  heat  the  cases  may  one  by  one 
be  transferred  to  it,  and  when  satis- 
factorily fused  placed  in  the  asbestos- 
lined  ovens  (Fig.  302). 

The  improvement  claimed  for  this 
furnace  is  that  in  ordinary  single-muffle 
furnaces   but   one   case   at  a  time   can 

receive  attention,  while  by  the  prepara-  ^'^^"''^  °^'  '^™'''' 

tory-muffle  arrangement  five  cases  may  be  fused  in  rapid  succession. 


264  MOULDING   AND   CARVING   PORCELAIN  TEETH. 


Electric  Heat  in  Prosthetic  Dentistry. 

Dr.  Levitt  E.  Custer  has  constructed  a  small  electric  oven  for  fusing 
porcelain,  the  heating  principle  of  which  is  a  coil  of  iridio-platinum  wire 
imbedded  in  a  refractory  mixture  just  deep  enough  to  be  supported  while 
highly  heated,  and  yet  to  radiate  its  heat  directly  into  the  oven-cavity. 
This  latter  furnace  consists  of  an  upper  and  lower  section  somewhat  the 
shape  of  the  flasks  used  in  rubber  work,  with  an  inner  cavity  large 
enough  to  contain  an  upper  or  lower  denture  of  the  maximum  size,  and 
with  such  arrangement  of  the  wire  that  all  parts  receive  the  same  degree 
of  heat.  (See  chapter  on  Continuous-gum  Work.)  The  upper  half  is 
hinged  to  the  lower.  The  electric  connection  is  automatically  made  by 
closing  the  sections  of  the  furnace.  There  are  two  openings  through 
which  the  fusing  process  may  be  watched.  These  are  placed  at  such 
positions  that  rays  of  light  entering  one  will  be  reflected  out  by  the  plate 
through  the  other.  This  overcomes  the  intense  glare  of  the  heat,  and  at 
the  same  time  brings  the  plate  clearly  into  \'\e\\,  making  it  possible  for 
the  operator  to  accurately  determine  the  degree  of  fusion. 

There  are  many  possible  advantages  offered  by  the  use  of  electricity 
in  fusing  porcelain.  It  gives  rise  to  no  products  of  combustion,  and  it  is 
therefore  impossible  to  produce  with  it  the  condition  knoAvn  as  "gasing,'' 
and  it  has  been  observed  that  porcelain  fused  by  it  not  only  possesses 
unusual  clearness,  but  appears  to  be  more  dense.  The  accuracy  with 
which  electric  heat  can  be  regulated  by  means  of  the  rheostat,  the  clean- 
liness, simplicity,  and  freedom  from  noise  and  odor,  are  advantages  over 
the  older  methods  of  burning  porcelain  work. 

Electricity  is  so  easily  controlled  that  it  is  not  improbable  that  an 
automatic  appliance  will  soon  be  invented  to  regulate  the  heat  according 
to  the  fusibility  of  the  porcelain  treated. 

The  best  current  with  which  to  operate  tlie  Custer  furnace  is  the 
Edison,  but  the  52-volt  alternating  current,  while  somewhat  slower, 
serves  the  purpose  very  well. 

The  procedure  in  the  practical  use  of  the  oven  is  exceedingly  simple. 
The  case  is  placed  on  the  tray  in  the  loAver  section,  and  the  upper  is  then 
closed  down.  The  lever  of  the  rheostat  is  placed  on  the  first  button,  and 
heat  for  drying  out  the  case  is  quickly  obtained.  When  the  operator  is 
satisfied  that  there  is  no  more  moisture  present  he  raises  the  heat  by 
pushing  the  lever  to  the  right.  (See  chapter  on  Continuous-gum  Work.) 
If  he  allows  two  minutes  to  each  button,  it  will  require  from  twenty  to 
twenty-five  minutes  to  reach  the  fusing-point.  If  it  is  a  crown  or 
bridge,  less  time  may  be  consumed  in  raising  the  heat  without  danger  to 
the  case,  and  it  may  be  fused  in  from  ten  to  fifteen  minutes  by  throwing 
the  lever  over  more  rapidly.  When  the  desired  temperature  has  been 
obtained  and  the  fusing  of  the  porcelain  is  complete,  the  lever  of  the 
rheostat  is  throAvn  l)ack  and  the  current  cut  off*.  At  that  instant  the 
heat  begins  to  go  down,  so  that  neither  oA'er-fusing  nor  loss  of  brilliancy 
in  the  gum  color  can  occur. 

To  Fuse  Platinum. — Disconnect  the  rheOvStat  and  attach  an  arc-light 
carbon  to  one  wire  and  a  carbon-battery  plate  to  the  other.  Place  the 
platinum  upon  the  carbon  plate  and  touch  the  platinum  with  the  pencil. 
Upon  raising  the  pencil  an  arc  will  be  formed  upon  the  platinum,  Avhich 


PIN  LESS  GUM  AND  PLAIN  TEETH. 


265 


will  then  be  melted.     If  there  is  any  noise  in  the  arc,  reverse  the  connec- 
tions of  the  wires  to  the  plate  and  pencil. 

There  can  be  scarcely  a  doubt  that  electricity  will  be  made  to  meet 
all  the  requirements  of  the  prosthetic  dentist  in  the  fusing  of  porcelain 
as  w^ell  as  in  the  melting  of  metals,  and  the  electric  oven  of  Dr.  Custer 
may  even  now  be  truly  said  to  be  in  advance  of  any  of  the  older  means 
of  obtaining  high  temperatures. 

English  Tube  Teeth, 

These  are  of  the  class  of  single  plain  teeth.  They  are  made  with  a 
platinum  tube  burned  in  the  porcelain,  extending  entirely  through  the 
centre  of  the  tooth,  corresponding  to  its  long  axis.  In  form  these  teeth 
are  excellent  imitations  of  the  natural  organs.  The  texture  of  the 
material  of  which  they  are  made  resembles  very  closely  that  of  the 
natural  teeth.  The  sliape  of  an  English  tooth  may  be  altered  by  grind- 
ing with  the  corundum  wheel,  and  the  ground  surface  may  be  completely 
restored  to  the  original  condition  by  polishing.  On  account  of  the  close- 
ness of  texture  and  greater  strength  of  the  porcelain  of  which  English 
teeth  are  made  many  expert  bridge-workers  prefer  them  to  those  of 
American  make.  (For  full  details  in  the  setting  of  tube  teeth,  with 
their  a]>plication  to  crowns  and  bridges,  the  reader  is  referred  to  the 
chapter  on  English  Tube  Teeth.) 

PiNLESs  Gum  and  Plain  Teeth. 

Owing  to  the  increased  demand  and  consequent  advance  in  the  price 
of  jilatinum  incident  to  its  uses  in  electric  lighting,  manufacturers  have 
endeavored  to  dispense  with  })ins  in  all  classes  of  teeth  designed  for 
rubber  work.  The  illustrations  rejirescnt  a  new  form  of  pinless  teeth. 
In  these  the  holes  are  so  constructed  that  the  rubber  vulcanizes  well  in 
the  teeth  and  unites  them  firmly  to  the  plate,  and  it  is  claimed  that  they 
hold  equally  as  well  as,  if  not  better  than,  ^\n  teeth. 

Fig.  303. 


Single    Plain    Teeth    with    Countersunk    Pin. — The    countersunk 
tooth  crowns  were  introduced  by  the  S.  S.  White  Dental  Manufacturing 


266 


MOULDING  AND   CARVING   PORCELAIN  TEETH. 


Co.  in  1885.  It  has  beeu  said  of  them  that,  properly  mounted,  they 
ibrm  dentures  which  fairly  rival  continuous-gum  work  in  naturalness  of 
appearan(;e,  witiiout  the  oljjectionablc  weiglit  of  the  latter.  Their  close 
conformity  in  contour  to  the  natural  organs  makes  them  much  more 
acceptable  to  the  tongue  than  teetli  backed  in  the  ordinary  manner, 
renders  articulation  easier  and  more  distinct,  and  prevents  disclcjsure  of 
artificiality  when  the  mouth  is  opened.  In  addition,  it  is  claimed  that 
these  crowns  allow  of  greater  facility  of  adaptation  to  the  maxillary 
ridge,  and  that  the  tlenture  is  in  no  degree  inferior  in  strength  to  any 
that  have  yet  been  made  on  a  plastic  base. 


These  crowns  may  be  used  with  either  vulcanite,  celluloid,  or  fusible- 
metal  base. 

For  a  vulcanite  base  the  case  should  be  flashed  in  the  usual  way,  but 
in  packing  each  countersink  should  be  carefully  filled  with  small  pieces 
of  rubber  to  ensure  the  rubber  being  thoroughly  forced  into  the  counter- 
sink and  around  the  pins. 

AVhen  the  base  is  to  be  of  celluloid,  the  countersinks  must  be  first 
filled  with  small  pieces  of  celluloid  moistened  with  spirits  of  camphor, 
and  the  case  Avell  heated  before  bringing  the  two  parts  of  the  flask 
together. 

For  a  fusible-metal  base  every  precaution  should  be  taken  to  expel 
the  air  from  the  countersinks,  such  as  jarring  the  flask  or  tapping  it  with 
a  mallet.  It  would  probably  l)e  safer  to  use  in  pouring  a  conduit  which 
Avould  give  the  pressure  of  a  column  of  the  melted  alloy  :  this  would 
afford  a  sharper  casting  and  be  nearly  certain  to  fill  all  the  countersinks 
as  well  as  all  other  deep  places  in  the  matrix. 

Great  improvement  has  been  made  in  the  variety  of  sizes  and  forms 
of  porcelain  teeth  designed  for  use  in  the  continuous-gum  process. 
Generally,  these  teeth  are  supplied  with  but  one  long  platinum  pin,  by 
which  the  teeth  are  soldered  to  the  backing  strip.  While  the  single  pin 
is  probably  sufficient  for  strength,  it  is  often  found  to  be  inadequate  as 
a  means  of  holding  the  teeth  securely  in  position  while  the  denture  is 


PINLESS  GUM  AND  PLAIN  TEETH. 


267 


being  burned.  To  prevent  lateral  movement  of  the  teeth,  and  to  main- 
tain their  correct  relation  to  each  other,  Dr.  C.  H.  Land  has  recom- 
mended the  arrangement  of  two  lateral  pins  to  each  tooth,  as  shown 
in  Figs.  305  and  306. 


Fig.  305. 


Fig.  306. 


The  cut  (Fig.  307)  shows  the  approximal,  labial,  and  lingual  faces  of 
a  superior  continuous-gum  central,  the  side  view  giving  the  position  and 
length  of  pin  and  the  inclination  of  the  labial  face.  Fig.  308  shows  the 
half  of  a  set  of  six  front  teeth  for  continuous-gum  work. 

In  burning  single  plain  teeth  it  has  been  observed  that  exceedingly 
small  specimens  vitrefy  more  quickly  and  are  more  liable  to  change  of 


Fig.  307. 


Fig.  308. 


form  from  over-burning  than  the  larger  ones.  To  avoid  accidents  of 
this  nature  it  has  been  recommended  that  the  small  be  separated  from 
the  larger  teeth,  and  that  each  lot  be  placed  upon  the  slide  and  burned 
separately. 


Fig.  309. 


Fig.  310. 


Fig.  311. 


Figs.   309-314,  show  some  of  the  unusual  forms  of  moulded   sec- 
tional   rubber    blocks,    in   which    considerable    improvement   has    been 


268 


MOULDING  AND  CARVING  PORCELAIN  TEETH. 


made  within  a  few  years.     These  are  made  in  a  variety  of  sizes  and 
degrees  of  curve. 


Fig.  312. 


Fig.  313. 


Fig.  314. 


Tinting  and  Staining  Porcelain  Teeth. 

Changes  may  be  made  in  the  color  or  shades  of  teeth,  or  devitalized 
and  discolored  teeth  may  be  imitated,  by  the  system  demonstrated  by 
Dr.  George  Cunningham  at  the  Columbian  Dental  Congress,  which 
consisted  in  the  application  of  a  set  of  paste  colors  or  the  stains  pre- 
pared and  furnished  by  Poulson  of  Dresden  or  Ash  Sons  of  London.* 

The  colors  usually  employed  in  china  painting  will  answer  very  well 
for  the  purpose,  and  a  small  selection,  consisting  of  sepia,  ivory  black, 
rose  pompadour  (gum  color),  ivory  yellow,  brown  yellow,  celestial  blue, 
and  relief  white  will  be  sufficient  with  which  to  form  almost  any  shade 
required  in  the  imitations  of  the  usual  discolorations  of  the  teeth  as  met 
with  in  the  natural  organs. 

The  implements  required  for  the  mixing  and  application  of  the  tints 
are  a  plain  glass  slab,  on  which  to  mix  the  colors  in  small  quantities ;  a 
small  palette  knife ;  a  small,  short-bristled  brush  for  stippling  or  spread- 
ing the  color,  such  as  can  readily  be  formed  by  cutting  off  the  bristles 
of  a  camel' s-hair  or  sable  brush,  so  that  the  remainder  is  short,  stubby, 
and  square  at  its  end ;  alcohol,  with  which  to  clean  the  teeth ;  brushes ; 
oil  of  cloves,  oil  of  lavender,  or  turpentine  to  thin  the  paints  to  proper 
consistence. 

The  grays,  yellows,  and  browns  are  the  tints  most  frequently  required 
in  imitating  the  discolorations  of  the  natural  teeth.  Ivory  black  is  of 
course  not  to  be  used  by  itself,  but  it  is  indispensable  as  a  means  of 
deepening  the  color  of  the  grays  and  browns. 

In  the  use  and  application  of  pigments  for  the  purpose  of  staining 
porcelain  teeth  the  operator  should  study  the  colors  of  the  natural 
organs  as  met  with  in  the  mouths  of  patients,  and  he  should  acquire 
experience  in  noting  the  effect  of  admixture  of  the  pigments  when 
applied  to  porcelain  teeth.  This  is  essential,  as  the  colors  when  devel- 
oped by  exposure  to  high  temperatures  are  not  always  of  the  degree  and 
shade  expected.  A  few  experiments,  which  can  easily  be  made  upon 
odd  teeth  by  means  of  the  Downie  or  Custer  furnace,  will  enable  the 
operator  to  apply  the  colors  with  some  degree  of  certainty. 


^  From  paper  on  "  Artistic  Staining  of  Artificial  Teeth  "  in  Ohio  Dental  Journal,  by 
Dr.  George  H.  Wilson  of  Cleveland,  Ohio. 


TINTING  AND  STAINING   PORCELAIN  TEETH.  269 

The  occasions  requiring  tinting  or  staining  are  not  numerous,  and  the 
system  should  be  applied  with  taste  and  judgment.  These  occasions  are 
found  in  cases  where  it  is  necessary  to  imitate  the  discoloration  of  a 
devitalized  tooth  ;  to  deepen  the  color  of  the  cuspids ;  to  imitate  the  dis- 
coloration of  the  dentine  left  bare  by  the  recession  of  the  gums ;  to  darken 
the  dentine  between  the  plates  of  enamel  on  the  cutting  edges  of  the 
teeth  of  elderly  subjects ;  to  imitate  the  opaque  or  white  spots  in  the 
enamel  of  incisors  or  cuspids,  or  the  yellow  spots  occasionally  seen  on  the 
surfaces  of  the  incisors. 

In  applying  the  stains  the  tooth  should  be  thoroughly  cleaned  with 
alcohol,  dried,  and  held  by  the  pins  with  a  pair  of  pliers  :  the  color  is 
mixed  with  oil  of  cloves  or  lavender  and  applied  with  a  cameFs-hair 
pencil,  the  quantity  or  thickness  being  governed  by  the  depth  of  shade 
required. 

The  color  is  fixed  by  subjecting  the  teeth  to  a  temperature  of  about 
2000°  F.  The  firing  may  be  satisfactorily  accomplished  in  either  of  the 
furnaces  above  named,  or,  as  described  by  Dr.  George  H.  Wilson,  "  by 
shaping  a  piece  of  No.  36  platinum  plate  so  as  to  cover  and  enclose  the 
teeth,  except  on  one  side,  which  is  left  open  as  a  peep-hole.  This 
miniature  oven  or  furnace  containing  the  teeth  is  placed  over  the  Bunsen 
burner  for  about  five  minutes,  when  the  flame  from  the  blowpipe  is 
placed  against  the  outside  of  the  clay  slab,  upon  which  it  is  held,  and 
gradually  bringing  it  over  upon  the  top  of  the  platinum,"  two  minutes' 
work  of  the  blowpipe  being  sufficient  to  vitrefy  and  fix  the  colors. 
''  Atrophy  and  worn  conditions  are  imitated  by  grinding  and  then  stain- 
ing." Gum  colors  are  formed  by  the  use  of  the  rose  pompadour,  the 
depth  of  the  shade  being  secured  by  varying  the  amount  of  the  relief 
white. 


CHAPTER  V. 

THE  PREPARATION  OF   THE  MOUTH;    CHOICE  OF 
MATERIAL  AND  TYPE  OF  DENTURE. 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 


When  it  is  considered  that  artificial  dentures  are  designed  to  restore 
the  partially  lost  function  of  mastication,  together  with  the  appearance 
possessed  by  the  mouth  when  the  natural  teeth  were  in  position,  it  is 
evident  that  we  have  several  important  matters  for  consideration — the 
furnishing  of  a  surface  which  shall  afford  the  necessary  support  to  the 
denture,  the  replacement  of  the  organs  of  mastication,  and  the  restora- 
tion of  the  facial  expression. 

The  natural  gums  themselves,  Avhen  in  a  normal  condition,  form  dense, 
fibrous,  elastic,  and  insensitive  pads  which  may,  without  discomfort  to  the 
individual,  be  subjected  to  considerable  pressure.  If  the  gums  become 
hypersemic  or  inflamed,  their  sensitivity  is  increased ;  there  is  an  inter- 
cellular infiltration  of  fluids  into  the  submucosa  ;  the  epithelial  covering- 
becomes  sodden  ;  the  structures  furnish  a  yielding  instead  of  a  firm 
base  for  the  support  of  a  plate.  It  is  obvious,  therefore,  that  where  a 
morbid  condition  exists  its  cause  is  to  be  sought  out  and  remedied. 

Morbid  Conditions  of  the  G-ums. — The  general  condition  of  hyper- 
semia  of  the  mouth  will  be  found  frequently  associated  with  more  or  less 
inflammation  of  the  pharynx  and  certain  forms  of  gastric  disorders, 
notably  irritative  dyspepsia.  This  oral  condition  will  be  commonly 
noted  in  spirit-drinkers  and  confirmed  smokers.  The  first  step  toward 
its  cure  is  to  remove  these  exciting  causes :  the  use  of  spirits  is  to  be 
interdicted  and  the  smoking  lessened  if  not  discontinued. 

It  is  not  infrequently  found  that  the  dyspepsia  itself  is  traceable  to 
the  loss  of  the  masticatory  apparatus,  the  patient  bolting  food  or  pre- 
senting to  the  stomach  masses  much  larger  than  can  be  perfectly  digested. 
While  in  actual  practice  few  of  these  conditions  receive  consideration  at 
the  hands  of  the  prosthetist,  it  is  undoubtedly  advisable  that  they  should 
be  corrected  in  order  to  bring  the  oral  structures  to  a  normal  condition. 

In  the  condition  due  to  non-mastication  of  food  the  gastric  symptoms 
and  oral  disorders  arising  from  tliem  are  usually  relieved  through  the 
use,  for  a  period,  of  soft  foods  and  the  internal  administration  of — 

I^i.  Bismuth,  subnit.,  gr.  x  ; 

Acid,  carbolic,  gr.  f  ; 

Sodii  bicarb.,  gr.  x. 

M.  et  ft.  pulv.  (i). 
Sig.  To  be  taken  two  hours  after  meals. 

270 


RETENTION  OR   EXTRACTION  OF  NATURAL   TEETH.  271 

The  intestinal  functions  are  to  be  regulated  through  the  administration 
of  mild  saline  aperients.  Where  the  symptoms  are  those  of  chronic  gas- 
tric catarrh  and  of  fermentation  of  food-masses,  discomfort  during  diges- 
tion, burning  eructations,  and  occasional  sharp  pains  which  last  during 
the  slow  digestion,  the  silver  salts  are  efficacious.  To  allay  the  pain  a 
sedative  is  indicated,  but,  as  many  of  these  cases  are  attended  by  con- 
stipation, opium  is  contraindicated  and  belladonna  or  hyoscyamus 
substituted. 

I^.  Argenti  oxidi,  gr,  v  ; 

Ext.  hyoscyami,  gr.  v. 

M.  et  ft.  pil.  No.  X. 
Sig.  One  pill  three  times  a  day  before  meals  (Bartholow). 

The  mouth  is  to  be  washed  periodically  with  some  mild  astringent 
antiseptic,  such  as  borine,  listerine. 

If  there  are  marked  symptoms  of  stomatitis,  probably  the  most 
effective  mouth-lavage  is  a  solution  of  potassic  chlorate,  gr.  xv-sj. 
Starchy  and  fatty  articles  of  food  are  to  be  omitted  from  the  dietary  for 
the  time  being,  as  they  undergo  fermentative  changes  in  the  stomach. 
The  local  maniifestations  are  to  receive  appropriate  treatment. 

Stomatitis  itself  may  be  due  to  a  variety  of  causes  ;  any  cause,  in  fact, 
which  lessens  the  general  bodily  tone  may  determine  it.  When  it  ap- 
pears as  small  ulcers,  these  are  touched  with  pure  carbolic  acid,  and  then 
usually  take  care  of  themselves.  Their  recurrence  may  be  usually  pre- 
vented through  the  internal  administration  of  I^.  Acid,  hydroch.  dil.,  gtt. 
V. — S.  Immediately  after  meals,  well  diluted.  If  the  ulceration  is  dif- 
fused, a  spray  of  hydrogen  peroxide,  followed  by  one  of  a  solution  of 
potassium  chlorate,  will  be  found  efficacious.  Mercurial  stomatitis  may 
be  cured  by  tlie  same  local  applications.  In  short,  the  several  causes  of 
stomatitis  are  to  be  sought  out  and  removed. 

Gingivitis  or  ulitis,  characterized  by  a  boggy  condition  of  the  gums, 
may  arise  from  a  variety  of  causes  :  those  specifically  demanding  the  aid 
of  the  dental  practitioner  are  due  to  the  presence  of  salivary  calculi 
about  the  natural  teeth,  to  extension  of  chronic  inflammatory  processes 
from  the  roots  of  necrosed  or  partially  necrosed  teeth,  or,  again,  to  any 
stage  of  the  process  known  as  pyorrhoea  alveolaris,  including  under  this 
head  all  of  those  inflammatory  degenerations  which  lead  to  the  gradual 
exfoliation  of  the  teeth. 

Scurvy  is  a  malady  so  rare  as  to  scarcely  require  mention  in  this  con- 
nection. 

Retention  or  Extraction  of  Natural  Teeth. — When  a  case  presents 
for  an  artificial  denture,  if  the  mouth  be  edentulous  and  the  condition  of 
the  gums  normal,  the  preliminary  steps  in  the  construction  of  a  denture 
may  be  taken.  If,  as  commonly  found,  there  are  present  natural  teeth 
or  roots,  it  is  to  be  determined,  first,  which  of  these  shall  be  retained 
and  which  extracted.  It  is  to  be  remembered  that,  although  the  gen- 
eral removal  of  isolated  teeth  may  render  more  simple  and  easy  the 
adaptation  of  an  artificial  denture,  the  latter  is  of  decidedly  less  value  to 
the  patient  than  are  natural  teeth.  Dr.  Black '  has  found  that  the  force 
a  patient  could  exert  upon  artificial  dentures  was  from  one-tenth  to  one- 

1  Cosmos,  1895. 


272  THE  PREPARATION  OF  THE  MOUTH,   ETC. 

fourth  that  exerted  by  the  natural  teeth,  the  force  of  the  former  not 
being  sufficient  to  crush  many  of  the  usual  articles  of  diet.  There  will 
be  seen  in  this  a  cause  of  the  dyspepsia  common  among  those  wearing 
artificial  dentures. 

Whether  to  retain  or  extract  roots  or  teeth  will  depend,  first,  upon 
the  possibility  of  readily  bringing  such  teeth  to  a  condition  of  health. 
A  general  rule  is  that  those  containing  vital  pulps  are  to  be  retained. 
Teeth  or  roots  in  which  there  is  evident  necrosis  of  the  pericementum 
are  immediately  removed,  as  they  are  an  incurable  source  of  inflamma- 
tion in  the  gum-tissues.  Roots  which  are  the  seat  of  pericemental  in- 
flammation are  to  receive  appropriate  treatment ;  if  they  do  not  respond, 
they  are  deemed  a  detriment  and  are  extracted.  If  retained,  they 
should  perform  service,  and  are  to  receive  artificial  crowns.  If  they  are 
not  sufficiently  strong  to  furnish  a  base  for  an  artificial  crown,  they  are, 
as  a  rule,  unfit  for  retention.  It  is  not  absolutely  essential  that  un- 
crowned roots  should  be  extracted,  but  their  presence  is  generally  a  hin- 
drance rather  than  an  aid.  Teeth  of  which  the  crowns  have  been  lost, 
if  brought  to  a  condition  of  health,  by  receiving  artificial  crowns  may  be 
made  to  furnish  acceptable  clasp  teeth. 

The  gums  about  vital  teeth  must  be  brought  to  a  condition  of  health. 
The  most  common  source  of  inflammation,  deposits  of  calculi  upon  the 
gums  and  beneath  the  margins,  must  be  thoroughly  removed,  and  the 
gums  receive  such  treatment  as  shall  render  them  firm  and  resistant,  the 
operator  painting  them  occasionally  with  dilute  tr.  iodine,  the  patient  to 
employ  an  astringent  and  antiseptic  wash  until  a  normal  condition 
obtains.  One  of  the  most  satisfactory  of  formulae  for  this  purpose  will 
be  found  in  a  wash  of — 

I^.  Zinc,  chlorid.,  gr.  v-x  ; 

Aquse,  sj. — M. 

Sig.  Its  use  continued  for  a  week. 

Should  the  tumefaction  of  the  gum-tissue  be  but  slight,  a  mildly  astrin- 
gent wash  suffices  : 


Sir 


^.  Ext.  hamamelis  virg., 

ij; 

Aquse, 

§vj 

Jsed  ad  libitum. 

-M. 


The  gradual  and  progressive  loss  of  teeth,  due  to  the  process  called 
pyorrhoea  alveolaris,  leaves  the  poorest  of  bases  for  an  artificial  denture. 
The  gradual  loss  of  the  alveolar  process  which  accompanies,  or  rather 
causes,  the  loss  of  the  teeth  leaves  the  condition  known  as  the  flat,  flabby 
arch.  The  resorption  is  confined  to  the  bony  tissues,  leaving  the  en- 
gorged soft  tissues  without  a  corresponding  diminution  of  volume.  It 
is  needless  to  emphasize  the  extreme  importance  of  checking  and  holding 
in  check  this  malady,  the  bUe  noir  of  dentistry. 

In  examining  the  palatal  vault  it  is  to  be  noted  whether  its  configu- 
ration is  such  as  to  militate  against  the  employment  of  a  chamber  plate. 
Are  there  protuberances  or  tuberosities  of  bone  occupying  a  portion  of 
the  vault  to  be  covered  by  the  vacuum  chamber  ?     In  that  event  it  is 


SURGICAL   COMPLICATIONS.  273 

doubly  desirable  that  clasp  support  be  obtained,  and  so  increased  signif- 
icance attaches  to  the  retention  of  such  roots  as  may  be  properly  crowned 
or  such  teeth  as  may  serve  for  clasp  attachment. 

The  question  frequently  arises  whether  or  not  to  extract  isolated  teeth 
which  are  healthy,  but  which  render  more  difficult  the  adaptation  of  an 
artificial  denture.  The  writer  advises  against  it  as  a  general  rule.  Such 
teeth  are  valuable  in  that  they  stay  the  bite.  In  occluding  they  limit 
the  amount  of  displacing  stress  brought  to  bear  upon  the  artificial  den- 
ture, and  thus  increase  its  actual  capability  of  service.  Such  teeth 
are  lost  sooner  or  later,  and  yet  they  may  remain  for  many  years. 
It  is  especially  desirable  that  the  cuspid  teeth  be  retained.  They  main- 
tain a  contour  at  the  canine  eminences  which  the  artificial  denture  does 
not  always  fully  restore  when  once  lost.  Even  the  roots  themselves 
should,  when  possible,  be  retained,  and  crowned  when  practicable. 

It  is  better,  as  a  general  rule,  to  retain  all  healthy  teeth  and  roots  : 
the  skill  of  the  operator  is  to  make  his  work  conform  to  conditions 
rather  than  alter  conditions  to  suit  his  convenience. 

A  solitary  tooth  remaining  in  the  upper  arch  necessitates  a  break  in 
the  general  plate  outline  detrimental  for  the  following  reason  :  The  gum 
upon  which  the  plate  rests  at  the  site  of  the  natural  tooth  undergoes 
absorption,  and  hence  a  space  develops  between  plate  and  gum  which 
permits  the  ingress  of  air  to  the  palatal  surface  of  the  plate  and  destroys 
atmospheric  adhesion.  Isolated  molars,  if  perfectly  firm,  are  to  be  per- 
mitted to  remain  ;  even  more,  in  many  cases  they  are  to  be  carefully  pre- 
served. If  there  be  one  on  either  side,  a  double  advantage  is  obtained  :  if 
the  future  denture  is  to  be  mounted  upon  a  vulcanite  plate,  the  latter, 
embracing  these  natural  teeth,  has  an  additional  source  of  support ;  if 
mounted  upon  metallic  plates,  these  teeth  furnish  means  of  clasp  attach- 
ment. 

In  the  lower  jaw  teeth  which  stand  in  a  column  of  two  or  more  than 
two  should  nearly  always  be  retained.  Isolated  teeth  are  to  be  retained 
when  they  can  possibly  be  made  to  serve  as  clasp  teeth.  Lower  den- 
tures, depending  almost  entirely  upon  weight  to  keep  them  in  position, 
need  clasp  support  whenever  admissible.  Even  a  solitary  bicuspid 
should  usually  be  retained,  and  if  one  on  either  side  can  be  retained  the 
patient  is  immeasurably  the  gainer. 

A  solitary  inferior  incisor  is  to  be  extracted  :  the  writer  also  advises 
the  extraction  of  a  superior  lateral  incisor  when  the  latter  is  the  only 
tooth  remaining.  It  will  not  remain  long  enough  to  be  of  any  actual 
service,  while  a  central  may  last  much  longer  ;  but  even  a  central  inci- 
sor, except  under  unusual  circumstances,  when  it  is  the  solitary  tooth  of 
an  arch,  had  better  be  extracted. 

Surgical  Gomplications. — The  length  of  time  to  elapse  between  the 
extraction  of  teeth  and  the  insertion  of  artificial  teeth  varies  with  the 
existing  conditions.  After  the  forcible  removal  of  a  firmly  implanted 
tooth  there  is  more  or  less  inflammatory  swelling  of  the  soft  tissues.  A 
plate  or  tooth  adapted  to  such  a  place  during  the  height  of  the  swell- 
ing would  have  its  relation  to  the  gum  altered  as  soon  as  the 
swelling  has  disappeared.  It  is  the  general  rule,  therefore,  to  await  the 
subsidence  of  the  inflammatory  swelling  before  taking  an  impression. 
Should  it  be  that  it  is  imperative  to  insert  the  artificial  teeth  immediately 

18 


274  THE  PREPARATION  OF  THE  MOUTH,  ETC. 

upon  the  extraction  of  the  natural  organs,  due  allowance  is  to  be  made 
for  the  inevitable  swelling  and  subsequent  shrinkage.  Succeeding  the 
latter  wall  be  a  resorption  of  the  alveolar  process,  which  varies  widely  its 
extent  according  to  the  individual  and  the  local  conditions. 

In  very  rare  instances  the  following  condition  may  be  found  :  At 
some  point  a  cicatricial  adhesion  has  occurred  between  the  mucosa  of  the 
cheek  and  that  of  the  alveolar  wall.  This  may  be  a  cord-like  attach- 
ment which  marks  the  site  of  the  fistulous  opening  of  a  previous  abscess  ; 
the  point  of  the  attachment  may  be  at  any  part  of  the  alveolar  wall. 
Unless  it  should  be  at  the  level  with  the  top  of  the  alveolar  arch,  it  will 
not  disturb  the  stability  of  an  artificial  denture  and  calls  for  no  inter- 
ference. Should  its  attachment  be  at  or  beyond  the  height  of  the  ridge, 
operative  measures  are  indicated,  as  the  movements  of  the  cheek  trans- 
mitted through  the  cord  would  displace  a  fixture. 

Wounds  of  this  part  of  the  mouth,  whether  incised  or  from  injuries 
by  caustics,  may  in  healing  cause  extensive  attachment  of  the  cheek 
to  the  alveolar  wall,  and  render  the  wearing  of  a  plate  difficult  if  not 
impossible.  The  surgical  principle  involved  in  correcting  the  condition 
is  a  separation  of  the  attachment  and  preventing  adhesion  of  the  cut 
surfaces  until  perfect  cicatrization  has  occurred. 

An  impression  of  the  mouth  is  taken  and  a  model  made.  (See  Chap- 
ters VIII.  and  IX.)  At  the  site  of  the  adhesion  represented  on  the 
model  the  latter  is  cut  away  to  the  usual  plate  depth,  leaving  the  model 
more  prominent  than  anatomically  correct,  so  that  there  shall  be  no 
pressure  by  a  plate  upon  the  alveolar  wall.  A  plate  of  vulcanite  is 
constructed  upon  the  model,  its  edges  rounded,  smoothed,  and  the  entire 
piece  highly  polished.  When  this  is  finished  the  mouth  is  thoroughly 
sterilized  and  painted  with  a  10  per  cent,  solution  of  cocaine ;  the  cheek 
is  drawn  away  from  the  alveolar  wall,  making  the  tissues  tense,  and  a 
sharp  bistoury  is  used  to  divide  the  attachment,  the  cut  to  be  made  in 
the  middle  of  the  attaching  tissue.  A  styptic  applied  or  a  spray  of 
hydrogen  peroxide  usually  checks  the  hemorrhage.  The  cut  surfaces 
are  dried  by  means  of  lint,  both  are  painted  with  a  solution  of  styptic 
collodion,  and  as  soon  as  this  has  dried  the  plate  is  inserted.  The  anti- 
septic varnish  called  steresol  is  an  admirable  covering  for  these  as  for 
any  wounds  about  the  mouth.  The  patient  is  directed  to  wash  the 
mouth  several  times  a  day  with  an  antiseptic  such  as  borine,  listerine, 
borolyptol,  etc.,  and  the  case,  if  the  person  be  healthy,  should  rapidly 
proceed  to  cure.  Should  the  granulating  surfaces  become  unhealthy- 
looking,  they  are  to  be  washed  or  painted  with  a  solution  of  silver 
nitrate,  gr.  iv-gj.  The  plate  is  worn  until  healing  is  complete,  usually 
in  about  two  weeks,  when  an  impression  for  a  denture  may  be  taken. 

Choice  of  Base. — In  the  mouths  of  patients  who  have  worn  arti- 
ficial dentures  it  will  be  found  not  infrequently  that  the  tissues  under- 
lying the  plates  are  in  a  condition  of  hyperemia  or  even  marked  con- 
gestion. While  this  condition  is  more  common  under  plates  of  vulcanite 
than  under  those  made  of  metal,  it  is  occasionally  found  under  the  latter 
class  of  plates.  It  is  most  usual  under  vulcanite  plates  which  are  im- 
properly finished  on  the  palatal  surface,  the  roughness  of  the  latter 
acting  as  an  irritant  to  the  soft  tissues.  In  the  degree  that  plates  of 
this  base  are  highly  finished  there  is  a  lessening  of  what  is  called  rubber 


USE  OF  CLASPS.  275 

sore  mouth.  Lack  of  cleanliness  upon  the  part  of  a  patient  is  a  prolific 
source  of  the  hypersemia.  Deposits  of  food-debris,  being  permitted 
to  remain  upon  the  plate,  undergo  fermentative  and  putrefactive  de- 
composition, the  products  of  which  act  as  irritants.  Aside  from  vascular 
injection  of  the  soft  parts  due  to  these  palpable  sources  of  irritation, 
instances  are  seen  where  the  wearing  of  a  vulcanite  plate,  no  matter 
how  carefully  finished  or  cleansed,  is  attended  by  hypersemia  of  the 
underlying  tissues.  In  lieu  of  a  better  explanation  this  condition  is 
ascribed  to  lack  of  conductivity  of  the  base.  This  view  becomes  more 
plausible  when  it  is  seen  that  a  plate  constructed  of  a  good  conductor  (of 
metal)  may  be  worn  without  causing  the  effects  noted  under  plates  of 
vulcanite. 

Vacuum  chambers  which  are  too  deep  and  which  have  too  sharp 
edges  are  a  source  of  irritation.  Therefore,  where  an  artificial  denture 
upon  a  vulcanite  base  is  presented  for  examination,  complaint  being 
made  by  the  patient  of  soreness  of  the  parts  enclosed  by  it  an  examina- 
tion is  made  to  note  the  position  of  the  irritated  areas.  If  due  to  the 
cutting  of  the  air-chamber,  the  edges  of  the  latter  must  be  smoothed 
and  the  chamber  partially  obliterated  by  placing  a  thin  layer  of  paraffin 
and  wax  in  it.  Should  the  plate  be  rough  itself  or  contain  foreign  sub- 
stances, it  is  washed  with  a  strong  antiseptic.  The  writer  lays  the  plates 
in  a  10  per  cent,  solution  of  sodium  peroxide ;  they  are  then  rinsed  in  a 
5  per  cent,  solution  of  sulphuric  acid,  scrubbed,  and  their  palatal  surface 
brushed  with  pumice  and  stiff  brushes. 

Where  and  when  a  choice  of  base  is  admissible  gold  is  as  much  king 
in  prosthetic  as  it  is  in  operative  dentistry.  A  general  rule  for  its  em- 
ployment, based  upon  the  cases  or  classes  of  cases  in  which  it  is  found 
to  serve  best,  would  be  as  follows  :  It  is  the  only  material  in  present  use 
which  meets  all  the  indications  for  a  proper  base  for  all  partial  dentures. 

In  full  cases  gold  or  continuous  gum  is  the  choice.  It  may  be  given 
as  a  principle  that  the  tissues  of  the  mouth  prefer  the  contact  of  a  metal 
surface  to  that  of  one  of  the  vegetable  bases ;  so  that  in  all  cases  where, 
by  the  experience  of  the  patient,  the  weight  of  a  perfectly  fitted  denture 
is  not  urged  against  gold  or  continuous  gum,  these  latter  are  to  be  pre- 
ferred. In  lower  cases,  where  weight  is  an  advantage,  this  feature  doubly 
recommends  the  metallic  base.  Vulcanite  serves  best  in  mouths  having 
firm  gum-tissues,  a  high  vault,  and  where  the  bulk  of  the  piece  is 
unusually  great,  and  in  which  the  plate  adhesion  has  been  demonstrated 
to  be  weak.  Flat  mouths,  with  flabby  tissues,  bear  metal  better  than 
they  do  vulcanite.  Continuous-gum  dentures  serve  best  in  what  woidd 
be  termed  vaults  of  the  average  depth,  moderately  high  alveolar  walls, 
and  where  a  greater  bulk  of  material  is  required  to  restore  lost  form  than 
can  be  had  with  gold  plates.  When  accurately  adapted,  continuous-gum 
dentures  serve  admirably  as  full  lower  cases. 

Use  of  Clasps. — The  question  of  the  use  of  clasps  is  determined  by 
necessity.  They  are,  as  a  general  rule,  attached  to  all  partial  lower  den- 
tures where  practicable.  When  an  option  is  admissible,  they  are  not 
attached  to  the  class  or  varieties  of  teeth  which  are  seen  to  be  susceptible 
to  dental  caries.  If  sufficient  stability  can  be  secured  without  their  use, 
they  are  not  employed.  This,  however,  necessitates  that  a  plate  shall  be 
large  enough  to  serve  as  a  stable  base,  one  which  is  unnecessarily  large 


276  THE  PREPARATION  OF  THE  MOUTH,   ETC. 

for  carrying  one  or  two  teeth,  so  that  small  plates  supporting  very  few 
teeth  are  frequently  mounted  upon  small  plates,  and  have  their  attach- 
ment through  the  medium  of  clasps. 

Type  of  Denture. — Where  the  configuration  of  the  vault  is  of  such 
form  that  a  median  vacuum  chamber  is  inadmissible,  owing  to  the  pres- 
ence of  tuberosities  which  cover  the  median  line  of  the  vault,  what  is 
known  as  a  horseshoe  chamber  is  tested  :  if  this  prove  insufficient,  two 
distinct  lateral  chambers,  occupying  respectively  areas  upon  the  right 
and  left  lateral  aspects  of  the  plates,  may  used.  It  is  in  such  cases  that 
natural  teeth  should  be  preserved  to  serve  as  clasp  attachments  should 
attempts  to  secure  adhesion  by  means  of  the  chambers  prove  unavailing. 
For  the  same  reason  roots  are  retained  which  may  serve  as  the  bases  for 
artificial  crowns,  to  which  clasps  may  be  fitted. 

Cast  or  swaged  aluminum  dentures  serve  best  in  those  shapes  of 
vault  and  alveolar  walls  in  which  vulcanite  renders  good  service,  and 
in  mouths  apparently  irritated  by  the  presence  of  a  vulcanite  plate  may 
be  advantageously  substituted  for  the  latter  base. 

In  regard  to  the  choice  between  bridge-work  and  partial  plates,  if  the 
conditions  present  permit  the  ready  placement  of  a  properly  designed 
bridge,  with  a  probability  of  its  permanent  usefulness,  it  is  selected ; 
otherwise  the  indication  for  a  plate  denture  prevails.  The  direct  indica- 
tions for  a  bridge  are  a  loss  of  teeth  between  others  which  have  sound 
and  firmly  fixed  roots,  and  preferably  those  which  require  no  mutilation 
to  fit  them  to  serve  as  abutments ;  little  or  no  loss  of  gum-contour  at  the 
sites  of  the  absent  teeth ;  an  articulation  of  a  type  which  shall  permit 
the  placing  of  perfectly  protected  porcelain  facings,  which  shall  meet  all 
requirements  as  to  restoration  of  appearance ;  the  spaces  beneath  the 
body  of  the  bridge  to  be  accessible  to  tooth-brushes.  The  introduction  of 
removable  bridge-work  has  eliminated  many  of  the  objections  urged 
against  this  class  of  fixture.  In  addition,  what  are  known  as  detach- 
able plate-bridges  remove  other  objections  to  the  general  class  of  bridge- 
work  ;  but  the  judgment  of  the  conservative  operator  still  finds  many 
cases  in  which  partial  plate  dentures  are  the  rational  indication  and 
bridge-work  clearly  contraindicated. 


CHAPTER   VI. 

TAKING  IMPRESSIONS  OF  THE  MOUTH. 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 


Taking  an  impression  of  the  mouth  is  an  operation  of  such  apparent 
simplicity  as  to  seem  to  require  but  brief  description,  and  yet  it  is  one 
which  is  as  rarely  done  well  as  any  operation  in  the  practice  of  dentistry. 
It  is  absolutely  necessary  for  the  proper  adaptation  of  an  artificial  denture 
that  this,  the  primary  step  in  its  construction,  be  accomplished  with  an 
accuracy  which  shall  eliminate  any  faults  of  the  denture  traceable  to  an 
inaccurate  impression. 

The  operation  consists  in  securing  a  perfect  imprint  of  the  jaw  in 
some  soft  substance  which  by  its  hardening  will  retain  the  impression 
made  in  it.  The  impression  material  is  conveyed  to  position  and  confined 
by  means  of  an  appropriately-shaped  tray. 

Materials  Employed. — There  are  two  classes  of  impression  material 
in  general  use  :  first,  those  which  are  softened  by  heat  and  harden  in 
cooling  ;  second,  those  made  into  a  paste  with  water,  the  paste  hardening 
through  crystallization.  The  first  class  includes  beeswax  and  prepara- 
tions made  of  it,  such  as  wax  and  paraffin,  wax  and  gutta-percha ;  next 
modelling  compound,  a  mixture  of  gum  copal,  stearin,  and  French  chalk  ;^ 
lastly,  gutta-percha.  The  second  class  includes  plaster  of  Paris  and  the 
various  mixtures  made  with  it  as  a  basis. 

Plaster  of  Paris  when  in  a  condition  of  paste  is  perfectly  adaptable  to 
any  surface,  no  matter  how  irregular  the  latter  may  be,  and  causes  no 
displacement  of  parts  or  alteration  of  their  positions.  When  set  it 
possesses  such  rigidity  that  its  withdrawal  from  undercuts  is  impossible 
without  fracture  of  the  mass  or  yielding  of  the  parts  enclosed  by  it.  In 
setting  the  mass  expands  about  one  five-hundredth  of  its  volume.  It  is 
said  not  to  expand  when  sodium  chloride  or  potassium  sulphate  is  added 
to  the  paste.  (For  the  chemical  and  physical  properties  of  plaster,  its 
preparation  and  treatment,  see  Chapter  I.  page  22.) 

Beestoax. — The  special  advantages  of  wax  are  that  it  is  easily  manip- 
ulated, is  inelastic,  and  contracts  but  slightly  in  cooling.  The  disadvan- 
tages are — the  pressure  required  to  adapt  it  forces  all  the  soft  parts  out 
of  normal  position,  and  renders  the  taking  of  a  perfect  impression  of 
some  mouths  with  it  impossible  ;  the  tendency  to  distortion  of  its  form 

^  Dr.  J.  W.  White,  "Taking  Impressions  of  the  Mouth." 

277 


278  TAKING  IMPRESSIONS  OF  THE  MOUTH. 

in  withdrawing  is  also  a  serious  objection  to  its  use.  It  does  not  give 
as  accurate  an  impression  as  plaster,  but  still  is  preferred  by  some  ope- 
rators. 

When  wax  is  used,  either  a  pure  specimen  should  be  obtained  or  one 
which  has  been  judiciously  combined  with  a  foreign  substance  for  a  spe- 
cific purpose.  Commercial  adulterations  with  tallow,  resin,  vegetable 
wax,  etc.  injure  it,  making  it  difficult  to  manage.  White  wax  has  an 
advantage  over  the  yellow  in  that  it  does  not  draw  out  of  shape  so 
readily,  and  there  is  consequently  less  liability  to  have  the  impression 
distorted  than  with  yellow  wax.  It  takes  a  sharper  impression  than 
the  yellow  variety,  but  it  is  more  difficult  to  bring  to  the  required 
plasticity,  and  more  force  is  required  to  obtain  a  correct  impression 
unless  the  wax  is  made  hot.  In  summer-time  the  additional  hardness 
is  in  its  favor. 

Scrap  wax  of  either  variety  should  never  be  used  without  remelt- 
ing,  as  it  is  difficult,  if  not  impossible,  to  get  it  into  a  homogeneous 
mass. 

Paraffin  is  frequently  added  to  wax,  >and  imparts  to  it  the  property  of 
becoming  plastic  at  a  lower  temperature.  A  small  proportion  improves 
it,  especially  for  use  in  cold  weather,  but  if  in  excess  it  causes  the  wax 
to  separate  into  layers  which  are  not  easily  reunited.  It  take  a  sharper 
impression  than  wax  alone,  with  less  liability  of  drawing  out  of  form,  the 
addition  of  the  paraffin  in  proper  quantity  causing  the  composition  to  be 
harder  when  cold  than  the  wax  alone.  A  combination  of  wax  and  gutta- 
percha is  used  and  highly  prized  by  some,  on  account  of  its  toughness. 
The  objection  to  it  is  that  it  is  sticky.  It  may  adhere  to  the  plaster  in 
making  a  model  unless  previously  varnished. 

The  other  plastic  materials  will  be  described  together  with  methods 
of  manipulation. 

Impression  Trays. — Impression  trays  are  receptacles  designed  to 
carry  impression  material  into  position  in  the  mouth,  to  retain  it  while 
there,  and  to  hold  the  form  of  the  impression  during  and  after  its 
removal  from  the  mouth. 

Properly  shaped,  a  tray  should  represent  in  form  the  particular  jaw 
of  which  an  impression  is  to  be  taken,  to  be  only  sufficiently  larger  than 
the  jaw  to  have  the  volume  of  the  impression  material  great  enough  to 
hold  together  in  a  common  mass.  For  the  majority  of  cases,  and  with 
any  of  the  materials  employed  in  impression-taking,  this  would  require 
a  cup  to  be  about  one-quarter  inch  or  less  larger  in  all  respects  than  the 
parts  it  is  to  embrace. 

The  well-equipped  laboratory  should  be  provided  with  an  extensive 
set  of  trays  as  furnished  by  the  manufiicturer  to  meet  the  needs  of  the 
majority  of  cases. 

Figs.  315  and  316  show  the  class  of  trays  designed  for  the  taking 
of  full  upper  impressions.  Three  sizes  will  usually  be  found  to  meet 
general  requirements. 

Cups  especially  designed  for  use  with  plaster  are  illustrated  in  Fig. 
316.  These  cups,  made  of  britannia  metal,  may  be  filed,  cut,  or  bent  to 
conform  to  irregularities  of  arch  outline  or  palatal  vault,  so  that  the 
tray  shall  be  uniformly  one-quarter  inch  larger  than  the  parts  it  is  to 
enclose. 


IMPRESSION  TRAYS. 


279 


Figs.  317  and  318  illustrate  the  trays  designed  for  the  taking  of  full 
lower  impressions.     These  frequently  require  alteration  of  form  by  bend- 


FiG.  315. 


Fig.  316. 


Fig.  317. 


ing  and  cutting.  It  is  necessary  that  lower  trays  should  have  their  edges 
and  outlines  conform  to  those  of  the  jaw,  for  assurance  that  the  im- 
pression material  shall  be  properly  carried  into  position. 


280  TAKING  IMPRESSIONS   OF  THE  MOUTH. 

For  partial  upper  dentures  the  form  of  tray  shown  in   Fig,  319  will 
be  found  generally  applicable.     To  ensure  a  closer  adaptation   of  the 

Fig.  318. 


tray  to  the  vault  and  alveolar  wall  an  adjustable  tray  (Fig.  320)  is  em- 
ployed when  indicated. 


Fig.  319. 


For  a  common  class  of  partial  lower  impressions  a  tray  of  the  general 
form  of  Fig.  321  is  employed,  the  edges  of  which  shall  extend  at  all 
points  deeper  than  the  plate  line. 

Where  the  remaining  natural  teeth  are  scattered,  trays  of  the  forms 
Figs.  322  and  324  are  usually  employed— Fig.  322  where  the  crowns  of 


IMPRESSION  TRAYS. 


281 


the  teeth  are  short ;  Fig.  324  when  they  are  long.     The  adjustable  tray, 
Kg.  322,  may  be  adapted  to  different  arch  outlines. 


Fig.  320. 


Fig.  321. 


The  impression  trays  as  they  are  received   from  the  manufacturer, 
while  adapted  for  tlie  taking  of  impressions  of  the  majority  of  cases,  are 


282 


TAKING  IMPRESSIONS  OF  THE  MOUTH. 


frequently  found  to  require  alteration  of  their  forms  or  outlines  to  adapt 
them  to  odd  cases. 

The  requirements  of  a  proper  cup,  that  its  outline  shall  embrace  more 


Fig.  323. 


Fig.  324. 


of  the  jaw  than  is  to  be  covered  by  the  plate,  and  to  be  at  all  points  about 
a  quarter  of  an  inch  larger  than  the  jaw,  show  that  many  cups  in  their 


IMPRESSION  TRAYS. 


283 


original  forms  are  not  correctly  applicable.  It  may  be  that  a  close  cor- 
respondence between  the  tray  and  alveolar  arches  is  not  to  be  had  in  the 
original  form  of  the  tray,  or,  again,  some  portions  of  the  edge  of  the  tray 
may  impinge  upon  the  frsena  or  upon  the  mucous  membrane  reflected 
from  the  cheek  or  lips. 

In  adapting  trays  to  full  dentures  the  former  are  to  be  bent  by  means 
of  pliers  when  it  is  necessary  to  alter  their  outlines  to  conform  with  those 
of  the  alveolar  arch.  Any  edges  of  the  tray  which  may  impinge  upon 
the  soft  tissues  are  dressed  down  by  means  of  shears  and  flies  until  a 
proper  adaptation  is  secured.  Heavy  plate-nippers  are  employed  to  cut 
out  the  tray  about  the  site  of  a  frsenum.  The  cut  edges  should  be  rounded 
and  smoothed  before  the  impression  is  taken. 

The  necessary  changes  to  a  tray  for  a  full  denture  are  best  or  most 
accurately  made  by  forming  a  plaster  model  in  a  wax  impression,  then 
by  means  of  pliers,  flies,  shears,  nippers,  and  the  horn  mallet  bring  an 
approximate  tray  into  the  correct  position  of  about  one-fourth  of  an  inch 
larger  at  all  points  and  parts  than  the  model. 

Fig.  325. 


Special  Trays. — It  is  occasionally  found — more  frequently  in  such 
partial  lower  cases  as  is  illustrated  by  Fig.  325 — that  none  of  the  ready- 
made  trays  can  be  altered  sufficiently  to  form  a  correct  tray.  It  may  be 
necessary  to  make  a  special  tray.     A  large  wax  impression  is  taken  and 


Fig.  326. 


a  plaster  cast  poured.     The  cast  is  warmed,  and  covered  completely,  at 
the  portions  to  be  embraced  by  the  cup,  by  a  layer  of  wax  at  least  one- 


284  TAKING   IMPRESSIONS  OF  THE  MOUTH. 

quarter  of  an  inch  thick.  The  wax  is  made  thicker  about  the  necks  of  the 
teeth — about  half  an  inch  thick  or  more ;  small  spaces  between  neighbor- 
ing teeth  are  to  be  filled  flush  with  the  general  surface  of  the  wax. 

A  heavy  zinc  die  and  counter-die  are  made,  as  described  in  Chapter 
X.,  and  a  piece  of  sheet  brass  No.  22  is  swaged  to  cover  as  much  of  the 
die  as  should  be  embraced  in  the  impression  cup.  A  long  strip  of  the 
same  metal  doubled  on  itself  serves  as  a  handle ;  this  may  be  attached 
by  means  of  a  soft  solder. 

The  principle  embodied  in  the  following  method  is  one  of  wide  appli- 
cation— viz.  that  the  plaster  covering  the  vault  and  arch  should  be  of 
uniform  thickness,  and  to  ensure  that  it  shall  be  carried  into  position  in 
such  a  layer  it  is  necessary  that  the  cup  should  be  properly  adapted  to 
that  end. 

Dr.  J.  B.  Bean's  Method  of  Preparing  Trays  and  Taking  Impressions. — 
A  wax  impression  of  the  arch  and  vault  are  taken,  and  a  plaster  model 
made  :  over  all  of  the  surface  to  be  embraced  by  the  future  plate,  and 
for  about  half  an  inch  beyond  it  at  all  points,  a  layer  of  wax  having  a 
uniform  thickness  of  about  one-eighth  of  an  inch  or  more  is  placed.  Dies 
and  counter-dies  are  formed,  between  which  a  stout  brass  plate  is  swaged. 
The  tray  is  thrown  into  nitrous  acid,  washed  in  soap  and  water,  and  dried 
in  sawdust,  which  develops  a  surface  resembling  frosted  gold. 

The  tray  is  heated  and  two  coats  of  thick  shellac  varnish  are  applied 
(the  tray  is  lacquered).  While  the  shellac  is  soft  a  ball  of  cotton  is 
pressed  into  the  interior  of  the  tray,  and  when  the  lacquer  has  hardened 
the  cotton  is  drawn  away,  leaving  small  tufts  which  have  been  caught 
and  retained  by  the  shellac. 

The  impression  is  taken  in  plaster  :  the  small  volume  of  the  latter  lessens 
any  tendency  to  nausea,  and  its  even  distribution  equalizes  any  possible 
changes  in  the  plates  consequent  upon  its  expansion.  Moreover,  there  is 
an  increased  accuracy,  due  to  the  plaster  being  carried  with  certainty  into 
all  parts.  After  the  plaster  cast  has  been  poured,  the  tray  is  heated  until 
the  shellac  is  softened,  when  the  tray  is  removed  and  the  model  separated 
from  the  impression. 

Selecting  Material  for  Impressions. — Plaster  of  Paris  is  justly  re- 
garded as  the  impression  material  par  excellence.  It  is  extremely 
exceptional  in  the  making  of  an  artificial  denture  that  its  construction  is 
not  preferable  upon  a  basis  of  an  exact  reproduction  of  the  mouth  in  a 
plaster  model.  Plaster  is  the  only  impression  material  which  possesses 
the  properties  which  give  assurance  of  accuracy.  It  is  inserted  without 
the  exertion  of  any  force  which  could  cause  the  displacement  of  movable 
parts,  may  be  insinuated  into  minute  spaces  or  irregularities,  and  after 
setting  its  form  is  unalterable.  The  practised  operator  secures  with  this 
material  impressions  of  any  jaw,  no  matter  what  the  anatomical  pecu- 
liarities may  be.  Impressions  may  be  taken  with  it  of  partial  cases  in 
which  no  two  of  the  remaining  teeth  are  parallel^  (Fig-  327). 

A  general  rule  more  applicable  than  any  other  is  that  "just  in  the 
degree  that  an  impression  is  difficult  to  take,  owing  to  irregularities  of 
form  or  in  the  positions  of  the  teeth,  it  is  imperative  that  it  should  be 
taken  in  plaster."  The  exceptions  to  this  rule  are  so  rare  as  to  scarcely 
require  mention. 

^  See  Cosmos,  Nov.,  1895,  "Old  Dentures." 


IMPRESSION  TRAYS. 


285 


Of  the  several  materials  made  plastic  by  heat,  modelling  compound 
is  usually  regarded  as  having  the  widest  field  of  usefulness.  When  soft 
it  is  sufficiently  plastic  to  receive  imprints  of  fine  lines,  and  yet  it  in- 
evitably displaces  to  a  greater  or  less  degree  the  soft  tissues  against 
which  it  is  pressed.     If  the  natural  teeth  are  in  irregular  positions, 


Fig.  327. 


portions  of  an  impression  are  bent  from  their  true  form  when  the 
impression  is  withdrawn  from  the  mouth.  The  material  being  in  some 
degree  elastic,  this  deformity  tends  to  partially  correct  itself.  It  may 
be  mentioned  that  the  most  common  use  of  this  material  is  for  securing 
impressions  from  which  to  form  orthodontic  appliances. 

Pure  beeswax  becomes  softer  than  modelling  compound  and  at  a  lower 
temperature.  When  soft  it  is  inelastic  :  although  receiving  the  imprints 
of  fine  lines,  it  exhibits  no  tendency  to  adjust  itself  to  undercuts,  as  does 
the  compound.  Additions  of  paraffin  or  gutta-percha  to  a  basis  of  wax 
render  it  firmer.  All  preparations  of  wax  are  distorted  permanently,  to 
some  degree,  in  being  withdrawn  from  undercuts. 

Gutta-percha,  a  substance  once  employed  to  some  extent,  has  fallen 
into  general  disuse  as  an  impression  material,  being  replaced  by  modelling 
compound,  the  latter  possessing  more  virtues  and  fewer  disadvantages 
than  gutta-percha.  The  last-mentioned  material  requires  a  compara- 
tively great  amount  of  heat  to  soften  it :  during  the  operation  of  im- 
pression-taking it  is  driven  into  irregular  spaces,  from  which  it  is  diffi- 
cult to  withdraw  it  when  the  material  is  cold. 

Impressions  in  Heat-softened  Materials. — Impressions  in  any  of  these 
materials  are  taken  after  one  common  principle  :  A  properly  adapted 
tray  is  selected  or  when  necessary  is  fitted  :  the  material  itself  is  placed 
in  lukewarm  water,  the  temperature  being  raised  gradually  until  the 
mass  is  of  uniform  softness.  The  tray  is  heated  sufficiently  to  cause  the 
material  to  adhere  to  it,  when  the  impression  material  is  moulded  in  the 
tray  until  of  almost  uniforni  thickness,  except  at  its  highest  part,  where 
it  is  left  thickest  to  ensure  perfect  contact  with  the  height  of  the  vault. 

The  patient  is  seated  in  a  dental  chair  placed  at  its  lowest  position,  the 
operator  standing  behind.    The  tray  is  held  in  the  right  hand,  two  fingers 


286  TAKING  IMPBESSIONS  OF  THE  MOUTH. 

under  its  body,  the  thumb  on  the  handle.  The  right  side  of  the  impres- 
sion tray  is  to  have  its  middle  engage  and  draw  away  the  lips  at  their 
angle ;  the  fingers  of  the  left  hand  draw  away  the  left  angle  of  the  lip 
when  the  handle  of  the  tray  is  swung  into  the  median  line ;  by  a  steady 
movement  the  impression  material  is  now  pressed  into  position  :  the 
fingers  of  the  left  hand  are  swept  around  the  alveolar  wall,  so  that  the 
cheek  shall  not  interfere  with  the  perfect  placement  of  the  impression 
tray,  which  is  now  firmly  held  in  place  by  two  fingers  pressed  against  the 
bottom  of  the  sides  of  the  tray.  The  patient  is  directed  to  contract  the 
cheeks  and  lip  against  the  impression  material.  When  the  latter  is  cold 
it  is  to  be  withdrawn,  the  fingers  of  the  right  hand  holding  the  tray  as 
during  its  introduction,  the  fingers  of  the  left  hand  lifting  the  cheeks  and 
lips  away.  The  impression  is  plunged  immediately  into  cold  water  to 
chill  and  fix  it. 

In  taking  the  impressions  of  lower  cases  the  operator  usually  stands 
in  front  of  the  patient.  The  same  directions  apply  in  the  taking  of 
these  as  in  upper  impressions.  As  soon  as  the  material  is  pressed  into 
position  the  patient  is  directed  to  protrude  the  tongue,  so  that  the  adja- 
cent portion  of  impression  will  be  pressed  into  position. 

Plaster  Impressions. — For  the  taking  of  any  plaster  impressions  a 
properly  adapted  tray  is  essential.  It  is  necessary  that  its  outlines 
should  be  larger  and  greater  in  depth  than  the  future  denture.  Between 
the  tray  and  the  arch  and  vault  should  be  a  space  of  about  one-quarter  of 
an  inch — rarely  less,  except  at  the  posterior  border  of  upper  impressions, 
as  very  thin  layers  of  plaster  are  liable  to  fracture  in  pieces  too  small  for 
accurate  replacement.  With  a  greater  distance  between  the  tray  and 
the  parts  of  which  an  impression  is  to  be  taken  there  is  danger  that 
the  plaster  will  not  be  properly  carried  into  position. 

For  full  upper  cases  trays  having  a  raised  heel  (Fig.  316)  are  em- 
ployed, or  a  layer  of  wax  is  built  across  the  heel  so  that  the  plaster 
cannot  escape  posteriorly. 

Each  fresh  purchase  of  plaster  should  be  tested,  so  that  the  length 
of  time  required  for  setting  may  be  determined.  Impression  plaster 
should  set  more  rapidly  than  that  used  for  casts,  but  should  permit 
thorough  mixing  and  placing  before  it  begins  to  harden. 

Arranging  Patient  to  Take  Impression. — The  patient  should  be  seated, 
and  instructions  given  as  to  position  and  the  reasons  therefor;  the  patient 
inclining  the  body  slightly  forward,  and  in  readiness  when  the  plaster  is 
introduced  to  allow  the  head  to  be  thrown  still  more  forward,  the  object 
being  to  determine  any  excess  of  plaster  to  the  front  of  the  mouth  and 
prevent  it  from  falling  into  the  fauces.  Too  many  directions  and  an 
ostentatious  preparation  will,  however,  cause  failure  with  timid  patients, 
by  inducing  undue  nervous  irritability  from  a  magnified  fear  of  the  ope- 
ration. 

When  about  to  take  a  plaster  impression  a  towel  or  large  napkin 
should  be  spread  in  the  front  of  the  patient's  dress  to  receive  any  excess 
of  plaster  which  may  be  dislodged. 

The  patient  may  be  directed  to  dry  the  mouth  with  a  soft  napkin  if 
there  is  an  excess  of  saliva,  but  this  is  rarely  if  ever  necessary  in  taking 
impressions  of  the  upper  jaw,  and  some  mouths  are  naturally  so  dry  that 
the  difficulty  is  rather  to  prevent  the  plaster  from  adhering  too  firmly  to 


IMPRESSION  TEAYS. 


287 


the  tissues.  In  such  cases  it  is  not  well  to  absorb  what  little  moisture 
there  may  be.  Some  operators  always  direct  the  mouth  to  be  rinsed  with 
warm  water,  which,  it  is  claimed,  by  removing  the  mucus  facilitates  a 
more  even  flow  of  the  plaster,  diminishes  its  liability  to  an  undue  adhe- 
rence to  the  membranes,  and  produces  a  smoother  and  more  delicate  im- 
pression. Some  always  brush  the  parts  over  with  glycerol  if  the  mucous 
membrane  appears  abnormally  dry. 

Before  introducing  the  tray  some  operators  instruct  the  patient  to 
breathe  through  the  nostrils,  considering  that  the  liability  of  fragments 
of  plaster  being  drawn  into  the  pharynx  is  much  increased  when  the 
patient  breathes  through  the  mouth. 

The  late  Dr.  Joseph  Richardson  took,  however,  an  opposite  view, 
arguing  that  in  the  act  of  breathing  through  the  nose  the  velum  palati 
is  depressed  to  cut  off  the  passage  of  air  through  the  mouth,  and  is  thus 
brought  more  immediately  in  contact  with  any  portion  of  plaster  that 
may  be  protruding  from  the  heel  of  the  tray  ;  that  the  stimulus  of  contact 
produces  involuntary  contraction,  and  that  thus  fragments  of  hard  plaster 
may  be  drawn  back  into  the  fauces,  producing  the  very  evils  which  nose- 
breathing  is  thought  to  avoid ;  and  that  if  patients  are  instructed  at  all 
in  this  respect,  they  should  be  advised  to  breathe  through  the  mouth.  ^ 

About  a  gill  of  water  is  placed  in  a  rubber  plaster-bowl  (Figs.  328- 
330)  and  a  pinch  of  salt  added.     These  bowls  of  soft  vulcanized  rub- 


Fio.  328. 


Fig.  330. 


Fig.  329. 


Rubber  bowls  for  mixing  plaster. 

ber  cannot  be  broken ;  their  sides  can  be  pressed  together  to  form  a 
lip  or  spout  for  pouring  thin-mixed  plaster ;  and  any  unused  plaster  of 
the  mixing  which  sets  in  them  can  be  thoroughly  crushed  and  readily 
removed  by  squeezing  the  sides  of  the  bowls  together.  Their  superi- 
ority has  made  for  them  a  place  in  almost  every  dental  laboratory. 
Plaster  is  slowly  sifted  into  the  water  until  it  is  at  the  surface  of  the 
^  J.  W.  White :  Taking  Impression  of  Mouth. 


288 


TAKING   IMPRESSIONS  OF  THE  MOUTH. 


Fig.  331. 


latter,  when  it  is  stirred  with  the  spatula  until  a  thin  paste  is  made.  A 
quantity  of  the  batter  is  carried  into  the  tray  and  distributed  by  means 
of  the  spatula  until  it  is  something  more  than  a  quarter 
of  an  inch  in  depth. 

The  tray  is  carried  into  the  mouth  as  described :  its 
posterior  edge  is  first  brought  into  position,  and  then  by  a 
gradual  elevation  of  the  handle  of  the  tray  the  plaster  is 
carried  into  all  depressions ;  the  cheeks  and  lips,  lifted 
away,  are  allowed  to  fall  back  against  the  plaster  which  has 
pressed  over  the  edges  of  the  tray,  carrying  it  into  close 
contact  with  the  alveolar  walls.  The  impression  is  now 
held  immovably  in  position  until  by  test  of  the  plaster  re- 
maining in  the  bowl  it  is  seen  that  the  impression  is  hard. 
The  lips  and  cheeks  are  lifted  from  the  impression ;  the 
handle  of  the  tray  is  elevated  to  detach  the  heel  of  the 
impression,  which  is  now  withdrawn. 

Should  the  case  present  an  unusual  depth  of  palatal 
vault,  air  may  be  enclosed  between  the  soft  plaster  and  the 
mucous  membrane  and  produce  flaws  in  the  impression. 
It  is  advisable  in  such  cases  to  fill  the  tray  with  plaster ; 
then  a  portion  of  the  batter  is  taken  on  the  end  of  the 
spatula-blade  and  carried  into  the  height  of  the  vault, 
smearing  the  plaster  into  the  deepest  recesses  :  the  plaster 
in  the  tray  is  immediately  carried  into  position,  joining  the 
plaster  of  the  tray  with  that  in  the  vault. 

It  is  occasionally  found  that  patients  have  what  are 
called  "  irritable  throats,"  the  presence  of  any  substance  in 
contact  with  the  soft  palate  causing  any  degree  of  protest 
from  a  slight  gagging  to  marked  retching  or  even  vomiting. 
It  is  necessary,  in  such  cases,  to  temporarily  benumb  the 
parts  to  enable  the  operator  to  secure  an  impression.  The 
usual  means  of  securing  this  end  is  through  the  employ- 
ment of  a  gargle  of  camphor-water  (not  spirits  of  cam- 
phor). This  suffices  in  many  cases  :  the  more  irritable 
ones  are  directed  to  employ  a  gargle  of  potassium  bro- 
mide, gr.  XX,  water  an  ounce.^ 

Should  these  means  not  suffice,  the  patient  is  given  a 
gargle  of  glycerin  and  water ;  after  a  thorough  lavage 
with  this  the  soft  palate  and  pharynx  are  sprayed  with  a 
1  per  cent,  solution  of  cocaine  hydrochlorate  in  an  atomizer. 
In  five  minutes  an  impression  may  be  taken  without  fur- 
ther difficulty. 

In  taking  lower  impressions  the  batter  is  made  slightly 
thicker  than  for  upper  cases.  The  tray  is  carried  into 
position,  and  before  pressing  it  home  a  tremulous  move- 
ment is  made  to  introduce  the  plaster  into  undercuts ; 
then  it  is  pressed  into  position  and  firmly  held  upon  both 
sides.  The  patient  is  directed  to  protrude  the  tongue  to 
carry  the  plaster  well  against  the  alveolar  wall  anteriorly.  Lower 
impressions   are    permitted    to    remain    longer    in    position   than    those 

^  Oral  Surgery,  Garretson. 


Spatula  or 
palette-knife. 


IMPRESSION  TRAYS  289 

for  upper  dentures,  for,  being  bathed  in  saliva,  they  set  more 
slowly. 

In  taking  plaster  impressions  tlie  handle  of  the  impression  tray  should 
always  be  in  the  median  line,  and  the  body  of  the  impression  should  be 
held  immovably  in  position  supported  upon  both  sides. 

Any  pieces  of  impression  which  may  break  from  it  during  its  re- 
moval are  carefully  preserved  and  fitted  into  their  proper  positions.  The 
plaster  when  fully  set  breaks  with  a  clearly  defined  fracture  line,  furnish- 
ing a   guide  for  the  accurate  replacement  of  fragments  or  sections. 

Cases  are  occasionally  met  with  where  the  patient  complains  of  the 
instability  of  a  denture  now  worn  :  an  examination  shows  an  apparently 
accurate  adaptation  of  the  plate  to  the  vault  and  the  teeth  in  proper  oc- 
clusion. Removing  the  artificial  denture  and  passing  the  finger  over  the 
area  of  the  vault  and  arch,  it  will  be  observed  that  the  tissues  do  not 
offer  uniform  resistance  to  pressure  ;  certain  areas  are  hard,  others  soft  or 
spongy,  so  that  a  plate  closely  adapted  to  the  mouth  at  rest  would  exert 
uneven  pressure  upon  its  bed.  Many  operators  prefer  for  such  cases 
beeswax  or  modelling  compound  as  an  impression  material,  which  by 
pressing  away  the  soft  parts  should  cause  a  plate  made  upon  such  models 
to  have  a  uniform  bearing.  Unfortunately,  this  one  feature  of  these 
materials  rarely  compensates  for  their  lack  of  accurate  adaptation  to  the 
parts  and  the  danger  of  change  of  form  in  them. 

The  offices  and  advantages  of  wax  or  compound  and  plaster  are  com- 
bined in  the  following  method  :  An  impression  is  taken  either  in  wax 
or  compound ;  then  by  testing  the  density  of  the  tissues  the  hard  areas 
are  determined  and  the  impression  is  carved  away  at  these  parts.  The 
prepared  impression  then  serves  as  an  impression  tray  in  which  an  im- 
pression in  plaster  is  taken.  The  greatest  pressure  is  evidently  exerted 
by  those  portions  of  the  improvised  tray  which  have  not  been  cut  away, 
those  beneath  the  soft  areas. 

Dr.  B.  H.  Catching^  describes  a  method  of  quickly  making  special 
impression  trays,  for  which  the  operator's  ingenuity  Avill  devise  many  ap- 
plications :  A  piece  of  base-plate  wax  is  moulded  to  fit  approximately 
the  parts  to  be  enclosed  by  the  tray.  This  when  removed  from  the 
mouth — or  model  if  it  be  formed  upon  a  model — is  chilled  and  a  wax 
handle  formed.  A  plaster  matrix  is  made  of  the  tray  in  an  exterior  and 
interior  section.  The  walls  of  the  matrix  should  be  thin.  After 
separating  the  halves  of  the  matrix  the  wax  tray  is  removed,  the 
matrix  bound  together,  and  the  space  formerly  occupied  by  the  wax  is 
filled  with  molten  fusible  metal.  If  the  tray  is  to  be  made  of  an  alloy 
having  a  higher  melting-point,  the  matrix  is  to  be  formed  in  sand  and 
plaster  mixture  and  well  dried  before  the  metal  is  poured. 

Impressions  for  Partial  Dentures. — The  necessity  for  a  properly 
adapted  tray  is  redoubled  in  the  taking  of  impressions  for  partial  den- 
tures. One  of  the  square-edged  trays  illustrated  is  selected  whose  arch  is 
a  quarter  of  an  inch  larger  than  that  of  the  teeth.  Closely  fitting  trays 
frequently  cause  the  plaster  about  the  natural  teeth  to  break  into  such 
small  fragments  that  accurate  replacement  of  them  is  impracticable. 
Across  the  heel  of  the  cup  a  dam  of  wax  is  built,  so  that  the  plaster  will 
be  well  enclosed  and  none  or  but  little  of  it  shall  escape  posteriorly.    Any 

^  Comp.  of  Pract.  Dent.,  1895. 
19 


290 


TAKING   IMPEESSIONS   OF  THE  MOUTH. 


further  lack  of  adaptation  is  to  be  corrected  by  building  wax  about  the 
borders  of  the  tray  or  cutting  away  from  the  latter  parts  which  may 
interfere  with  its  proper  placement.  The  tray  is  filled  with  plaster — an 
examination  of  the  comparative  sizes  of  the  tray  and  mouth  will  indicate 
the  quantity  of  plaster  required — and  it  is  carried  into  position  in  the  man- 
ner previously  described.  When  the  plaster  and  tray  are  in  position  they 
should  be  held  by  the  fingers  of  both  hands  to  ensure  against  rocking. 
When  the  plaster  has  set  the  cheeks  and  lip  are  raised  from  the  impres- 
sion, and  the  latter  is  loosened  by  depressing  its  heel. 

It  is  usual,  and  in  many  cases  inevitable,  that  there  is  a  greater  or 
less  amount  of  fracture  of  partial  impressions.  The  body  of  the  impres- 
sion, that  in  the  tray,  is  set  aside,  and  all  broken  pieces  are  lifted  away 
with  a  pair  of  tweezers  and  ranged  around  the  tray.  An  examination 
is  made  of  the  spaces  about  and  between  the  teeth  and  any  fragments 
found  are  detached  and  preserved.  As  soon  as  the  impression  is  dry 
enough,  in  about  fifteen  minutes,  each  fractured  surface  is  brushed  free 
of  any  adherent  particles  (the  brush  should  be  very  soft).  The  greater 
masses  are  now  adjusted  to  one  another,  and  the  shapes  of  the  spaces 
between  parts  of  them  noted  ;  the  pieces  which  fit  such  spaces  are  selected 
from  the  smaller  fragments  and  set  in  position  until  the  surfaces  of  the 
impression  are  complete.  The  pieces  should  be  so  adjusted  to  one  another 
as  to  make  the  lines  of  junction  almost  indistinguishable. 

Fig.  332. 


Weirich's  new  flexible-rim  impression  trays. 


Melted  adhesive  wax  is  applied  to  each  joint  upon  the  exterior  of 
the  impression  to  hold  the  pieces  in  their  positions.  Small  pieces  which 
it  is  impossible  to  thus  attach  without  applying  wax  to  the  inner  surface 


IMPRESSION  TRAYS.  291 

of  the  impression  may  be  made  to  adhere  by  treating  the  surfaces  to  be 
joined  with  thin  mucilage  (Fig.  332). 

The  impression  tray  of  Dr.  Weirich  is  designed  for  the  taking  of  im- 
pressions of  the  forms  which  suifer  fracture  of  their  outer  walls  in  with- 
drawing them  from  the  mouth.  The  soft  plaster  exudes  through  the 
perforations  of  the  flexible  rubber  rims  when  the  tray  is  carried  into 
position  in  the  mouth,  \yhen  hardened  the  plaster  is  thus  held  firmly 
against  the  flexible  wall.  As  the  impression  is  withdrawn  from  its  posi- 
tion it  fractures  above  the  sites  of  undercuts  :  the  flexible  rim  yields, 
and  yet  holds  the  broken  sections  firmly,  and  when  removed  from  the 
mouth  the  elastic  rim  carries  these  sections  back  exactly  into  position. 

The  operation  of  taking  partial  lower  impressions  is  essentially  the 
same.  The  tray  is  to  be  one-fourth  of  an  inch  larger  than  the  arch  at 
all  points,  and  the  edges  of  the  tray  are  to  extend  beyond  the  plate 
outlines.  The  most  common  classes  of  cases,  those  in  which  the  anterior 
natural  teeth  are  in  situ,  are  taken  in  the  variety  of  tray  made  for  them. 
(See  Fig.  321.) 

Where  the  natural  teeth  are  present  at  irregular  intervals,  trays 
having  square  edges,  such  as  figured,  are  employed  ;  if  the  teeth  are  very 
long,  trays  such  as  are  shown  in  Fig.  334  are  applicable. 

It  is  usual  that  these  impressions  suffer  extensive  fracture  in  their 
remoyal. 

A  tray  filled  with  plaster  is  inserted,  and  before  pressing  it  fully  into 
position  is  jarred,  so  that  the  plaster  will  be  brought  into  perfect  contact 
with  all  portions  of  the  dental  arch.  It  is  then  pressed  into  place,  and 
held  until  it  has  set  hard.  Cases  in  which  the  natural  teeth  are  in  an 
unbroken  line  usually  fracture  less  than  those  in  which  the  teeth  are 
scattered.  The  pieces,  large  and  small,  are  collected  and  each  is  accu- 
rately fastened  into  position. 

Should  the  spaces  between  the  teeth  present  marked  undercuts,  or 
should  any  of  the  natural  teeth  be  loose,  it  is  advisable  to  remove  the 
impression  in  sections  in  such  a  manner  as  to  produce  no  strain  upon 
loose  teeth  and  to  preserve  the  shapes  of  undercuts.  This  applies 
equally  to  partial  upper  cases  in  which  similar  conditions  are  present. 
A  square-edged  cup  is  selected  and  its  inner  surface  oiled.  The  posi- 
tions of  the  natural  teeth  are  noted — which  of  them  are  loose  and  inclined. 
The  tray  and  plaster  are  carried  into  position  as  before,  and  when  the 
impression  is  hard  the  tray  is  withdrawn,  leaving  the  impression  in  the 
mouth.  With  a  sharp  knife-blade  groove  the  impression  along  a  line 
which  will  pass  through  the  middle  of  the  articulating  face  of  each 
tooth.  When  the  groove  extends  to  the  crowns  of  the  teeth,  transverse 
cuts  are  made  from  the  outer  wall  of  the  impression  into  the  buccal 
or  labial  surfaces  of  the  teeth  :  these  grooves  mark  the  impression  into 
inner  and  outer  sections  and  into  two  or  more  sections  anteriorly.  The 
tip  of  a  finger  is  introduced  beneath  the  edge  of  a  posterior  section,  and 
it  is  detached  ;  the  remaining  outer  sections  are  removed  in  the  same 
manner.  A  finger  introduced  between  the  natural  teeth  exerts  pressure 
upon  the  inner  section  of  the  impression,  and  it  is  pushed  upon  until 
loosened  and  detached.  The  writer  has  never  met  with  a  case,  no  matter 
how  irregular,  of  which  a  plaster  impression  could  not  be  secured  by  a 
careful  following  of  this  method. 


292 


TAKING  IMPRESSIONS  OF  THE  MOUTH. 


The  several  pieces  are  adjusted  to  one  anotlier,  and  cemented  together 
and  to  the  tray. 

It  has  been  recommended  in  taking  impressions  for  this  class  of  cases 
that  a  wax  impression  be  first  taken,  which  is  then  carved  out  to  serve 
as  a  tray  in  securing  an  impression  in  plaster.  This  method  is  applica- 
ble when  there  is  but  slight  danger  of  fracture  of  the  plaster  in  remov- 
ing the  impressions  from  the  mouth,  but  when  the  irregularity  of  the 
parts  embraced  by  the  impression  is  marked  enough  to  cause  fracturing 
of  the  impression,  many  of  the  fragments  of  the  latter  will  be  found 
too  small  and  too  thin  for  accurate  replacement.  Moreover,  the  heat 
engendered  by  the  setting  of  the  plaster  softens  the  wax  matrix  and  fre- 
quently renders  the  accurate  replacement  of  fragments  impossible.  For 
this  reason  it  is  better  to  secure  the  primary  impression  in  modelling 
compound,  cutting  it  away  until  it  is  of  the  proper  size  and  form. 

In  cases  which  have  remaining  one  or  two  unusually  long  natural 
teeth  it  is  advisable  to  cut  large  openings  in  the  tray  which  shall  permit 
the  ready  placing  of  the  tray  in  position  (Fig.  333,  A  ;  334,  J.).  Without 
these  apertures  a  tray  rides  on  the  natural  teeth,  so  that  it  is  difficult  to 
prevent  movement  of  the  impression  while  it  is  setting.  The  setting  of  a 
thick  mass  of  plaster  about  isolated  teeth,  which  are  frequently  at  an  acute 

Fig.  333. 


angle  with  the  plane  of  the  mouth,  and  which  are  broader  upon  their 
masticating  surfaces  than  at  their  necks,  renders  it  most  difficult  to  remove 
the  impression.    About  the  openings  cylinders  at  least  twice  as  wide  as  the 


IMPRESSION  TRAYS. 


293 


teeth  are  attached  (Fig.  333,  B  ;  Fig.  334,  B) :  these  may  be  made  of  the 
heavy  pattern  tin  of  the  laboratory  or  of  sheet  wax  :  wax  is  melted  about 
their  bases  to  hold  them  to  the  tray.  The  tray,  filled  with  plaster,  is 
carried  into  position.    The  body  of  the  tray  should  be  well  adapted  to  the 


Fig.  334. 


alveolar  arch,  so  that  the  body  of  the  impression  is  quite  thin.  When  the 
plaster  is  hard  the  cylinders  are  stripped  from  the  plaster.  A  groove  is 
made  along  the  length  of  the  plaster  projection  until  the  knife-blade  is  felt 
to  touch  the  enclosed  tooth.  Introducing  a  broad  dull  blade  in  the  groove, 
the  cylinders  are  split  in  two  sections,  making  sharp  fracture  surfaces.  The 
tray  and  body  of  the  impression  are  now  withdrawn,  and  the  plastic  cylin- 
ders adjusted  and  cemented  to  it.  It  is  occasionally  necessary,  as  has  been 
stated,  to  alter  the  original  forms  of  trays  to  make  them  conform  to 
irregularities  of  the  parts  embraced  by  the  impression.  While  slight 
alterations  by  cutting,  filing,  or  bending  may  serve  to  adapt  the  tray  in 
many  cases,  there  are  others  in  which  it  may  be  necessary  to  so  trim  a 
tray  that  it  is  out  of  all  resemblance  to  its  original  form.  At  the  site  or 
sites  of  a  column  or  columns  of  natural  teeth  it  may  be  necessary  to 
remove  entirely  those  portions  of  the  tray  which  interfere  with  the  pas- 
sage of  the  tray  to  within  one-eighth  of  an  inch  of  the  vault.  Instances 
and  illustrations  of  this  necessity  and  the  modus  operandi  of  making  the 
changes  are  appended.  Fig.  335  shows  the  tray  in  process  of  being  cut 
by  means  of  plate-nippers,  the  most  expeditious  means  of  making  the 


294 


TAKING   IMPRESSIONS  OF  THE  MOUTH. 


changes  without  that  distortion  of  the  general  edge  outline  of  the  tray 
which  accompanies  trimming  by  shears.  Fig.  336  illustrates  a  tray  for  a 
partial  lower  case  cut  out  for  the  passage  of  the  anterior  teeth,  the  lingual 
wall  of  the  tray  being  divided  to  accommodate  an  unusual  confirmation 
of  the  lingual  aspect  of  the  alveolar  wall.  Fig.  337  shows  a  tray  pre- 
pared for  taking  an  impression  for  a  partial  upper  case. 


Fig.  335. 


Fig.  336. 


Fig.  337. 


The  trays,  altered  so  that  they  will  pass  readily  into  position,  have 
softened    sheet  wax    moulded    about   the    openings,  forming  chambers 

slightly  deeper  than  the  lengths  of  the 
teeth  and  about  twice  as  broad.  Their 
edges  are  cemented  to  the  tray  about 
one-eighth  of  an  inch  beyond  the  bor- 
ders of  the  openings  in  the  trays,  so 
that  the  plaster  of  the  impression  will 
be  caught  by  the  under  surface  of  the 
tray  at  these  points  and  serve  to  with- 
draw the  impression  in  the  tray. 

Cases  are  occasionally  seen  in  which 
the  plaster  exhibits  an  undesirable 
tendency  to  cling  to  the  surfaces  of  the 
teeth.  To  overcome  this  it  is  the  usual 
practice  to  coat  each  natural  tooth  with 
olive  oil  before  taking  the  impression. 
A  ball  of  cotton  is  dipped  in  the  oil, 
and  then  passed  over  the  surfaces  of 
the  teeth.  As  in  these  cases  the  plaster  tends  to  adhere  to  the  mucous 
membrane  also,  the  oiled  cotton  is  to  be  passed  over  all  portions  of  the 
mouth  to  be  embraced  by  the  impression.  Dr.  L.  C.  Ingersoll^  advises 
mixing  in  the  plaster  batter  about  one-third  of  its  volume  of  pulverized 
pumice. 

In  rare  instances  the  natural  teeth  may  converge  toward  one  another,  so 

'  J.  W.  White :   Taking  Impression  of  the  Mouth. 


IMPRESSION  TRAYS. 


295 


that  their  walls,  together  with  the  palatal  vault,  form  more  than  a  hemi- 
sphere seen  in  section  or  semicircle  (Fig.  338).  It  is  evident  that  in  snch  a 
case  it  would  be  impossible  to 

withdraw  en  masse  the  body  Fig.  338. 

of  an  enclosed  impression 
without  displacement  of  these 
teeth.  It  is  necessary  that 
this  portion  of  the  impression 
shall  be  removed  in  halves. 
To  render  this  division  as 
easy  as  it  should  be,  a  wedge- 
shaped  piece  of  modelling 
compound  is  placed  along  the 
median  line  of  the  tray,  and 
deep  enough  for  its  sharp  edge  to  be  in  contact  with  the  palatal  vault. 
The  impression  tray  is  heated  and  roughened  along  its  line  of  attach- 
ment to  secure  it  firmly  to  the  compound,  which  is  chilled  and  the  .sides 
of  the  wedge  made  smooth  and  flat,  then  oiled,  as  is  also  the  interior  of 
the  tray.  The  tray  is  filled  with  plaster  and  placed  in  the  mouth  :  when 
hard  the  tray  is  removed  and  the  outer  portion  of  the  impression  detached. 
If  the  wedge  of  compound  has  not  come  away  with  the  impression  tray,  a 
hook  instrument  is  inserted  in  its  posterior  wall,  and  by  this  means  it  is 
detached.  The  right  and  left  segments  of  the  impression  may  now  be 
removed  without  difficulty. 

Occasionally  it  may  be  required  of  the  dental  operator  to  take  an 
impression  of  an  arch  in  which  one,  or  it  may  be  several,  of  the  teeth 
are  loose,  and  it  is  designed  to  retain  them  until  a  fixture  is  ready 
to  be  inserted,  so  that  the  patient  may  be  spared  the  annoyance,  humili- 
ating to  morbidly  sensitive  persons,  of  exhibiting  vacant  spaces  in  the 
dental  arch.  The  greater  number  of  these  cases  are  those  suffering  from 
some  phase  of  pyorrhoea  alveolaris.  The  teeth  are  recognized  by  the 
operator  as  being  past  hope  of  retention,  and  the  patient  protests  against 
their  forcible  extraction,  preferring  to  await  the  inevitable  exfoliation. 
In  such  cases  a  tray  is  adapted  :  its  inner  surface  is  oiled,  and  the  tray  is 
withdrawn  from  the  impression,  which  is  then  removed  in  sections  to 
avoid  stress  upon  the  loose  teeth. 

Unusual  care  must  be  exercised  in  these  cases,  as  the  danger  of 
extracting  the  loose  teeth  in  withdrawing  the  impression  is  not  remote. 
Particular  care  must  be  observed  to  secure  an  accurate  impression  of  the 
gums  and  gingival  margins. 

If  the  case  be  one  for  which  a  new  plate  is  to  be  made,  the  plaster 
teeth  are  cut  from  the  model,  and  the  plaster  cut  away,  representing 
accurately  the  appearance  and  form  of  the  gums  when  the  loose  teeth 
shall  have  been  lost.  This  trimming,  while  following  with  exactitude 
the  gum  outline  which  will  be  left  at  the  site  of  each  lost  tooth,  should 
be  of  sufficient  depth  to  ensure  the  close  adaptation  of  the  future  plate 
to  the  natural  gum. 

In  taking  impressions  for  cases  requiring  palatal  restoration  either  of 
hard  or  soft  palate,  or  of  both,  it  is  required  that  an  accurate  impression 
be  secured  of  all  of  the  edges  of  the  opening  representing  the  anatom- 
ical deficiency.    An  examination  of  the  anatomical  parts  will  exhibit  the 


296  TAKING  IMPRESSIONS   OF  THE  MOUTH. 

palatal  structures  as  a  partition-wall  between  the  nasal  and  oral  cavities  : 
it  is  evident,  therefore,  that  care  must  be  exercised  and  means  adopted 
which  shall  prevent  the  entrance  into  and  the  retention  of  the  impression 
material  in  the  second,  the  nasal  chamber,  an  impression  of  which  for 
present  purposes  is  not  required. 

An  effective  method  for  securing  the  desired  impression  is  that 
devised  by  the  late  Prof.  Geo.  T.  Barker,  and  employed  by  him  almost 
exclusively.  A  piece  of  soft  sponge  is  trimmed  to  approximate  the 
form  of  the  break,  and  make  slightly  larger  than  it ;  the  sponge  is  to  be 
softened  in  warm  water.  The  sponge  is  then  saturated  with  a  batter  of 
impression  plaster,  placed  and  held  carefully  in  position  until  the  plaster 
has  hardened.  The  sponge  is  then  carried  backward  to  separate  it  from 
the  parts  and  permit  its  removal.  Its  under  (the  lingual)  surface  is 
trimmed  smooth,  varnished,  and  oiled,  and  replaced  in  its  position. 
The  case  is  now  one  to  which  the  ordinary  methods  of  impression- 
taking  apply,  except  that  the  extent  of  surface  is  greater.  An  extension 
of  tin  or  of  wax  is  cemented  to  the  heel  of  an  appropriate  impression 
tray,  this  extension  to  be  long  enough  to  carry  the  plaster  to  the  poste- 
rior pharyngeal  wall.  The  tray  is  tilled  with  plaster,  carried  into  posi- 
tion, and  held  until  the  material  has  hardened.  The  impression  is  with- 
drawn, separating  it  from  the  sponge  section,  which  is  next  detached  and 
set  in  its  proper  position  in  the  body  of  the  impression. 

In  taking  impressions  of  cases  of  fractured  maxillse,  for  which  inter- 
dental splints  are  to  be  made,  no  attempt  at  the  full  reduction  of  the  dis- 
placement is  attempted.  Plaster  of  Paris  is  the  impression  material  to  be 
employed,  as  its  proper  manipulation  in  these  cases  is  attended  by  the 
exhibition  of  less  force  than  with  any  other  material.  A  large  impression 
tray  is  selected,  its  surfaces  are  freely  oiled,  a  plaster  batter  is  placed  in  it, 
and  the  tray  is  carried  into  position.  When  the  plaster  has  hardened  the 
oiled  tray  is  detached,  separating  readily.  The  impression  is  next  re- 
moved in  sections,  which  are  adjusted  to  the  tray,  cemented  together, 
varnished,  and  a  plaster  cast  poured.  The  further  steps  of  these  opera- 
tions will  be  described  under  the  head  of  "  Interdental  Splints  "  in  the 
chapter  on  "  Dentures  upon  the  Vulcanized  Caoutchouc  Base."  ^ 

Impressions  into  which  molten  metal  is  to  be  poured  are  taken  in  a 
mixture  of  plaster  and  marble  dust,  pumice,  or  whiting,  the  mixture 
requiring  a  greater  length  of  time  for  setting  than  does  plaster  alone. 
The  impression  is  placed  in  an  oven  and  carefully  and  thoroughly  dried  : 
it  is  now  set  in  a  bed  of  moulding  sand,  which  is  built  up  around  it  to 
any  depth  it  is  desired  to  have  the  metallic  model.  The  metal,  usually 
tin,  to  serve  as  a  base  upon  which  a  vulcanite  plate  is  formed  is  poured 
in  the  impression  and  sand  walls.  Impressions  taken  in  this  mixture 
are  by  some  operators  made  to  serve  as  soldering  investments  for  bridge- 
pieces. 

Models  of  what  are  known  as  the  fusible  alloys  may  be  poured  in 
plaster  impressions  as  soon  as  the  latter  are  removed  from  the  mouth  : 
such  models  are  never  to  be  subjected  to  a  temperature  above  150°  F. 

1  C.  J.  Essig. 


CHAPTER  YII. 

MAKING  OF  MODELS  AND  THEIR  PREPARATION. 

By  H.  H.  Buechaed,  M.  D.,  D.  D.  S. 


Impeessions  of  modelling  compound  receive  no  treatment  prelim- 
inary to  pouring  the  plaster  cast,  except  that  they  are  dipped  in  water 
and  the  surplus  of  the  latter  shaken  out,  leaving  a  moist  surface  over 
which  the  plaster  batter  will  flow  freely.  When  the  cast  is  hard  the 
modelling  compound  separates  readily  from  its  surface  when  the  impres- 
sion is  softened  by  heat.  Wax  impressions  receive  a  coating  of  thin 
sandarac  varnish  prior  to  forming  the  cast ;  then,  if  the  wax  is  not  made 
too  hot,  it  will  separate  from  the  plaster  without  adhesion  to  its  surface. 
Without  the  interposition  of  the  layer  of  varnish  the  wax  exhibits  a 
tendency  to  cling  to  the  cast. 

All  of  the  pieces  broken  from  a  plaster  impression  in  its  removal 
from  the  mouth  are  to  be  carefully  preserved  and  fitted  to  their  proper 
positions.  This  detail  frequently  requires  the  exercise  of  much  patience, 
but  when  it  is  considered  that  any  defects  existing  in  the  impression  are 
reproduced  in  the  model,  and  that  the  success  of  a  finished  piece  depends 
primarily  upon  the  accuracy  of  the  model,  it  becomes  evident  that  time 
spent  in  carefully  putting  together  a  broken  impression  is  ultimately 
time  saved. 

Each  piece  is  fastened  into  position  and  the  impression  attached  to  the 
tray  by  means  of  adhesive  wax.  At  the  completion  of  this  operation  it 
should  be  noted  that  the  impression  is  in  accurate  contact  with  the  cup, 
that  the  lines  of  fracture  are  but  hair  lines,  and  that  all  edges  are  closely 
adapted  to  those  of  the  tray.  Any  minute  imperfections  may  be  rem- 
edied by  placing  small  pieces  of  softened  wax  in  them,  and  by  means  of 
a  spatula  making  it  flush  with  the  surface  of  the  impression. 

Separating  Media. — It  is  necessary  to  coat  the  surface  of  the  impres- 
sion with  some  medium  which  shall  prevent  the  adhesion  of  the  plaster 
of  the  cast  to  the  impression,  and  yet  be  of  such  tenuity  as  not  to  oblit- 
■erate  any  of  the  fine  lines  of  the  latter. 

A  wash  of  soapsuds  is  employed  in  some  laboratories  as  a  separating 
medium.  An  ounce  of  Castile  soap  is  placed  in  a  pint  of  water,  which  is 
then  heated  until  the  soap  dissolves.  This  solution  is  painted  over  the 
surface  of  the  impression  while  the  latter  is  still  damp,  and  as  soon  as 
the  impression  is  glazed  the  cast  may  be  poured. 

Thin  solutions  of  collodion  painted  over  the  surface  of  the  impres- 
sion will  glaze  its  surface  and  prevent  the  adhesion  of  soft  plaster. 

The  method  most  commonly  and  acceptably  employed  is  by  double 

297 


298  MAKING    OF  MODELS  AND   THEIR   PREPARATION 

varnishing  the  impression.  After  the  latter  has  set  for  about  half  an 
hour,  long  enough  for  it  to  harden  perfectly  and  yet  not  dry  out,  a  large 
camel's-hair  pencil  is  dipped  in  shellac  varnish  and  a  thin  coating 
applied  to  all  the  surfaces  of  the  impression :  this  speedily  soaks  into 
the  substance  of  the  plaster.  Every  part  of  the  impression  is  to  be 
colored  a  light  brown.  This  coating  should  not  be  thick  enough  to  glaze 
the  surfaf^e,  as  it  is  the  coloring,  not  the  separating  medium  proper. 
When  the  shellac  is  dry  a  uniform  coating  of  sandarac  varnish  is 
applied  :  this  should  give  a  glaze  to  the  surface  of  the  plaster,  and  yet 
should  not  be  thick  enough  to  obliterate  any  fine  lines.  It  is  the  prac- 
tice in  some  laboratories  to  apply  a  third  coat,  one  of  oil.  This  is  quite 
unnecessary ;  moreover,  should  there  be  the  slightest  excess  of  the  oil 
that  portion  of  the  plaster  in  contact  with  it  is  made  soft,  and  this  may 
injure  the  model. 

Several  varnishes  have  been  suggested  one  coat  of  which  shall  serve 
the  double  office  of  coloring  the  impression  to  some  depth  and  glazing 
its  surface.  These  varnishes  must  not  be  thick  enough  to  obliterate  any 
of  the  fine  lines  of  the  impression. 

Should  the  case  be  one  in  which  there  are  isolated,  long,  or  irregular 
teeth  whose  plaster  forms  are  liable  to  fracture  in  separating  the  model 
from  the  impression,  or  which  it  may  be  desirable  to  subsequently  remove 
from  the  model,  long  toilet  pins  are  thrust  into  each  tooth  impression  : 
when  more  than  one  tooth  requires  support,  see  that  the  pins  are  as 
nearly  parallel  as  practicable. 

With  lower  impressions  it  is  a  general  practice  to  cut  a  piece  of  sheet 
wax  to  fit  between  the  inferior  edges  of  the  impression,  so  that  a  flat 
surface  is  made  representing  the  floor  of  the  mouth. 

The  prepared  impressions  now  represent  matrices  in  which  a  model 
is  to  be  cast  which  shall  be  an  exact  reproduction  of  the  jaw  in  plaster. 
This  cast  is  to  be  so  made  that  it  exhibits  no  blemishes  on  its  faces  or 
defects  in  its  substance ;  not  a  line  or  depression  is  to  be  seen  on  its  sur- 
face which  is  not  there  in  consequence  of  its  presence  in  the  impression. 
The  immediately  succeeding  operation,  although  apparently  of  great 
simplicity,  is  a  procedure  in  which  few  become  expert  and  a  less  number 
masters  :  it  is  that  of  forming  the  model  making  the  plaster  cast. 

There  are  four  primary  requisites  for  its  proper  performance  :  The 
first,  the  preparation  of  the  impression,  securing  a  uniform  and  dry  glaze 
on  its  surface,  without  destroying  any  of  its  fine  details.  Second,  the 
proper  variety  of  plaster  :  this,  when  set,  should  be  much  harder  than 
the  impression,  should  mix  readily  with  water  without  the  formation  of 
lumps,  should  set  slowly,  and  when  poured  upon  a  smooth  surface  should 
glaze.  When  hard  it  should  have  no  suggestion  of  pastiness  about  it, 
cutting  as  a  crystalline  body,  and  not,  as  inferior  plasters  do,  as  a  semi- 
glutinous  mass.  The  best  plaster  is  that  known  as  the  coarse  Eastern  ^ 
variety.  Its  particles  appear  much  coarser  than  those  of  ordinary  plaster, 
and  are  more  distinct ;  it  appears  drier ;  it  does  not  set  perfectly  for  several 
hours,  but  after  some  days  acquires  a  brick-like  hardness.  Italian 
image-makers  employ  it  for  making  casts.  Many  of  these  casts,  when 
examined,  are  seen  to  have  a  perfectly  smooth  surface,  and  yet  have 
been  made  of  the  coarse  plaster.     This  is  explained  by  the  statement 

^  Made  in  Nova  Scotia  and  Maine. 


POURING   THE  CAST.  299 

that  the  coarse  particles  are  surrounded  by  a  powdery  plaster,  which, 
when  the  mass  is  poured,  fills  the  spaces  between  the  coarser  particles. 
The  next,  the  tliird  requisite,  is  that  the  plaster  shall  be  properly  mixed 
with  water,  combined  with  it  to  form  a  paste  which  shall  be  perfectly 
smooth  and  semifluid.  The  last  requisite  is  that  this  paste  shall  be  per- 
fectly applied  to  every  portion  of  the  surface  of  the  impression.  Aside 
from  a  rough  surface  of  a  model  caused  by  improper  preparation  of  the 
impression  or  faulty  mixing  of  the  plaster  for  the  model,  the  most 
common  cause  of  blemishes  or  flaws  will  be  found  in  air-bubbles 
entangled  in  the  soft  plaster  and  leaving  spaces  upon  the  model  unfilled 
by  plaster. 

Pouring  the  Cast. — Plaster  flows  poorly  over  dry  surfaces,  so  the  sur- 
face of  the  impression  is  wet  and  the  surplus  water  shaken  out.  Should 
the  impression  have  become  unusually  dry,  it  is  immersed  until  air-bubbles 
cease  to  rise  from  it ;  this  will  render  separation  from  the  model  easier. 
As  a  preliminary  step  Dr.  Essig  advises  making  a  thin,  smooth  batter 
of  plaster,  which  by  means  of  a  camel's-hair  pencil  is  painted  into  the 
deepest  portions  of  the  impression  and  into  its  fine  lines. 

If  the  case  is  one  for  which  a  metal  plate  is  to  be  made,  the  model  is 
to  be  thicker  and  broader  than  if  the  plate  is  to  be  of  vulcanite.  Casts 
for  vulcanite  are  made  never  less  than  three-quarters  of  an  inch  thick  at 
the  thinnest  parts ;  those  for  metal  at  least  two  inches  thick.  Assuming 
that  the  model  is  to  be  for  a  metal  plate,  about  half  a  pint  of  water  is 
placed  in  a  plaster-bowl,  without  salt  or  any  substance  to  hasten  the 
setting  of  the  plaster  or  which  would  cause  deterioration  of  a  model. 
Into  the  water  plaster  is  slowly  sifted,  so  that  in  the  passage  through 
the  water  each  particle  is  wet :  the  sifting  is  continued  until  the  surface 
of  the  plaster  is  level  with  that  of  the  water ;  the  mixture  is  now  thor^ 
oughly  stirred  with  a  spatula  until  a  perfectly  smooth  paste  is  made 
which  shall  flow  freely  and  yet  not  be  too  watery.  The  impression  is 
held  in  the  left  hand,  its  distal  angle  elevated ;  the  ball  of  the  hand  is 
resting  upon  the  edge  of  the  plaster  table.  A  portion  of  the  plaster  is 
taken  upon  the  end  of  the  spatula  and  placed  at  the  elevated  heel  of  the 
impression  ;  now,  by  a  continuous  jarring  of  the  hand  upon  the  edge  of 
the  table  the  plaster  is  made  to  flow  forward,  driving  all  air  from  the 
deepest  portions  of  the  impression.  More  plaster  is  added  and  jarred 
into  place,  and  more  and  more  added  as  the  plaster  ceases  to  flow  until 
the  impression  of  the  teeth  and  that  of  the  alveolar  walls  is  filled. 
The  tray  is  now  placed  in  a  horizontal  position,  additions  of  plaster 
made  and  jarred  into  place  until  the  impression  is  more  than  full.  The 
plaster  in  the  bowl,  now  beginning  to  thicken,  is  taken  in  larger  quan- 
tities, laid  upon  the  cast,  and  thoroughly  spatulated :  the  additions 
are  made  until  the  mass  of  plaster  represents  an  inverted  pyramid, 
the  distance  from  the  edge  of  the  tray  to  the  base  of  the  pyramid  being 
about  two  inches.  The  spatula  is  passed  around  its  walls,  smoothing 
them  as  shown  by  Fig.  339,  and  the  mass  is  inverted  upon  a  piece  of 
glass  and  permitted  to  set  thoroughly. 

The  method  of  pouring  the  cast  is  the  same  irrespective  of  the  im- 
pression material.  If  this  be  of  wax  or  modelling  compound,  the  base 
of  the  cast  is  set  on  a  M^arm  stove-plate  or  upon  anything  which  shall 
now  gradually  raise  the  heat  of  the  cast  and  impression  to  something 


300  MAKING    OF  MODELS  AND   THEIR  PREPARATION. 

less  than  200°  F. .  When  the  impression  is  made  as  soft  as  when  pre- 
pared for  the  mouth,  a  finger  is  caught  under  a  lateral  border,  and  the 

Fig.  339. 


softened  material  is  drawn  entirely  away  from  the  walls  of  the  model. 
The  heel  of  the  impression  is  next  loosened  ;  then  by  steady  traction  the 
body  of  the  impression  is  withdrawn.  The  wax,  if  a  wax  impression, 
should  be  softened,  not  melted,  as  in  the  latter  case  the  surface  of  the 
plaster  becomes  infiltrated  with  the  wax. 

If  small  portions  of  modelling  compound  adhere  to  the  face  of  the 
cast,  the  softened  impression  which  has  been  removed  is  pressed  against 
them  ;  they  adhere  to  it  and  are  removed. 

With  due  care  two  casts  may  be  secured  from  one  modelling-com- 
pound impression.  One  cast  is  poured,  and  when  hard  is  set  in  cold 
water  to  below  the  edge  of  the  impression.  The  water  is  slowly  raised 
to  the  softening  heat  of  the  compound,  when  the  latter  parts  readily  from 
the  wet  cast,  being  withdrawn  by  steady  traction  in  the  direction  of  the 
axes  of  the  teeth.  Of  course  the  soaked  model  is  unfit  for  laboratory  use ; 
however,  it  may  serve  for  comparison  after  the  working  model  is  destroyed. 
The  impression  is  immediately  chilled  and  a  second  cast  poured. 

Separating  Plaster  Impressions. — In  separating  a  plaster  impression 
from  the  cast  it  is  quite  possible  by  undue  haste  or  carelessness  to  irre- 
trievably damage  the  latter.  The  practised  laboratory  workman  removes 
an  impression  from  a  cast  without  even  slight  mutilation  of  the  parts  or 
surfaces  of  the  latter,  no  matter  what  irregularity  may  be  present,  such  as 
long,  irregular  teeth  or  undercuts.  As  in  putting  together  broken  im- 
pressions, infinite  care  and  patience  are  necessary. 

The  sides  of  the  cup  are  first  freed  of  plaster,  so  that  none  of  its  edges 
interfere  with  the  removal  of  the  tray.  The  tray  is  tapped  lightly  from 
side  to  side  and  across  its  bottom  until  it  is  seen  to  loosen  from  the  im- 
pression. Should  the  latter  be  for  a  full  denture,  the  plaster  overlying 
the  alveolar  ridge  is  scraped  away  until  approach  to  the  cast  is  shown 
by  entrance  to  the  layer  of  plaster  which  has  been  colored  by  the  shellac 
varnish. 

It  has  been  recommended  to  color  the  water  into  which  the  plaster  for 


MARKING    THE  PLATE  OUTLINE.  301 

the  impression  has  been  sifted  with  aniline  red,  to  furnish  a  guide  in 
separating  the  cast  from  the  impression.'  This,  however,  does  not  pro- 
vide the  danger-signal  that  shellac  varnish  does.  The  latter,  by  coloring 
the  impression  to  a  limited  depth,  indicates  when  the  knife  is  approaching 
the  cast :  in  the  former  case  the  cast  may  be  inadvertently  marred  by  the 
abrupt  passage  from  the  red  to  the  white  plaster. 

When  the  yellow  appears  as  a  continuous  line,  the  upper  edge  of  the 
impression  is  freed  from  overlying  portions  of  the  cast :  a  small  knife- 
blade,  introduced  under  the  edges,  removes  the  outer  wall  of  the  impression 
in  pieces,  separating  it  from  the  body  of  the  impression  at  the  yellow  line. 

A  blade  introduced  beneath  its  posterior  edge  dislodges  the  body  of 
the  impression  en  masse.  If  a  full  lower  impression,  the  cast  is  cut  away 
until  all  of  the  borders  of  the  impression  are  free,  when  it  is  removed 
after  the  same  manner. 

In  separating  casts  for  partial  cases  the  first  object  is  the  perfect  free- 
ing of  the  plaster  teeth  from  the  impression  plaster.  The  highest  (most 
prominent)  parts  of  the  impression  are  scraped  away  until  the  varnish 
overlying  the  tips  of  the  teeth  is  exposed.  Beginning  at  the  masticating 
surfaces,  the  impression  is  chipped  away  piecemeal  from  the  plaster  teeth 
until  they  are  entirely  free,  and  for  more  than  a  quarter  of  an  inch  about 
the  base  of  each  tooth  the  cast  is  clear  of  impression.  The  alveolar  por- 
tions are  removed  in  sections ;  the  body  of  the  impression  may  usually 
be  detached  in  one  piece.  At  the  completion  of  the  separating  process 
the  cast  should  show  no  knife-marks. 

Trimming  the  llodel. — If  the  model  is  one  over  which  a  plate  is  to  be 
made  of  one  of  the  vegetable  bases,  it  is  cut  down  until  less  than  one 
inch  thick,  and  the  surplus  plaster  beyond  the  lines  of  the  mouth  is  cut 
away,  leaving  a  model  which  may  be  set  in  a  vulcanizing  flask  without 
requiring  further  trimming. 

If  to  be  reproduced  in  metal — that  is,  if  a  plate  is  to  be  made  of  one 
of  the  malleable  metals — and  dies  are  to  be  cast,  the  walls  of  the  model 
are  given  a  slope  at  all  its  sides,  so  that  the  broadest  part  is  its  base.  The 
thickness  of  the  model  is  not  reduced  at  all. 

Any  small  and  evident  defects  about  the  necks  of  plaster  teeth  or 
between  them  are  to  be  corrected  by  means  of  a  pointed  blade,  carefully 
trimming  out  the  portions  which  represent  the  imperfections. 

Marking  the  Plate  Outline. — Upon  the  surface  of  the  model  the  out- 
lines desired  in  the  finished  plate  are  marked.  It  is  first  determined 
what  may  be  the  extreme  limit  of  its  posterior  border.  This  must  be 
anterior  to  a  line  affected  by  the  movements  of  the  muscles  of  the  soft 
palate.  The  anterior  limit  of  movement  of  these  muscles  varies  with  the 
individual :  in  one  it  may  be  posterior  to  the  junction  of  the  maxillary 
with  the  palate  bones  ;  in  another  it  may  be  forward  of  a  line  joining  the 
condyles  of  the  alveolar  arch.  In  flat  mouths  the  line  will,  as  a  rule,  be 
found  comparatively  far  back  ;  in  high  arches  it  is  frequently  found  for- 
ward. The  limit-line  is  noted  by  having  the  patient  make  the  sound  ah! 
with  the  mouth  wide  open,  and  noting  the  line  at  which  the  muscular 
movements  of  the  palate  cease.  The  line  will  be  usually  found  at  about 
the  line  of  the  condyles ;  the  posterior  edge  of  the  plate  is  therefore 
curved  forward  from  such  a  line. 

1  Dr.  C.  W.  Spalding. 


302 


MAKING    OF  MODELS  AND   THEIR  PREPARATION. 


Fig.  340. 


The  alveolar  edge  of  the  plate  is  now  to  be  marked.  It  should 
extend  as  far  as  possible  up  the  buccal  and  lingual  aspects  of  the 
alveolar  wall,  without  impinging  upon  those  soft  parts  affected  by  the 
movements  of  the  cheeks  or  lips.  Beginning  at  the  fraenum  of  the 
upper  lip,  the  plate  line  is  marked  clear  of  this  from  the  middle  point. 
The  plate  lines  now  ascend  in  a  curve  to  about  the  positions  of  the  first 
bicuspids.  The  line  now  curves  downward  to  escape  the  anterior  edge 
of  the  buccinator  muscle,  and  ascends  again,  enclosing  the  condyles  and 
joining  the  line  marking  the  posterior  limit  of  the  plate.  In  the  mouth 
of  one  patient  these  lines  may  be  nearly  half  an  inch  above  the  alveolar 
borders  at  their  highest  points ;  in  another,  less  than  one-fourth  of  an  inch. 
The  outline  follows  that  of  the  mucous  membrane  reflected  from  the  lips 
and  cheeks  upon  the  alveolar  wall,  and  must  be  made  to  accord  with  it. 
Should  the  labial  portion  of  the  alveolar  process  be  unusually  prominent 
and  high,  so  that  no  increase  of  fulness  is  permissible,  the  natural  gum 
not  having  lost  its  normal  contour,  the  plate  is  not  carried  over  the  labial 
wall :  its  anterior  edge  is  drawn  along  a  line  which  is  that  of  the  necks 

of  the  incisor  teeth.  The  usual 
outline  for  a  full  upper  plate  is 
shown  in  Fig.  340. 

In  marking  outlines  for  a  full 
lower  plate,  it  is  to  escape,  to  be 
made  clear  of,  the  mucous  mem- 
brane reflected  from  the  cheeks, 
lips,  and  floor  of  the  mouth,  and 
to  be  cut  well  out  at  the  insertion 
of  the  frsenum  of  the  tongue.  The 
muscular  parts  of  these  regions 
carry  the  overlying  tissues  to 
higher  points  than  indicated  by 
the  model,  so  that  full  allowance 
must  be  made  in  marking  the 
plate  outline.  This  is  particularly 
notable  in  the  movements  of  the  frsenum  of  the  tongue. 

In  marking  the  outlines  of  a  partial  lower  plate,  they  are  drawn  to 
Tepresent  the  plate  resting  upon  about  one-half  the  lingual  aspects  of 
the  natural  teeth  when  these  stand  in  columns ;  when  there  are  isolated 
teeth,  these  are  generally  utilized  for  clasping  and  the  plate  is  carried 

around  their  edges.  The  same 
rules  are  observed  as  to  free- 
dom from  impingement  upon 
the  soft  parts.  When  an  iso- 
lated tooth  stands  perpendic- 
ular to  the  alveolar  arch,  the 
buccal  line  of  the  plate  is 
A'  V_       ..liisasi^  y         made  continuous,  an  opening 

being  made  in  the  plate  for  the 

passage  of  the  tooth. 

A  common  result  attending  the  wearing  of  lower  plates  accurately 

fitting  a  model  is  a  tendency  to  bury  their  buccal  edges  into  the  soft 

tissues.     The  precaution  is  taken  to  raise  this  portion  of  the  plate  from 


Position,  relative  size,  and  shape  of  vacuum- 
cavity  for  broad  palatal  arch. 


VACUUM  CHAMBERS.  303 

the  mouth,  so  that  this  tendency  becomes  impotent.  A  layer  of  wax  is 
built  over  the  outline  of  this  portion  of  the  plate  edge  about  one-eighth 
of  an  inch  deejD,  immediately  over  the  line,  and  shading  to  a  feather  edge 
where  the  wax  comes  in  contact  with  the  alveolar  wall.  Raised  from 
this  edge,  the  pressure  of  the  plate  is  greatest  at  the  height  of  the  ridge 
at  B,  Fig.  341.    This  precaution  is  always  taken  for  partial  lower  plates. 

Where  the  crest  of  the  ridge  is  represented  by  a  sharp  edge,  it  is  usual 
to  place  over  it  a  layer  of  wax  about  one-sixteenth  of  an  inch  in  thick- 
ness, the  same  precaution  to  be  taken  in  raising  the  plate  edge.  This 
throws  the  greatest  pressure  of  the  plate  upon  the  alveolar  walls.  If  not 
raised  at  the  crest,  a  plate  will  bear  too  hard  upon  the  underlying  soft 
tissues  and  cause  distress. 

Any  areas  of  the  arch  or  vault  enclosed  in  the  plate  outline  which 
represent  hard  nodular  parts  are  to  receive  a  coating  of  wax,  so  that  when 
the  soft  tissues  yield  to  the  pressure  of  the  plate,  the  latter  will  bear 
uniformly  upon  all  parts  of  its  base.  In  lower  cases  these  nodular  areas 
are  most  commonly  or  nearly  always  found  at  some  part  of  the  lingual 
aspect  of  the  alveolar  arch.  At  about  the  site  of  the  first  bicuspid  is 
the  usual  situation.  In  upper  cases  they  are  almost  invariably  found 
occupying  the  median  line  of  the  vault,  in  a  position  which  w^ould 
underlie  the  posterior  portion  of  the  plate.  They  commonly  mark  the 
junction  of  the  palatal  processes  of  the  superior  maxillary  and  palate 
bones. 

It  has  been  advised  in  such  cases  to  scrape  from  the  impression 
itself,  before  pouring  the  cast,  a  layer  of  plaster  just  thick  enough  to 
represent  the  yielding  of  the  soft  tissues.  This  method,  although  satis- 
factory in  many  cases,  alters  the  model  and  does  not  give  full  assurance 
of  accuracy,  so  that  the  method  to  be  preferred  is  to  make  a  perfect 
model  and  reverse  the  procedure  :  build  wax  over  the  prominences  to  a 
depth  equalling  the  scraping  of  the  first  method.  These  protuberances 
may  extend  so  far  forward  as  to  demand  change  in  the  configuration  of 
the  plate  outline ;  this  will  be  discussed  later. 

Vacuum  Chambers. — These  are  concavities  made  in  the  palatal 
aspect  of  the  plate  which,  when  the  plate  is  in  position  in  the  mouth, 
have  the  air  partially  exhausted  from  them,  and  the  atmospheric  pres- 
sure upon  the  lingual  surface  of  the  plate  causes  the  latter  to  adhere  to 
the  surface  of  the  vault.^  There  is  a  lack  of  harmony  of  opinion  as  to 
the  utility  of  this  device,  many  maintaining  that  its  office  is  either  but 
temporary  or  that  it  is  unnecessary.  A  majority  of  prosthetists  have, 
however,  an  abiding  faith  in  its  permanent  utility.  It  is  important  that 
these  depressions  be  properly  shaped  and  correctly  placed.  The  follow- 
ing description  will  illustrate  the  means  of  determining  their  positions  : 

The  slight  movement  usual  with  a  plate  during  mastication  tends 
to  separate  it  from  the  mucous  membrane  and  permit  the  access  of  air 
to  its  under  surface. 

The  line  of  least  movement,  as  the  movement  is  lateral,  a  rocking 
from  side  to  side,  is  along  the  median  line  of  the  vault ;  and  as  the  con- 
cavity of  the  hard  palate  is  usually  of  an  irregular  vault  form,  the  point 
of  least  movement  is  near  its  apex.  If  the  movement  does  not  extend 
to  an  edge  of  the  chamber,  the  stability  of  the  plate  is  not  materially 

^  Dental  Cosmos,  vol.  xxxvii. 


304 


MAKING    OF  MODELS  AND   THEIR  PREPARATION. 


affected,  but  when  one  of  these  edges  loses  its  contact,  air  enters  the 
chamber  and  adhesion  is  destroyed. 

The  more  closely  the  edges  of  the  chamber  approximate  this  line  the 
less  tendency  to  disturbance  there  is,  so  that  comparatively  narrow 
chambers  are  to  be  preferred ;  but  the  depression  should  be  of  sufficient 
size  to  not  materially  lessen  the  effects  of  partial  vacuum. 

Naturally,  the  chamber  should  be  in  the  area  of  greatest  stability, 
that  of  least  movement. 

This  area  will  be  found  around  and  about  the  centre  of  gravity,  and 
in  shape  resembling  the  outlines  of  the  dental  arch. 

The  dental  arch  represents,  approximately,  a  parabola  in  outline. 

This  encloses  a  trapezoid,  the  centres  of  the  cuspids  marking  the 
extremities  of  the  short,  the  centres  of  the  third  molars  those  of  the 
long,  parallel  side.  Straight  lines,  joining  these  points,  complete  the 
figure. 

The  centre  of  gravity  of  a  trapezoid  is  found  by  suspending  it  first 
by  one  obtuse  angle,  and  next  by  one  of  the  acute  angles ;  vertical  lines 
dropped  from  the  points  of  suspension  will,  in  intersecting,  mark  the 
centre  of  gravity. 

Thus,  on  the  diagram  (Fig.  342,  A,  B,  C,  D),  suspend  it  first  from  the 
angle  A,  D,  C,  and  drop  a  vertical,  D,  F. 

Suspend  from  the  angle  B,  A,  D,  and  drop  a  vertical.  A,  E.  Their 
intersection  at  the  point  G  is  the  centre  of  gravity,  which  is  posterior  to 
the  intersection  of  the  diagonals. 

Fig.  342. 


A,  B,  C,  D,  trapezoid  of  the  superior  dental  arch 
gravity  lines,  their  intersect 


G,  centre  of  gravity  of  figure ;  A,  G,  E;  D,  G,  F, 
ons  marking  G  (Burchard). 


About  the  centre  of  gravity  the  vacuum  chamber  should  be  placed, 
its  outline  following  that  of  the  arch,  on  a  smaller  scale.  In  the  vast 
majority  of  cases  the  centre  of  gravity  thus  determined  will  be  found  at 
about  the  height  of  the  vault. 

The  ends  or  apex  and  angles  of  the  chamber  should  be  about  equi- 
distant from  the  centre  of  gravity — as  a  rule,  the  apex  of  the  chamber 
as  far  in  front  of  the  intersection  of  the  diagonals  as  the  centre  of  gravity 
is  behind  that  point. 

To  apply  these  facts  practically  as  a  guide  to  finding  the  correct 
position  of  a  chamber,  draw  first  on  the  plaster  model  the  median  line 


VACUUM  CHAMBERS.  305 

of  the  vault.  From  the  centres  of  the  cuspidati  to  the  centres  of  the 
third  molars  draw  diagonal  lines,  the  diagonals  of  the  trapezoid.  When 
all  the  teeth  are  absent,  draw  from  the  positions  formerly  occupied  by 
the  cuspidati  to  the  centres  of  the  condyle  the  two  diagonals  (Fig.  343). 

Fig.  343. 


To  find  the  centre  of  gravity,  draw  from  tlie  centres  of  both  condyles 
lines  to  the  junction  of  the  first  and  second  bicuspids  of  the  opposite 
sides  other  lines,  which  intersect  at  a  point  of  the  median  line  G  ;  this 
point  will  be  the  centre  of  gravity  of  the  trapezoid  and  of  the  palatal 
vault.  The  intersection  of  the  diagonals  will  mark  the  focus  of  the 
small  parabolic  area  to  be  covered  by  the  chamber-piece.  Draw  this 
parabola,  its  apex,  about  as  far  in  front  of  the  point  of  intersection  of 
the  diagonals  as  the  centre  of  gravity  is  behind  the  latter  point,  the 
angle  of  the  parabola  the  same  distance  from  the  centre  of  gravity  as 
the  apex.  Should  there  be  a  lack  of  harmony,  of  bilateral  symmetry 
of  the  right  or  left  side  of  the  arch  outlines,  make  the  outline  of  the 
chamber  in  correspondence. 

Fig.  343  represents  a  model,  having  the  outline  of  an  old  chamber 
too  far  front ;  the  correct  position  is  marked  behind  it,  also  the  lines 
which  have  determined  its  position.  It  may  be  remarked,  parentheti- 
cally, that  an  increased  stability  was  secured  by  correcting  the  position 
of  the  chamber  in  this  case. 

To  form  the  chamber-piece,  fold  a  small  strip  of  paper,  and  lay  the 
line  of  fold  along  the  median  line  of  the  arch,  and  on  the  surface  of  the 
paper  draw  one-half  the  outline  of  the  chamber  area.  While  folded  the 
paper  is  cut  along  this  line,  unfolded,  and  is  now  the  pattern  for  the 
chamber-piece.  If  of  metal,  mark  the  shape  of  the  paper  on  the  metal 
and  cut  out,  and  fix  in  position  by  means  of  a  pin  at  the  apex  and  at 
each  angle. 

If  of  wax,  cut  from  a  sheet  of  gutta-percha  and  wax  base-plate 
(which  is  usually  too  thin  by  half  for  chambers).  Make  this  cut  firmly 
and  sharply.  Soften  the  wax  slightly,  flow  over  the  height  of  the  vault 
a  little  melted  adhesive  wax,  and  press  the  wax  chamber  into  position, 
the  outlines  of  wax  and  ])encil-marks  corresponding.  A  warmed  spatula 
is  used  to  smooth  the  edges  of  the  chamber,  which  should  be  sharp,  dis- 

20 


306 


MAKING    OF  MODELS  AND   THEIR  PREPARATION. 


Fig.  344. 


tiuct,  and  a  slight  slope  given  to  the  walls.     Chambers  which  have  not 
sharp  outlines  do  not  afford  firm  adhesion. 

I  have  followed  this  little  plan  for  at  least  ten  years,  and  in  that 
time  applied  it  to  thousands  of  cases,  and  believe  with  better  results  than 
had  haphazard  placing  of  a  chamber  been  practised. 

Plates  .should  by  all  means  be  made  without  chambers  if  without  it 
they  still  fulfil  all  the  requirements  for  a  good  piece ;  but  experience  has 
taught  that  this  result  is  the  exception,  and  not  the  rule. 

The  foregoing  description  applies  to  the  average  vault :  peculiarities 
in  the  configuration  of  the  latter  may  demand  modification  of  the  form 
or  of  the  position  of  the  chamber.  Nodular  areas  which  underlie  that 
portion  of  a  correct  plate  line,  which  the  posterior  portion  of  the  plate 
and  the  posterior  edge  of  the  chamber  would  embrace,  demand  change 

of  principle.  Where  these  protuber- 
ances are  exactly  in  this  position  a 
satisfactory  adhesion  is  occasionally 
had  by  first  covering  the  nodular  areas 
with  wax,  then  adapting  the  wax 
chamber  model,  making  its  posterior 
portion  very  shallow  (Fig.  3-14). 

Should  the  protuberance  extend 
well  into  that  portion  of  the  plate 
area  covered  by  the  vacuum  chamber, 
it  is  usually  neces.sary  to  carry  the 
])osterior  edge  of  the  chamber 
ward  of  the  anterior  edge  of 
elevation,  giving  the  heel  of 
chamber  a  concave  form  (Fig.  345). 

Should  the  elevation  lie  entirely  in  an  area  which  would  normally  be 
embraced  by  the  chamber,  a  thin  wax  chamber  model  is  cut  and  adapted 
to  cover  it,  its  edges  bearing  upon  the  soft  tissues  around  the  base  of 
the  elevation. 

In  some  instances  the  disturbing  element  may  occupy  so  much  of  the 


for- 
the 
the 


Fig.  345. 


Fig.  346. 


height  of  the  vault  that  a  median  chamber  is  inadmissible.  A  weak 
adhesion  is  secured  by  means  of  what  are  known  as  lateral  chambers 
(Fig.  346).     These  are  made  small,  oval,  and  comparatively  deep,  the 


VACUUM  CHAMBERS. 


307 


Fig.  347 


edges  nearest  to  the  height  of  the  vault  to  impinge  upon  the  soft  tissues 
at  the  base  of  the  hard  elevation. 

What  are  known  as  horseshoe  chambers  are  applicable  where  the  hard 
area  does  not  extend  too  far  forward. 

Dr.  U.  B.  Kirk  noted  in  his  practice  a  case  in  which  adhesion  could 
be  secured  only  by  the  form  of  chamber  shown  by  the  dark  shading  in 
Fig.  347. 

In  all  of  these  odd  chamber 
forms  the  walls  of  the  wax  pieces 
should  be  trimmed  at  such  an 
inclination  that  no  undercuts  are 
formed  ;  each  chamber  wall  should 
be  almost  paralled  with  the  axis 
of  the  model,  and  each  should  be 
sharp  and  distinct.  The  junc- 
tion of  the  chamber-piece  with 
the  face  of  the  model  should  be 
sharply  outlined. 

If  after  trial  in  matrix-mak- 
ing (Chapter  VIII.)  it  is  found 
the  sand  drags  about  the  wax 
chamber-piece,  the  latter  must  be 
trimmed  to  overcome  the  dif- 
ficulty :  the  angle  of  its  walls  with  its  free  surface  must  be  made  more 
obtuse. 

The  model  is  now  ready  for  the  succeeding  stages  of  preparation. 

Recalling  now  that  from  this  model  a  matrix  of  moulding  sand  is  to 
be  made — a  mould  which  shall  be  a  reverse  to  every  line  of  the  plaster 
model — it  is  evident  that  the  latter  must  be  prepared  so  that  it  may  be 
withdrawn  from  its  bed  without  breakage  or  distortion  of  the  sand. 
Bodies  of  shapes  ranging  from  those  of  cones  to  those  of  cylinders  may 
be  withdrawn  and  leave  a  true  matrix  ;  but  anything  resembling  a  re- 
versed cone  would  necessarily  break  or  disfigure  the  sand  matrix  by  its 
withdrawal. 

First,  the  model  must  be  given  a  coating  of  sandarac  varnish,  glazing 
it  faintly,  so  that  the  moulding  sand  will  not  adhere  to  it.  Next,  any 
depressions  present  at  parts  not  to  be  covered  by  the  plate  are  built  out 
to  the  pyramid  faces  by  means  of  wax  ;  as,  for  instance,  at  the  labial 
aspects  of  the  inferior  anterior  teeth  in  partial  lower  cases. 

Teeth  which  are  much  inclined  from  the  vertical  or  which  have  such 
shapes  as  would  complicate  the  moulding  operation  are  to  be  removed. 
At  about  one-sixteenth  of  an  inch  above  the  surface  of  the  model  a  saw- 
cut  half  through  tlie  plaster  tooth  is  made  ;  light  force  will  now  break 
the  attachment  of  the  tooth,  and  it  is  slipped  from  its  pin  support.  The 
sharp  line  of  fracture  furnishes  a  guide  in  replacing  the  tooth  after  the 
dies  are  made. 

It  is  occasionally  designed,  particularly  for  plates  having  all  or  part 
of  the  artificial  gum  formed  of  vulcanite,  to  form  the  alveolar  edge  of  the 
plate  into  a  rim.  This  form  of  rim  is  always  employed  with  continuous- 
gum  dentures.  The  method  of  preparing  the  model  for  this  variety  of 
dentures  will  be  described  in  Chapter  XIII,  on  Continuous-gum  Work. 


308 


MAKING    OF  MODELS  AND   THEIR  PREPARATION. 


The  edge  of  the  rim,  marking  the  height  of  the  plate,  must  be  at  a  line 
which  shall  ensure  against  reducing  the  plate  after  it  is  finished.  At 
about  one-sixteenth  of  an  inch  beneath  the  usual  plate  outlines  a  wall  of 
wax  is  applied  to  the  alveolar  border  of  the  model :  the  angle  which  this 
wax  forms  with  the  alveolar  wall  should  not  be  more  than  a  right  angle, 
and  if  possible  it  should  be  acute.  The  ledge  of  wax  is  made  perfectly 
smooth  and  clear  cut:  it  should  be  something  more  than  one-eighth  of  an 
inch  broad.  Its  outer  wall  is  to  merge  into  the  general  walls  of  the  model. 

Fig.  348. 


Cast  of  upper  jaw,  ready  for  moulding     The  model  for  the  \  acuum-chamber  is  in  position. 


The  experience  of  many  skilled  prosthetists  has  demonstrated  an  ad- 
vantage to  be  gained  through  a  judicious  alteration  of  the  face  of  a  model. 
Vaults  which  exhibit  defined  areas  of  differing  density  are  subjected  to 
uneven  pressure  by  a  plate  which  is  perfectly  adapted  to  an  accurate 
model.  It  is  recommended  that  a  careful  topographical  examination  be 
made  of  the  vault,  and  those  portions  found  to  be  soft  are  to  have  the  cor- 
responding areas  of  the  model  scraped  away  as  much  as  they  will  yield 
to  the  pressure  of  the  plate.  The  portions  to  be  trimmed  are  commonly 
in  the  height  of  the  vault  at  both  sides  of  the  median  line  :  between  the 
apex  of  the  vault  and  the  beginning  of  its  walls  at  their  posterior  portions 
will  be  found  in  most  mouths  areas  softer  than  the  other  aspects  of  the 
vault.  This  method  is  particularly  applicable  for  mouths  where  it  is 
designed  to  construct  a  plate  without  a  vacuum  chamber. 


CHAPTER   VIIT. 

DIES,  COUNTER-DIES,  AND  MOULDING. 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 


A  DIE  is  the  duplication  of  a  model  in  metal  made  to  facilitate  the 
formation  of  some  resistant  substance  into  a  plate  which  shall  be  per- 
fectly adapted  to  the  surface  of  the  model. 

A  counter-die  is  the  female  die,  formed  by  pouring  over  the  surface 
of  the  die  a  defined  block  of  a  metal  or  alloy  more  fusible  than  the  die. 

The  operation  of  moulding  consists  in  forming  in  sand  or  any  suitable 
medium  a  matrix  which  shall  represent  accurately  a  reverse  impression 
of  the  plaster  model :  the  die  is  formed  by  filling  the  matrix  with  molten 
metal. 

The  purpose  of  the  latter  operation  and  the  implements  produced  by 
it  is  the  securing  of  two  metallic  blocks  of  sufficient  rigidity  to  permit 
the  forming  between  them  of  a  sheet  of  metal  of  a  size,  sliape,  and  variety 
suitable  to  serve  as  a  supporting  base  to  an  artificial  denture — a  lamina 
which  shall  be  perfectly  adapted  to  the  surfaces  of  the  alveolar  ridge  and 
palatal  vault. 

Moulding  Sand. — Three  varieties  of  sand  are  used  in  the  dental 
laboratory  for  making  matrices.  The  first  and  oldest  is  the  finest  grade 
of  iron-founder's  black  sand  ;  the  second,  the  brass-moulder's  brown  sand ; 
and  third,  marble  dust.  The  last  is  used  perhaps  more  frequently  tlian 
either  of  the  others  :  it  is  no  better  than  the  second  variety — indeed,  the 
writer  believes  the  brass-moulder's  sand  gives  the  best  matrices. 

A  sand  for  this  purpose  should  be  fine-grained  enough  to  give  a 
smooth  surface  to  metals  poured  over  it,  and  yet  possess  sufficient  poros- 
ity when  packed  in  a  moulding  ring  to  permit  the  escape  of  steam  formed 
when  molten  metal  is  poured  in  a  moist  matrix,  and  should  form  a  mass 
of  sufficient  coherence  to  maintain  a  given  form  and  to  permit  the  with- 
drawal of  a  prepared  model  from  it  without  fracture.  Marble  dust 
has  the  two  advantages  of  being  more  cleanly  and  retaining  moisture 
longer. 

Preparing  the  Sand. — Upon  the  preparation  of  the  moulding  sand  will 
depend  much  of  the  success  of  die-making.  The  sand  should  be 
moistened  uniformly  and  sufficiently  to  give  a  sharp  line  of  fracture 
when  a  mass  made  by  squeezing  in  the  hand  is  broken,  and  yet  be  in 
such  a  condition  that  it  will  readily  pass  through  the  meshes  of  a  fine 
flour-sieve.  To  attain  or  produce  this  condition  care  and  deliberation 
are  necessary.  Twenty  minutes  is  none  too  short  a  time  in  which  to 
properly  prepare  three  quarts  of  sand. 

309 


310  DIES,    COVNTEB-DIES,   AND  MOULDING. 

About  a  gallon  of  the  sand  is  placed  at  one  end  of  the  sand-tray  and 
gradually  drawn  toward  the  operator  by  means  of  the  sand-crusher,  pul- 
verizing any  lumps  which  may  be  present.  It  is  now  sifted,  and  hard 
lumps,  fragments  of  zinc,  lead,  or  other  foreign  materials  thus  separated 
are  cast  aside.  The  sand  is  spread  over  the  floor  of  the  sand-tray  in  an 
even  layer,  and  sprinkled  with  about  half  a  pint  of  water ;  it  is  then 
stirred  and  tossed  with  a  broad  wooden  spatula,  and  then  thoroughly 
rubbed  with  the  sand-crusher  for  fifteen  minutes  or  more,  then  sifted. 
The  sieved  sand  should  be  tested  by  compressing  a  quantity  in  the  hand  ; 
it  should  break  with  a  sharp  line  of  fracture. 

There  is  an  indescribable  feel  to  properly  prepared  moulding  sand 
with  which  the  experienced  moulder  becomes  familiar. 

It  has  been  recommended  to  substitute  oil  for  water  in  the  preparation 
of  moulding  sand,  as  the  sand  so  prepared  is  always  ready  for  use.  This 
single  advantage  does  not  compensate  for  the  dirty  working  of  the 
material  tempered  by  that  medium.  Its  odor  when  heated  by  the  molten 
metals  is  also  objectionable. 

Metals  Used  for  Dies  and  Counter-dies. — The  prepared  model  is  to 
be  reproduced  in  some  metal  which  possesses  the  following  character- 
istics :  It  should  be  hard  enough  to  withstand  the  force  of  swaging  with- 
out marked  bruising  of  its  surface ;  it  should  be  tough  and  not  brittle, 
so  that  it  will  not  break  ;  the  degree  of  contraction  should  be  low — 
that  is,  the  mass  should  shrink  but  little  upon  solidifying ;  finally,  it 
should  be  readily  fusible  in  the  common  heating  appliances  of  the 
laboratory,  and  when  molten  should  possess  a  quick  fluidity  which  shall 
permit  of  its  flowing  freely  into  small  spaces.  Of  all  the  available 
metals,  zinc  alone  possesses  these  several  features,  and  is  therefore  in 
general  use  for  the  making  of  dental  dies.  The  alloys  of  zinc  do  not 
answer  as  well  for  this  purpose.^ 

The  alloy  known  as  Babbitt  metal  is  frequently  used  for  die-making. 
It  has  a  lower  index  of  contraction  than  zinc,  is  more  fusible,  and  is  more 
brittle.  Plates  made  upon  dies  of  this  alloy  fit  the  plaster  model  as  they  fit 
the  die.  In  lower  plates,  particularly  those  for  partial  lower  dentures,  or 
clasp  plates  for  the  upper  jaw,  this  is  a  desirable  feature.  Prof.  C.  J. 
Essig^  regards  the  contraction  of  zinc  as  being  a  strong  feature  of  recom- 
mendation for  use  in  making  dies  for  full  upper  dentures,  for  "  it  Avill  be 
noticed  that  a  plate  fitted  to  a  zinc  die  is  found  to  be  in  close  contact 
with  the  plaster  model  throughout  the  alveolar  walls,  but  at  the  pos- 
terior edge  it  is  short  of  contact ;  thus  the  greatest  pressure  is  upon  the 
ridge,  and  the  danger  of  resorption  of  the  tissues  of  the  vault  is  avoided. 
With  the  greatest  pressure  along  the  ridge  absorption  occurs,  but  in  the 
parts  underlying  those  in  which  resorption  is  merely  a  physiological 
process.  HoM^ever,  plates  perfectly  fitting  to  zinc  dies  when  placed  in 
the  mouth  are  found  to  have  accurate  adaptation ;  the  expansion  of  the 
plaster  compensates  sufficiently  for  the  contraction  of  the  zinc,  and  again 
the  yielding  of  the  soft  tissues  brings  the  plate  in  contact  throughout 
its  area. 

The  zinc  of  commerce  contains  a  variable  amount  of  impurities  : 
samples  derived  from  the  ores  of  several  localities  show  an  inconstancy 

^  Essig's  Metallurgy.  ^  See  Chapter  II. 


PROCESS  FOR  STAMPING  PLATES  BY  HYDRAULIC  PRESS.   311 

of  physical  properties  when  formed  into  dies.  The  variety  known  as 
Bertha  zinc  appears  to  be  about  the   toughest  and  most  homogeneous. 

There  are  many  formulas  published  of  alloys  to  which  are  given  the 
general  title  of  Babbitt  metal.  The  formula  best  adapted  for  dental 
purposes  is  that  of  Dr.  L.  P.  Haskell :  containing  the  ratio  of  tin  that 
it  does,  it  is  comparatively  expensive,  but  the  cheaper  specimens  are  not 
serviceable  as  dies. 

The  alloy  known  as  Babbitt  metal  is  composed  of  tin,  72.72  ;  copper, 
9.09  ;  antimony,  18.18.  The  alloy  is  largely  a  mechanical  mixture.  In 
melting  it  is  seen  that  a  portion  becomes  fluid,  in  which  are  suspended 
the  crystals  of  the  more  refractory  metals.  In  solidifying  the  base  of  a 
die  is  seen  to  exhibit  distinct  evidence  of  the  differences  of  points  of 
crystallization,  one  portion  crystallizing,  while  others  are  still  fluid. 

For  small  dies  the  bismuth  or  cadmium  alloys,  known  as  fusible 
metals,  are  occasionally  used :  they  are  very  brittle,  entirely  too  frangible 
to  withstand  any  but  light  blows. 

Compounds  known  as  Spence's  metal  have  been  in  very  limited  use 
for  the  making  of  dies.  They  are  sulphides  of  metals,  dissolved  by 
heating  in  an  excess  of  sulphur. 

The  mixture  and  the  method  of  using  are  described  by  Dr.  E.  H. 
Bog  Lie : 

"Description  of  Process  for  Stamping-  Plates  by  Hydraulic  Press.^ 
— Within  a  few  years  a  material  called  Spence  metal  has  been  devised. 
This  substance  is  really  sulphur  and  iron.  It  melts  at  about  the  boiling- 
point  of  water,  and  in  process  of  cooling  a  stage  is  reached,  just  before 
solidification  takes  place,  at  which  the  mass  becomes  exceedingly  fluid. 
At  this  stage  it  can  be  poured  into  an  impression  of  plaster  or  even 
Stent's  composition. 

"  This  circumstance  has  caused  Spence  metal  to  be  used  in  the  hy- 
draulic press  for  the  purpose  of  stamping  dental  plates,  as  a  steady  pres- 
sure of  almost  any  power  may  be  had  by  this  means.  It  is  also  possible 
to  make  the  dies  and  stamp  a  plate  within  two  hours  from  the  time  of 
taking  the  impression.  A  description  of  a  case  in  hand  will  perhaps 
best  serve  my  purpose.  In  the  present  instance  an  impression  was  taken 
with  Stent's  material,  and  all  the  rest  of  the  work  was  done  by  my  friend 
and  assistant,  Mr.  Fred.  Collett.  The  impression  was  chilled  with  cold 
water,  and  sculptor's  clay  was  built  up  around  the  margins  to  the  height 
of  half  an  inch.  A  paper  could  have  been  wrapped  around  equally  well. 
The  impression  then  was  coated  with  a  solution  of  soap  and  water.  Into 
this  impression,  thus  prepared,  Spence  metal,  just  before  the  point  of 
solidification,  was  poured.  This  Spence  metal  was  chilled  immediately 
on  touching  the  Stent's  composition,  so  that  all  contraction  took  place 
from  the  top  of  the  centre  downward. 

"  The  small  die  thus  made  was  then  provided  with  three  legs  made  of 
pins  heated  and  pressed  into  the  metal.  These  pins  held  it  at  just  the 
required  height,  so  that  the  die,  being  placed  in  the  middle  of  the  iron 
ring  in  which  the  pressure  was  to  be  given,  stood  at  the  height  required 
for  an  additional  quantity  of  Spence  metal  to  be  poured  into  the  con- 
cavity and  around  this  little  die  up  to  the  required  level.     This  die, 

*  Read  at  the  semi-annual  meeting  of  the  Massachusetts  Dental  Society,  Boston,  June 
6,  1889,  International  Dental  Journal,  July,  1889. 


312  DIES,    COUNTER-DIES,   AND  MOULDING. 

being  quite  cold,  is  covered  with  whiting,  and  a  counter-die  of  Wood's 
fusible  alloy  ^  is  poured  over  it.  This  fusible  alloy  melts  at  a  still  lower 
temperature  than  Spence  metal,  and  it  is  poured  over  the  male  die  by 
using  the  heavy  iron  ring  in  which  the  counter-die  must  remain  during 
the  swaging  process.  This  first  set  of  dies  being  completed,  dupli- 
cates are  made,  if  required,  by  taking  the  impression  of  the  male  die 
and  repeating  the  process  of  casting  the  dies  as  often  as  may  be 
required. 

"  The  Spence  metal  is  exceedingly  brittle,  so  nothing  but  steady  pres- 
sure nnist  be  permitted.  If  it  should  be  found  necessary  to  use  succes- 
sive force,  others  must  be  made  of  some  other  material.  In  the  present 
instance  a  Babbitt's-metal  die  with  a  tin  counter-die  was  made  upon  which 
to  break  up  the  plate. 

''  The  flat  plate  may  be  placed  between  the  dies  with  a  bit  of  giove-kid 
or  rubber  dam  between  the  plate  and  the  counter-die,  and  the  flask  con- 
taining it  placed  directly  in  the  press.  The  screw  at  the  top  of  the  press 
being  turned  down  to  give  such  pressure  as  is  possible  from  above,  the 
second  screw  connected  with  the  plunger  at  the  side  is  then  gradually 
turned  inward  by  means  of  the  large  driving-wheel.  The  manometer  is 
watched,  as  indicating  the  amount  of  pressure  that  is  being  given  ;  four 
hundred  pounds  to  the  square  centimetre  is  generally  enough,  though  I 
have  as  an  experiment  run  it  up  to  twelve  hundred. 

"  During  the  swaging  process  the  plate  should  be  frequently  annealed. 
When  finally  down,  close  to  the  duplicate  dies,  it  receives  its  last 
trimming,  its  last  annealing,  and  is  then  put  upon  the  original  die  that 
was  made  directly  from  the  impression.  When  taken  from  the  press 
after  this  final  pressure,  the  fit  is  more  perfect  than  any  struck  swages 
can  make  it. 

"  For  suction-plates  it  is  generally  necessary  to  scrape  the  centre  of 
the  plaster  impression  and  not  to  put  in  an  air-chamber,  the  fit  of  the 
hydraulic-press  plates  seeming  to  be  as  good  as  the  impressions  from 
which  they  are  made." 

The  material  and  method  have  not  been  adopted  ;  but  such  a  com- 
pound would  serve  well  for  the  making  of  very  small  dies  to  which 
much  force  is  not  to  be  applied. 

For  general  use  zinc  is  to  be  employed  for  the  dies  for  full  upper 
plates  and  for  the  primary  dies  of  all ;  Babbitt  metal  is  most  useful 
for  making  the  finishing  dies  of  all  partial  cases  and  for  full  lower 
plates,  and  also  the  finishing  dies  for  the  full  upper  plates  occasionally 
made  without  vacuum  chambers. 

Metals  for  Counter-Die^. — The  metals  in  use  for  making  counter-dies 
are  lead,  an  alloy  of  lead  and  tin,  and  zinc. 

When  molten  these  metals  may  be  poured  upon  a  zinc  die  without 
fusing  the  face  of  the  latter,  provided,  of  course,  their  temperature  be 
not  too  high.  Lead,  because  of  its  softness,  is  used  as  a  counter  to  the 
first  die,  and  it  may  be  for  the  second  or  third  die  also  ;  but  the  lead- 
and-tin  alloy,  being  harder,  is  to  be  preferred  for  the  final  swaging. 

Zinc  is  used  as  a  counter-die  for  those  cases  presenting  very  deep  and 

^  Composed  of  15  parts  of  bismuth,  8  of  lead,  4  of  tin,  and  3  of  cadmium.  This 
forms  a  silvery-white,  gi-annlar  allov,  which  becomes  soft  at  135°  F.  (=  57°  C),  and  fuses 
at  about  145°  F.  (=  63°  C). 


MOULDINO  FLASKS. 


313 


irregular  rugce  ;  also  for  swaging  platinous  gold.  The  leacl-and-tin  alloy 
is  employed  as  a  counter  for  dies  of  Babbitt  metal.  Type  metal  may  be 
employed  for  the  same  purpose. 

Moulding"  Flasks. — The  moulding  flasks  of  the  dental  laboratory 
have  the  forms  of  rings  which  have  been  flattened  upon  one  side,  corre- 
sponding with  the  general  outline  of  the  plaster  model.  They  are  made 
of  several  sizes,  telescoping  one  over  another.  The  largest  sizes  are  used 
for  enclosing  the  matrix,  the  smaller  to  deepen  the  matrix  cavity  and 
thus  give  increased  thickness  and  strength  to  the  die.  A  set  known  as 
the  Bailey  flasks  is  in  general  use  (Figs.  349-351). 


Fig.  349. 


Fig.  350. 


Fig.  351. 


Bailey's  flasks. 


Dr.  Uriah  B.  Kirk,  an  expert  prosthetist,  many  years  ago  introduced 
as  moulding  rings  sections  of  heavy  five-inch  stovepipe,  having  riveted 
joints.  These  sections  answer  admirably,  as  there  is  less  danger  of  pack- 
ing too  tightly  the  large  mass  of  sand  contained  in  them  than  were  the 
mass  smaller.  The  writer  has  for  several  years  used  them  with  greater 
satisfaction.     They  are  made  about  five  inches  deep. 

A  sectional  cylinder,  known  as  the  Hawes  flask  (Figs.  352-354), 
is  commonly  employed  for  moulding  cases 
presenting  marked  alveolar  undercuts. 

Moulding". — The  prepared  sand  is  placed 
to  one  side  of  the  sand-tray ;  the  model  is 
set  upon  the  zinc  floor,  and  a  large  moulding 
ring  is  placed  around  it,  using  a  size  which 
shall  clear  the  model  on  all  sides  at  least  half 
an  inch.  A  pint  or  more  of  the  sand  is 
placed  in  a  flour  sieve  and  sifted  over  the 
face  of  the  model,  adding  more  and  more  until  the  ring  is  about  half 
full ;  then,  using  the  tips  of  the  fingers,  the  sand  is  pressed  on  and 
about  the  model  until  it  is  packed  firmly  ;  more  sand  is  added  until  the 


Fig.  353. 


Fig.  354. 


ring  is  more  than  full :  it  is  pressed  down  firmly ;  then,  using  a  broad 
sharp  spatula  or  table  knife,  the  sand  is  trimmed  level  with  the  top  of 
the  flask. 


314 


DIES,    COUNTER-DIES,   AND  MOULDING. 


The  ring  is  now  inverted  and  placed  upon  the  floor  of  the  sand-tray ; 
an  old  excavator  having  a  tapering  point  is  gently  driven  into  the  centre 
of  the  base  of  the  model,  and  serves  as  a  handle  by  which  to  withdraw 
the  model  from  its  sand  bed.  Using  the  handle  of  the  smoothing  knife 
as  a  percussing  tool,  the  model  is  lightly  tapped  on  all  sides  until  it 
begins  to  loosen  ;  then,  grasping  the  projecting  handle,  a  gentle  traction 
is  exerted  upon  the  model,  continuing  the  tapping,  and  the  model  is 
withdrawn.  Another  method  of  detachment  is  by  holding  the  base  of 
the  model  over  a  bed  of  sand  made  to  receive  it;  it  is  tapped  until  it 
falls  from  the  matrix.  Another  is  to  loosen  the  model  by  tapping  upon 
alternate  sides,  then  inverting  over  the  sand  bed  and  permitting  the 
model  to  drop  out.  The  first  method  described  is  to  be  preferred,  as 
there  is  less  danger  of  disturbing  the  matrix. 

The  mould  is  now  examined  :  if  it  exhibits  a  coarse,  porous  surface, 
if  any  portions  have  broken  away,  which  may  be  noted  by  ragged  sur- 
faces to  any  part  of  the  matrix,  it  is  to  be  rejected,  and  the  moulding 
operation  repeated  until  at  least  two  good  moulds  are  obtained. 

If  the  case  be  one  in  which  teeth  are  remaining,  see  that  the  outlines 
of  each  tooth  be  distinct,  and  also  the  lines  between  the  teeth.  Any  teeth 
standing  in  such  positions  as  to  cause  dragging  of  the  sand  in  withdraw- 
ing the  model  from  the  matrix  are  to  be  removed  before  the  moulding. 

There  are  cases  in  which,  despite  repeated  attempts,  good  moulds  are 
not  secured.  One  class  of  these  cases  is  formed  of  those  having  an 
overhanging  alveolar  ridge,  particularly  at  its  anterior  portion.  If  the 
undercut  be  not  too  marked,  the  front  of  the  walls  may  be  raised,  bring 
the  axis  of  this  portion  of  the  ridge  nearer  to  a  vertical  line.     An  in- 

FiG.  355. 


clined  bed  of  sand  is  made,  the  front  of  the  model  resting  upon  its 
highest  portion,  the  heel  of  the  model  upon  the  floor  of  the  sand-tray : 
it  is  enclosed  by  a  moulding  ring,  the  sand  packed  as  described,  the  ring 
inverted,  the  base  of  the  metal  freed  from  sand,  and  it  is  then  detached 
by  holding  it  over  a  sand  bed  and  tapping  :  by  this  means  moulds  of 
undercut  cases  may  usually  be  secured.     If  the  mould  be  accurate,  the 


CORE-MO  ULDING. 


315 


sand  in  the  ring  is  trimmed  to  a  flat  surface,  A,  B.  The  matrix  and 
ring  are  then  set  on  an  inclined  bed  of  sand,  so  that  the  line  C,  D  is 
almost  or  quite  horizontal. 

The  undercut  may  be  so  marked  that  this  expedient  does  not  suffice, 
the  sand  breaking  away  at  the  part  of  the  mould  corresponding  to  the 
undercut.  The  device  known  as  the  Hawes  flask  is  now  in  order.  The 
model  if  too  thick  should  be  trimmed  away  at  its  base  until  the  surface 
of  the  alveolar  ridge  is  level  with  the  jointed  section.  This  section, 
with  the  pins  fastening  it,  is  placed  in  position  about  the  model,  and 
sand  packed  about  the  latter.  The  surface  of  the  sand  is  made  level, 
and  powdered  charcoal  or  talc  dusted  over  it  to  prevent  the  sand  of  the 
superimposed  section  from  adhering  to  it.  The  second  section  is  placed 
in  position  and  filled  with  sand,  well  packed  and  its  surfaces  trimmed 
flat.  The  second  section  is  removed  and  placed  upon  a  flat  surface. 
The  pin  holding  the  sectional  cylinder  together  is  removed,  and  the 
cylinder  is  then  carefully  opened  sufficiently  to  permit  removal  of  the 
model.  The  cylinder  is  closed,  the  pin  placed  in  its  opening,  and  the 
second  cylinder  set  in  position  over  the  first.  Much  care  is  required 
to  secure  accurate  moulds  with  this  device,  and  it  may  be  the  dernier- 
ressort  of  the  moulder  will  be  necessary — the  operation  known  as  core- 
moulding. 

Core-moulding. — At  the  site  of  the  undercut  the  varnished  surface 
of  the  model  is  oiled.  A  batter  of  2  parts  marble  dust,  pumice,  or 
beach  sand  and  1  part  plaster  is  used  to  extend  the  wall  of  the  model 
to  the  shape  of  a  larger  pyramid.     When  this  has  set  it  is  carefully 

Fig.  356. 


detached  from  the  model,  its  external  wall,  upper  and  lower  surfaces 
smoothed  by  means  of  sand-paper,  then  thoroughly  dried  over  a  stove  : 
if  used  wet,  bubbling  of  metal  in  contact  with  it  will  ensue.  When  it 
is  cold  it  is  placed  in  position  on  the  model,  and  its  outer  surface  and 
top  are  varnished.  When  the  varnish  has  hardened,  a  mould  is  made 
which  must  be  perfect,  the  outlines  of  the  core  being  plainly  marked. 
The  core  is  removed  from  the  model  and  placed  in  its  position  in  the 
matrix,  and  its  edges  luted  to  the  latter  by  wetting  the  sand  along  the 
line  of  junction.     The  matrix  is  dried  before  pouring  metal  into  it. 

Occasionally  it  is  necessary  to  use  cores  for  limited  undercuts  at  the 
lingual  aspect  of  lower  cases.  They  are  to  be  used  in  all  cases  where 
it  is  impossible  to  secure  an  excellent  matrix  without  them.  Usually  a 
matrix  accurate  enough  for  the  starting  die  may  be  made  by  the  ordi- 


316  DIES,   COUNTEB-DTES,   AND   MOULDING. 

nary   method,    tlie   core   used    for    the    matrix    of   the    finishing    dies. 
Imperfect  dies  are  to  be  trimmed  as  described  later. 

A  smoother  surface  may  be  given  the  matrix  and  die  by  "  sooting " 
the  surface  of  the  former,  holding  it  over  the  flame  of  a  candle. 

Making-  Dies. — The  ladles  in  which  die  and  counter-die  metals  are 
melted  should  be  plainly  marked,  to  avoid  mixing  the  latter.  About  three 
pounds  of  fine  zinc  ingots  are  placed  in  a  ladle  and  melted  in  any  of  the 
laboratory  furnaces.  Where  gas  is  not  obtainable  excellent  gasoline 
melting  furnaces  may  be  used  (see  pages  25  and  26).  The  zinc  is  to  be 
entirely  molten  before  pouring ;  if  used  before  it  is  perfectly  fluid,  or 
rather  while  an  unmelted  core  remains  in  it,  bubbling  is  almost  certain 
to  occur.  If  raised  to  too  high  a  temperature,  the  zinc  produces  brittle 
dies.  If  old  dies,  and  not  zinc  ingots,  have  been  used,  a  quantity  of 
scrap  wax  is  thrown  upon  the  molten  metal,  and  it  is  well  stirred,  disen- 
tangling the  oxides,  which  then  float  upon  the  surface  and  are  skimmed 
ofl"  before  the  zinc  is  poured. 

When  perfectly  fluid  the  zinc  is  poured  into  the  matrix,  holding  the 
mouth  of  the  ladle  quite  close  to  the  ring.  The  matrix  is  poured  nearly 
full ;  a  smaller-sized  moulding  ring  is  set  around  the  matrix  and  resting 
upon  the  sand  :  this  is  poured  full  or  nearly  full  to  give  increased  weight 
and  strength  to  the  die.  In  about  five  minutes  the  die  and  enclosing 
parts  are  freed  from  sand.  The  die  is  now  examined  for  any  imperfec- 
tions :   these  when  found  are  remedied  by  trimming  with  a  sharp  chisel. 

The  zinc  when  hot  may  be  cut  as  readily  as  half-set  amalgam  ;  if  per- 
mitted to  cool,  trimming  is  difficult.  The  second  die  is  examined,  and 
the  better  one  of  the  two  is  reserved  for  a  finishing  die.  If  the  case  be 
one  for  a  partial  denture,  the  zinc  teeth  of  the  starting  die  are  cut  off"  by 
means  of  a  small  cold  chisel  to  within  one-sixteenth  of  an  inch  of  the 
surface  of  the  model,  leaving  a  sharp  edge  to  the  stumps,  so  as  to  mark 
the  plate  in  swaging. 

If  for  a  partial  lower,  the  teeth  on  the  first  die  are  cut  off"  to  just 
above  the  plate  line,  and  at  an  acute  angle.  As  a  rule,  the  teeth  should 
remain  on  the  finishing  die. 

If  the  dies  are  of  Babbitt  metal,  the  metal  must  be  perfectly  fluid 
before  pouring  :  when  the  matrix  is  full  a  second  ring  is  placed  over  it, 
and  about  a  half  inch  of  the  molten  metal  poured  in  this,  and  the  die  is 
permitted  to  partially  set  before  further  addition  is  made.  As  stated 
before,  this  alloy  is  in  great  part  a  mixture,  not  a  chemical  compound,  of 
the  several  metals,  so  that  the  most  fusible  constituents  remain  fluid  for 
some  time  after  the  more  refractory  metal  or  alloy  has  set :  if  too  much 
be  poured,  the  fluid  portions  ooze  from  beneath  the  upper  ring.  Dies 
of  this  metal  should  be  made  very  thick,  as  the  alloy  is  much  more  brittle 
than  zinc.  They  should  remain  undisturbed  until  it  is  seen  from  the 
surface  that  solidification  is  complete.  They  are  to  receive  any  necessary 
trimming  while  hot,  and  to  be  perfectly  chilled  and  dried  before  pouring 
the  counter-die. 

Counter-dies. — The  cooled  dies  are  freed  from  sand,  and,  if  they  have 
been  chilled  by  placing  in  cold  water,  wiped  perfectly  dry.  Serious  acci- 
dents have  occurred  through  pouring  molten  lead  upon  wet  dies.  The 
steam  confined  between  the  two  metals  expands  with  explosive  force  and 
drives  out  and  scatters  about  the  molten  lead. 


COUNTER-DIES. 


317 


Enough  sand  is  placed  in  a  large  moulding  ring,  which  has  been  in- 
verted, to  bring  the  plate  line  of  the  die  a  little  higher  than  the  edges  of 
the  ring ;  sand  is  packed  about  the  die  level  with  the  edge  of  the  ring. 
Around  and  over  the  die  is  placed  another  moulding  ring. 

Babbitt-metal  dies  and  those  which  are  to  have  zinc  counters  made 
over  them  are  to  have  their  surfaces  blackened  over  an  oil  or  gas  flame, 
to  prevent  adhesion  of  the  counter-die  metals. 

Counter-die  metals  are  to  be  poured  as  soon  as  fluid.  The  tempera- 
ture of  molten  lead  is  to  be  tested  by  thrusting  into  it  a  wisp  of  paper : 
if  it  merely  browns  the  paper,  it  is  at  the  proper  temperature  ;  if  it 
carbonizes  or  ignites  it,  it  is  too  hot. 

The  lead-and-tin  alloy,  the  counter-die  metal  used  with  Babbitt-metal 
dies,  is  to  be  poured  while  a  small  portion  of  it  is  still  unmelted.  Zinc 
for  counter-dies  is  poured  while  a  portion  is  still  unmolten.  When  fluid 
the  metal  is  poured  in  a  small  stream,  but  rapidly,  until  the  ring  is  full. 

In  pouring  counters  for  Babbitt-metal  dies  or  in  making  zinc  counter- 
dies  do  not  permit  the  molten  metal  to  fall  from  a  height  upon  one  point 
of  the  die  ;  it  tends  to  fuse  that  spot  of  the  latter. 

When  the  counter-die  has  set  the  mass  is  freed  of  sand  and  chilled 
in  cold  water.  The  die  and  counter  are  separated  by  drawing  blows 
delivered  upon  the  base  of  the  die. 

The  counter-dies  are  then  set  upon  an  avil,  the  dies  adjusted  to  them, 
and  they  are  driven  together  by  blows  of  a  swaging  hammer.     In  cases 


Die  and  counter-die. 


which  present  an  unusually  high  vault  and  ridge  it  is  advisable  to  use 
partial  counter-dies  to  form  the  vault  portion  of  the  plate  before  any 
attempt  is  made  to  form  that  portion  covering  the  ridge  and  outer  alveolar 
wall.  The  writer  has  for  ten  years  used  a  graded  set  of  these  partial 
counters  for  this  purpose. 

For  the  largest  the  die  is  imbedded  in  sand  to  the  level  of  the  sum- 


318  DIES,    COUNTER-DIES,   AND  MOULDING. 

mit  of  the  ridge,  and  a  counter-die  poured  as  described.  When  this  has 
been  separated  two  or  more  pyramidal  masses  of  lead,  covering  the 
height  of  the  vault  and  about  two  inches  high,  are  poured,  almost  drop 
by  drop.  These  extend  about  half  an  inch  beyond  the  borders  of  the 
vacuum  chamber.  The  several  dies  and  counter-dies  are  marked  at 
their  heels  to  designate  the  dies  and  counter-dies  which  belong  together. 
They  are  brushed  clean  before  using  them.^ 

The  methods  described  are  those  commonly  practised,  and  which  have 
survived  the  test  of  time.  Other  methods  for  making  dies  have  been  ad- 
vocated, but  they  are  more  the  nature  of  curiosities  at  this  day  than 
applied  methods. 

One  of  these  processes  is  die-making  by  dipping.  The  plaster  model 
has  its  chamber-piece  made  of  plaster,  and  is  left  unvarnished.  A 
sheet-iron  basin  some  four  or  five  inches  in  diameter,  smaller  at  the  base 
than  across  its  uncovered  top,  is  filled  with  molten  zinc  ;  in  this  the  face 
of  the  unvarnished  model  is  thrust  to  above  the  plate  outlines.  When 
the  metal  has  set  the  plaster  is  removed,  the  model  being  destroyed  in 
removal.  Around  the  depression  representing  the  counter-die  a  mould- 
ing ring  is  placed,  and  the  die  is  made  of  a  metal  more  fusible  than  the 
counter-die.  The  counter-die  may  be  smoked,  and  the  die  made  of 
zinc  also. 

Occasionally  dies  have  been  made  of  the  bismuth  alloys  called  fusible 
metals.  The  sides  of  the  impression  being  enclosed  with  a  putty  wall  of  the 
proper  height,  the  molten  metal  is  poured  directly  into  the  plaster 
impression. 

Dr.  B.  W.  Franklin^  devised  the  means  of  securing  counter-dies 
when  this  alloy  is  used  for  tlie  die.  A  sheet-lead  plate  is  burnished  and 
pressed  to  fit  the  die  ;  this  is  filled  with  moulding  sand  and  set  upon  a 
bed  of  the  latter ;  around  it  a  moulding  ring  is  set,  and  a  counter-die 
made  of  tin  or  a  low-flowing  alloy.  The  die  is  reinforced  by  the  addition 
of  a  brass  head.  A  flattened  pyramid  of  the  latter  metal,  having  a 
tinned  base  of  three  inches  or  more,  is  heated  until  the  solder  or  tin  is 
fused ;  upon  this  surface  the  base  of  the  die  is  set ;  when  the  surfaces 
are  united  cold  water  is  poured  over  die  and  counter. 

These  methods  are  rarely  practised,  as  moulding  in  sand  is  preferable 
for  obvious  reasons. 

1  A  similar  method  has  been  described  bv  Dr.  I.  N.  Broomell,  Internat.  Dent.  Joum., 
1890. 

^  Eichardson'  s  Mechanical  Dentistry,  3d  ed. 


CHAPTER    IX. 

SWAGED  METALLIC  PLATES. 

By  H.  H.  Burchard,  M.  T>.,  D.  D.  S. 


The  sheet  metals  employed  as  bases  of  support  for  artificial  teeth  are 
gold,  silver,  platinum,  and  aluminum. 

For  a  brief  period  sheet  palladium  was  applied  for  the  purpose.  A 
chance  overstocking  of  the  market  brought  the  commercial  value  of  the 
metal  to  a  price  making  it  economically  available  for  dental  use.  This, 
however,  was  but  a  curiosity  in  the  history  of  dentistry.  The  present 
pi-ice  of  the  metal  places  it  beyond  the  list  of  those  available  for  plates. 

Palladium  possesses  almost  the  infusibility  and  insolubility  of  platinum, 
and  has  the  additional  properties  of  greater  rigidity  and  a  less  specific 
gravity  to  recommend  it. 

Platinum  is  rarely  or  never  used  as  a  base-plate  for  soldered  den- 
tures ;  it  is  too  soft  and  inelastic  :  its  infusibility  fits  it  for  employment 
when  covered  by  substances  fusing  at  high  temperatures,  as  where  faced 
with  porcelain  continuous-gum  work. 

The  alloy  of  platinum  and  iridium,  known  as  iridio-platinura,  is  oc- 
casionally employed  in  the  making  of  plates,  the  addition  of  iridium 
producing  a  very  rigid  alloy. 

Under  exceptional  conditions  plates  may  be  made  of  the  alloy  of  gold 
and  platinum,  called  platinous  or  clasp  gold ;  this,  however,  is  rare  :  the 
alloy  is,  as  a  rule,  only  employed  for  clasps  and  to  form  supplementary 
pieces  for  strengthening  the  weak  areas  in  plates  made  of  more  pliable 
alloys.  It  is  employed  when  either  rigidity,  elasticity,  or  both,  are  re- 
quired. 

Aluminum  is  occasionally  employed  as  a  base-plate,  the  denture  proper 
being  mounted  in  vulcanite.  Its  lightness  and  comparatively  easy  work- 
ing properties  recommend  it,  its  greatest  deficiency  being  the  impractica- 
bility of  neatly  and  eifectively  soldering  it.  (See  chapter  on  Aluminum, 
page  146.)  The  metals  commonly  employed  are  gold  and  silver,  the  latter 
used  but  seldom  since  the  introduction  of  vulcanite. 

Sheet  gold  for  making  plates  is  usually  18  carats  fine  ;  it  should  never 
be  of  less  fineness,  and  if  finer  than  20  carats  does  not  possess  sufficient 
rigidity. 

Silver  plate  is  the  900-fine  alloy  known  as  coin  silver.  Pure  silv^er 
is  too  soft.  An  alloy  of  silver  and  platinum  is  to  be  preferred  to  the 
coin  silver  ;  it  is  more  rigid,  and  may  be  made  more  so  by  increasing  the 
percentage  of  platinum  in  the  alloy ;  it  is  less  liable  to  tarnish,  and  has 

.S19 


320  SWAGED  METALLIC  PLATES. 

a  much  better  surface.  It  is  much  less  rigid  than  platinous  gold.  (See 
Alloys  of  Silver,  page  120.) 

When  the  employment  of  a  metal  plate  is  an  imperative  indication, 
economical  reasons  alone  prompt  the  use  of  silver.  Gold  is  of  all  metals 
best  adapted  for  the  purpose ;  by  varying  the  fineness  of  the  alloy  and 
its  components  any  desired  quality  of  plate  may  be  obtained. 

Indications  for  the  Use  of  Metal  Plates. — Metal  plates  possess 
certain  advantages  over  those  of  vulcanite,  celluloid,  or  even  continuous 
gums,  which  are  utilized  when  and  where  indicated.  They  are  stronger, 
thinner,  smoother,  and  have  a  greater  conductivity  than  any  of  the  veg- 
etable bases. 

Mouths  in  which  it  has  been  shown  that  plates  constructed  of  vul- 
canite exercise  an  undesirable  influence,  owing  mainly  to  the  non-conduc- 
tivity keeping  the  underlying  structures  at  a  constant  temperature,  a 
metal  plate,  preferably  gold,  should  be  substituted. 

Metal  plates  are  an  imperative  indication  when  the  distance  between 
the  natural  gums  and  occluding  teeth  is  very  slight,  or  when  these  latter 
in  occlusion  touch  the  gum  of  the  antagonizing  arch.  The  attachment 
of  the  teeth  for  such  cases  must  necessarily  be  by  means  of  solder,  and  a 
very  thin  plate  is  alone  admissible  ;  so  that  vulcanite,  the  stronger  of  the 
vegetable  bases,  is  inadmissible. 

Peculiarities  of  the  Plate  Metals. — In  manipulating  gold  it  must 
be  frequently  annealed,  raising  it  to  a  dull  red  heat  and  plunging  it  into 
cold  water.  Under  manipulation  it  soon  becomes  very  elastic  and  obdu- 
rate, and  must  be  reannealed  as  soon  as  this  condition  is  re-established. 
20-carat  gold,  while  not  as  rigid  or  elastic  as  18-carat,  is  not  so  ho- 
mogeneous an  alloy  :  although  it  is  softer,  it  has  a  greater  tendency  to 
crack  under  manipulation,  and  much  care  must  be  exercised  in  working 
it  over  tuberosities  and  into  undercuts.  Gold  may  be  stretched — that  is, 
it  exhibits  its  malleability  under  the  operation  of  swaging — but,  as  this 
thins  the  ])late,  it  is  better  to  so  manipulate  the  latter  that  it  maintains  a 
uniform  thickness.  It  is  to  be  pressed  into  position,  not  turned  into  it, 
as  is  done  under  the  operation  of  spinning  or  raising  sheet  metal. 

Particles  of  base  metal  must  be  kept  from  its  surface  :  a  particle  of 
lead  will  form  with  the  gold  underlying  it  a  brittle  alloy,  melting  at  a  low 
temperature,  so  that  when  the  plate  is  heated  a  hole  is  burned  through 
the  plate  at  that  point. 

Heavy  sheets  of  gold,  as  indeed  of  any  metal,  work  more  smoothly 
and  exhibit  fewer  wrinkles  than  thin  sheets,  but  their  adaptation  is  not 
so  close.  The  latter  require  much  care  to  work  smoothly,  the  former 
much  force,  and  generally  a  zinc  counter-die  to  produce  accurate  adapta- 
tion to  the  die. 

Platinum  is  annealed  at  a  very  high  temperature,  and  then  becomes 
very  pliable,  and  offers  a  surface  to  which  the  base  metals  attach  them- 
selves closely  ;  and  as  some  of  these  latter  form  very  fusible  alloys,  pen- 
etrating the  substance  of  the  platinum  as  soon  as  heated  red,  care  must 
be  exercised  that  the  surface  of  the  platinum  be  kept  free  from  such 
contamination. 

Silver  is  annealed  at  a  temperature  a  little  below  red  heat :  its  surface 
oxidizes  quickly  above  that  point,  and  it  fuses  with  startling  suddenness. 
This  metal  almost  invariably  suffers  more  or  less  change  of  form  in  heat- 


FORMING   THE  PATTERN.  321 

ing.  Although  requiring  less  frequent  annealing  than  gold,  it  is  more 
liable  to  crack  unexpectedly. 

Aluminum  behaves  under  the  swaging  hammer  after  the  manner  of 
sheet  zinc.  If  annealed  at  too  high  a  temperature,  it  becomes  brittle  and 
cracks  readily ;  annealed  and  manipulated  deliberately  at  a  low  tempera- 
ture, it  is  tough  and  fibrous.  More  pressure  than  percussion  is  required 
to  adapt  it — the  reverse  of  the  platinoid  alloys,  which  require  hard  blows 
to  adapt  them. 

Palladium  is  at  present  never  used,  but  should  it  ever  become  cheap 
enough  for  dental  application,  it  is  to  be  worked  like  gold. 

Forming-  the  Pattern. — The  first  step  in  the  making  of  the  plate  is 
the  important  detail  of  forming  the  pattern.  Due  regard  for  economy 
suggests  that  the  pattern  be  no  larger  than  the  plate  itself — than  is  abso- 
lutely necessary.  Gold  plate  in  the  condition  of  scrap  has  its  commercial 
value  diminished  25  per  cent. 

The  pattern  should  be  formed  upon  the  die,  to  avoid  the  bruising  of 
the  plaster  model. 

A  sheet  of  pattern  foil  about  four  inches  square,  and  stout  enough 
to  require  some  force  in  manipulating  it,  is  laid  upon  the  die,  and  by  the 
fingers  is  pressed  into  the  deeper  portions  of  the  die  :  when  adaptation 
is  as  close  as  can  be  made  by  such  means  the  rubber  tip  of  a  lead  pencil 
is  used  to  secure  a  closer  adaptation ;  this  is  succeeded  by  the  pressure 
of  small  smooth  points  made  of  old  tooth-brush  handles  until  the  pattern 
metal  fits  the  die.  It  is  marked  by  a  sharp  steel  point  along  the  plate 
outline,  and  a  penknife  blade  applied  to  cut  off  tlie  surplus  metal.  Pat- 
terns for  partial  plates  should  be  cut  out  carefully  at  the  necks  of  the 
teeth. 

The  chamber-piece  should  also  be  represented  in  a  pattern,  extending 
on  all  sides  about  one-eighth  of  an  inch  from  the  base  of  the  chamber. 
Occasionally,  in  cases  having  an  unusual  distance  from  condyle  to  con- 
dyle, those  in  which  experience  demonstrates  that  lateral  bending  is  a 
danger,  the  chamber-piece  may  be  extended  at  the  angles,  forming  but- 
tresses to  the  plates  (see  Fig.  358). 

Ficx.  358.  Fig.  359. 


The  pattern  is  removed  from  the  die  and  carefully  flattened  between 
the  fingers.  It  is  then  laid  upon  a  sheet  of  cardboard,  and  an  outline 
about  one-eighth  of  an  inch  larger  than  the  tin  pattern  is  marked. 
Adepts  in  the  laboratory  require  less  margin,  novices  usually  more. 

21 


322  SWAGED  METALLIC  PLATES. 

At  places  representing  the  necks  of  teeth  the  plate  should  always  be 
cut  with  a  rounded,  never  an  angular,  outline.  Patterns  for  lower  plates 
require  additional  care  :  the  adaptation  of  the  tin  along  the  lingual  aspect 
must  be  very  accurate.  It  is  a  matter  of  some  difficulty  to  accurately 
straighten  or  flatten  these  patterns,  and  it  is  of  the  utmost  importance 
that  no  distortion  occur  in  the  operation.  The  true  outline  being  repre- 
sented by  the  solid  lines  (Fig.  359),  it  will  readily  be  seen  that  if  the 
pattern  were  bent  to  the  outlines  of  the  dotted  line,  a  plate  cut  by  such 
a  pattern  could  not  be  adapted  to  the  die  with  accuracy. 

A  greater  surplus  is  allowed  with  partial  lower  plates,  to  compensate 
for  the  greater  danger  of  the  displacement  of  the  laminae  in  swaging. 

For  upper  plates  the  patterns  are  duplicated  in  plates  of  No.  26  of 
the  B.  and  S.  gauge.  The  cap  piece  is  to  be  of  No.  28,  or,  under  excep- 
tional circumstances,  No.  27  ;  that  is,  where  an  increased  rigidity  of  the 
plate  is  demanded. 

Lower  plates  are  usually  made  of  two  laminae  of  No.  29.  In  partial 
lower  cases,  across  the  space  occupied  by  natural  teeth,  and  to  about 

one-half  an  inch  beyond  on  both 
Fig.  360.     ^  sides,  a  piece  of  platinous  gold 

No.  27  is  fitted  as  described  be- 
low :  without  this  supplementary 
piece  these  plates  bend  too  easily 
(Fig.  360). 

Plates  for  upper  dentures 
which  are  to  be  retained  by  means 
of  clasps  are  preferably  made  of 
two  laminae  of  No.  30  plate : 
their  horseshoe  form  is  an  ele- 
ment of  weakness,  and  a  single 
lamina  of  plate  when  sufficiently 
rigid  is  too  thick  to  be  accurately 
adapted  :   however,  through  the 

Partial  lower  plate,  withj^einforcing  piece  in  posi-      ^^^  ^f  ^  ^^ ^^^  COUUter-dic    a  plate 

of  No.  24  gauge  may  be  well 
adapted ;  and  this  is  the  thickness  to  be  employed  when  the  operator 
prefers  a  single  plate. 

The  same  care  is  exercised  in  flattening  these  patterns  as  for  partial 
lower  plates.  The  results  due  to  distortion  of  the  pattern  are  not  so  great 
as  with  the  lower  plates,  but  are  none  the  less  annoying,  and  it  may  be 
serious. 

Forming  the  Plates. — The  poorer  die  is  cleansed,  assuming  that  the 
plate  is  one  for  a  full  upper  denture,  by  brushing  off  any  particles  of  sand 
or  metal.  The  plate  is  laid  upon  a  block  of  charcoal,  and  the  broad  flame 
of  the  blowpipe  directed  against  it  until  it  is  a  dull  red  :  it  is  then 
plunged  into  water.  The  coating  of  oxide  formed  by  this  heating  is  per- 
mitted to  remain,  as  it  serves  to  prevent,  in  some  measure,  the  intimate 
contact  of  the  surface  of  the  gold  with  the  base  metal  of  the  die  and 
counter-die.  The  tin  pattern  is  laid  upon  the  annealed  plate,  and  its  out- 
line marked  with  a  sharp  point.  The  points  of  the  pattern  representing 
the  anterior  and  posterior  of  the  middle  line  of  the  vault  are  marked  on 
the  plate,  which  is  then  bent  by  the  fingers  along  a  line  having  these 


FORMING  THE  PLATES.  323 

points  as  extremities.  It  is  then  placed  upon  the  die,  its  posterior  edge 
carefully  placed  in  position,  and  by  means  of  blows  delivered  with  the 
horn  mallet  the  posterior  part  of  the  plate  is  driven  into  position  :  from 
this  work  forward,  first  along  the  median  line,  driving  the  plate  into  con- 
tact with  the  die  at  the  deepest  portions  of  the  latter.  As  soon  as  the 
metal  plate  develops  an  increased  elasticity,  remove  from  the  die,  brush 

Fig.  361. 


Horn  swaging  mallet. 

it  free  of  any  adherent  particles  of  metal,  and  reanneal  it ;  then  place  on 
the  die,  and  continue  the  malleting  until  a  rough  adaptation  of  the  plate 
to  the  vault  is  .secured.  If  the  partial  counter-dies  have  been  made,  the 
first  of  these  is  placed  over  the  plate  and  struck  three  or  four  times  with 
the  heavy  swaging  hammer.  Brush  and  reanneal  the  plate ;  then,  using 
the  next  counter-die,  swage  again.  Now,  while  the  palatal  portion  of 
the  plate  is  held  in  position  by  the  partial  counter-die,  the  broad  end  of 
the  horn  mallet  (Fig.  361)  is  employed  to  roughly  form  the  alveolar  por- 
tion of  the  plate. 

The  outer  edge  of  the  plate  at  this  stage  having  a  greater  length  than 
the  plate  outline  marked  along  the  model,  it  is  evident  that  to  adapt  one 
to  the  other  at  least  a  portion  of  the  surplus  length  must  be  cut  out,  or  the 
plate  must  be  so  manipulated  as  to  contract  it  along  this  line,  or  else  the 
amount  of  surplus  length  will  be  represented  by  wrinkles  in  the  plate. 
Some  operators  prefer  removing  from  the  portion  of  the  plate  at  the 
frsenum  labialis  a  V-shaped  section  something  less  than  enough  to  fully 
compensate  for  the  increased  length  of  the  plate  line.  The  writer  prefers 
a  method  of  manipulation  which  does  not  involve  cutting  the  plate.  It 
is  difficult  and  somewhat  tedious  to  prevent  wrinkling  by  this  method, 
but  through  the  exercise  of  care,  plates  may  be  adapted  to  even  marked 
alveolar  under-cuts  without  wrinlding. 

The  plate  is  cut  something  larger  than  usual  along  this  portion  of  its 
outline.  When  it  has  been  adapted  to  the  stage,  and  through  the  means 
described  it  is  well  annealed  and  placed   in  the  counter-die,  the  die  is 


324  SWAGED  METALLIC  PLATES. 

set  in  it,  and  one  or  two  light  blows  are  delivered  with  the  swaging  ham- 
mer on  the  die.  The  plate  is  again  annealed  ;  any  wrinkles  which  have 
formed  are  removed  by  blows  of  the  horn  mallet ;  set  in  the  counter-die, 
and  again  swaged  lightly.  Repeat  the  annealing,  malleting,  and  swaging 
until  all  the  wrinkles  along  the  plate  edge  are  but  small  irregularities 
and  nowhere  extend  to  the  final  plate  outline.  It  is  then  annealed  and 
swaged,  using  now  heavy  blows  on  the  die,  and  turning  the  latter  with 
the  left  hand,  so  that  the  blows  are  delivered  above  successive  portions 
of  the  plate.  The  edge  of  the  plate  is  now  trimmed  to  near  its  true 
line. 

Forming"  the  Cap. — The  cap  piece  is  annealed  and  placed  in  position 
in  the  die,  and  fixed  there  by  light  malleting.  The  first  of  the  partial 
counter-die  is  placed  over  it  and  swaged.  The  gold  is  annealed  and 
swaged  by  the  best  counter-die.  A  pair  of  dividers,  measuring  the  nar- 
rowest portion  of  the  ledge  of  the  cap,  is  passed  around  the  chamber- 
piece,  marking  a  ledge  of  uniform  width  ;  it  is  then  trimmed  along  this 
outline,  and  finally  its  edge  is  given  a  long  bevel  from  its  upper  surface. 

Plate  and  cap  are  again  annealed ;  the  latter  set  in  the  second  or 
finishing  counter-die,  and  swaged.  Removing  the  cap,  the  plate  itself  is 
placed  in  the  counter-die,  and  it  is  again  swaged. 

Cutting  Out  the  Chamber. — Midway  between  the  lines  representing 
the  top  and  base  of  the  vacuum  chamber  the  plate  is  pierced  by  a  plate 
punch.  In  this  opening  the  blade  of  a  plate  saw,  set  to  draw,  not  push 
cut,  is  placed,  and  then  securely  fastened  in  its  frame.  Rubbing  the 
saw-blade  with  wax  to  make  it  cut  more  smoothly,  the  chamber  is  sawn 
out  along  a  line  a  trifle  above  the  base-line.  The  plate  is  now  swaged, 
and  then  placed  on  the  plaster  model.  The  chamber  outline  is  filed  out, 
using  a  small  smooth-cut  half-round  file  for  the  purpose,  until  the  line 
of  junction  between  the  base  of  the  wax  chamber  and  the  model  is  just 
visible . 

The  cap  piece  and  plate  are  again  annealed,  the  former  placed  in 
position  in  the  counter-die,  and  over  it  the  plate,  the  die  set  over  them, 
and  then  by  several  hard  blows  the  swaging  is  completed.  By  means 
of  sharp  shears,  using  only  their  tips,  the  plate  is  trimmed  to  almost  the 
outline  marked  on  the  model,  and  then  a  smooth  file  is  used  to  complete 
the  shaping ;  next  an  annealing,  and  then  final  swaging. 

Testing  the  Adaptation. — The  plate  and  cap  are  boiled  in  a  1:10 
sulphuric-acid  solution,  washed,  dried,  and  the  plate  tried  on  the  model. 
The  adaptation  is  tested  by  noting  that  the  plate  is  in  contact  with  the 
model  throughout  its  upper  edge,  and  that  the  edge  of  the  chamber  is  in 
contact  with  the  model.  If  zinc  dies  have  been  used,  the  posterior  edge 
of  the  plate  will  be  about  one-sixteenth  of  an  inch  short  of  contact  with 
the  vault.  If  a  Babbitt-metal  finishing  die  have  been  used,  this  portion 
of  the  plate  should  be  in  contact  with  the  vault.  The  uniformity  of  the 
contact  is  tested  by  pressure  applied  along  the  height  of  the  ridge. 
Pressure  at  any  point  should  not  cause  movement  of  the  plate  on  the 
model.  Next  apply  alternating  pressure  on  the  sides  ;  if  the  adaptation 
be  correct,  there  should  be  no  rocking.  Should  the  plate  rock,  the  point 
upon  which  it  appears  to  ride  is  noted.  The  cause  of  the  fault,  as  a  rule, 
will  be  found  in  the  die,  usually  due  to  some  prominence  being  bruised 
during  the  swaging,  or  it  may  be  an  inaccuracy  due  to  imperfect  mould- 


ATTACHING    THE  CHAMBER-PIECE. 


325 


Fig.  362. 


ing.  The  plate  is  annealed :  a  thickness  of  pattern  tin  is  placed  over 
the  faulty  spot  of  the  die,  and  the  counter-die  scraped  out  at  the  corre- 
sponding place.  The  plate  is  set  in  position  on  the  die  and  swaged, 
then  placed  on  the  model,  and.  again  tested. 

Should  it  be  impossible  to  secure  freedom  from  rock  by  this  means, 
it  is  advisable  to  made  a  new  die  and  counter-die,  exercising  the  utmost 
care  in  moulding. 

Attaching-  the  Chamber-piece. — When  the  plate  fits  the  model  cor- 
rectly the  chamber-piece  is  set  upon  the  former,  and  it  is  noted  whether 
it  is  in  perfect  contact  with  the  plate.  The  contact  surfaces  are  cleansed 
by  boiling  in  the  sulphuric-acid  solution,  and  then  by  scraping  until  they 
are  bright.  Borax  is  applied  to  the  prepared  surface,  and  the  cap  is  clamped 
to  the  plate  by  means  of  two  clamps  made  of  No.  16  iron  wire,  shown  in 
Fig.  362 — one  applied  to  either  side  of  the  chamber-piece  flange,  the  other 
arms  pressing  the  palatal  surface  of  the  plate.  A  small  square  of  18-carat 
solder  is  placed  at  the  forward  extremity 
of  the  chamber-piece,  and  the  plate  set 
upon  a  bed  made  of  pieces  of  charcoal  so 
distributed  as  to  furnish  a  support  to  the 
entire  plate.  The  broad  flame  of  a  blow- 
pipe is  rapidly  passed  around,  beneath, 
and  over  the  plate  until  the  latter  is  heated 
to  a  cherry  red,  when  a  fine  flame  is 
directed  against  the  plate  near  the  solder 
until  the  latter  begins  to  fuse,  when  the 
flame  is  thrown  on  the  flange  of  the 
chamber-piece  and  the  molten  solder 
drawn  beneath  it.  When  the  piece  is 
cool,  note  whether  the  contact  of  the  cap 
piece  and  the  plate  is  perfect;  if  there 
be  any  separation — and  separation  of  the 
surfaces  is  not  unusual — the  plate  is 
reswaged.  With  the  clamps  in  position  four  squares  of  solder  are  placed 
along  the  sides  of  the  cap  and  one  at  its  posterior  edge,  the  plate  heated, 
and  the  solder  melted  as  the  first  piece ;  the  fine  flame  is  then  passed 
rapidly  around  the  chamber-piece  until  the  solder  flows  freely,  and  upon 
examination  is  seen  to  fill  the  joint  line  at  the  palatal  aspect  of  the  plate. 
If  the  operation  have  been  carefully  done,  the  plate  will  have  suflered  no 
change  of  form,  but  should  this  latter  have  occurred  reswaging  is  necessary. 

The  plate  is  boiled  in  the  acid  solution,  washed,  and  dried.  The 
edges  are  smoothed  and  rounded  with  No.  0  emery-paper,  and  its  surfaces 
brightened  with  brush  wheels  and  powdered  pumice.  It  is  now  ready 
for  trial  in  the  mouth. 

Swaging-  Rimmed  Plates. — If  the  plate  is  to  have  its  upper  edge 
turned  over  to  form  a  rim,  the  model  has  been  prepared  and  dies  made 
as  described  in  Chapter  X. 

Additional  care  is  necessary  in  manipulating  the  metal  over  the  ridge 
in  such  plates.  The  annealing  and  light  swaging  are  to  be  more  frequent. 
After  a  moderately  good  adaptation  is  had,  the  plate  is  placed  on  the  die, 
and  by  means  of  a  brass  chaser  having  a  sharp  wedge-shaped  end  about 
a  quarter  of  an  inch  broad,  the  angle  of  the  rim  is  clearly  outlined,  driving 


326  SWAGED  METALLIC  PLATES. 

the  plate  along  this  line  into  the  angle  by  rapidly-delivered  blows  of  a 
small,  light  hammer. 

When  swaging  on  the  finishing  die  the  plate  is  covered  by  a  sheet  of 
the  cloth  in  which  dental  rubbers  are  enclosed.  The  cloth  is  wetted  and 
laid  over  the  plate,  then  covered  by  the  counter-die  and  swaged.  With- 
out this  adjunct  it  is  frequently  difficult  to  withdraw  the  plate  from  the 
counter-die  without  bending  it.  The  same  device  is  useful  in  swaging  all 
plates  which  cling  obstinately  to  the  counter-die. 

The  plate  edge  is  trimmed  to  the  correct  outline  and  smoothed. 

Plates  Without  the  Cut-out  Chamber. — Plates  are  seldom  made 
without  the  cut-out  chamber  unless  designed  as  a  basis  for  continuous- 
gum  work  or  made  of  aluminum,  for  which  there  is  no  suitable  solder. 

It  is  a  difficult  but  necessary  task  to  so  adapt  the  edges  of  the  vacuum 
chamber  that  they  shall  fit  perfectly  to  prevent  the  access  of  air  to  the 
chamber  space.  The  plate  is  annealed  frequently,  and  for  the  final 
swaging  a  zinc  counter-die  is  advisable  to  drive  the  edge  of  the  chamber 
into  position.  If  this  does  not  produce  a  sharp  and  distinct  outline,  a 
small  brass  chaser,  driven  by  rapidly  repeated  blows  of  a  small  hammer, 
is  employed  to  define  the  chamber  edge.  This  is  succeeded  by  a  swaging 
with  the  zinc  counter-die.  Be  careful  that  the  edge  of  the  chaser  does  not 
perforate  the  plate,  and  at  the  completion  of  the  swaging  examine  the  plate 
at  the  chamber  edge  for  minute  openings  :  should  there  be  any,  they  are 
to  be  covered  by  a  small  piece  of  thin  plate  attached  by  means  of  solder. 

In  the  making  of  swaged  plates  of  aluminum  select  plate  of  about 
No.  24  gauge.  In  being  reduced  to  plate  from  the  ingot  this  metal  ap- 
pears to  acquire  its  maximum  toughness  at  this  thickness  ;  that  is,  as  far 
as  the  swaging  operation  is  concerned.  Anneal  the  metal  at  as  low  a 
heat  as  possible — considerably  below  red  heat.  The  finished  plate  is 
tougher  if,  instead  of  plunging  it  into  cold  water  after  heating,  it  be 
allowed  to  cool  gradually.  Covering  its  surface  with  oil  and  burning 
the  latter  off  anneals  the  plate,  and  at  a  safe  temperature,  but  a  dirty 
discoloration  difficult  to  remove  remains.  Over  the  face  of  the  die  spread 
a  layer  of  tissue-paper  and  press  the  counter-die  down  upon  it.  Over  the 
tissue-paper  then  set  the  annealed  plate  and  press  into  the  deeper  portions 
of  the  vault.  In  working  this  metal  it  is  preferable  to  have  a  series  of 
partial  counter-dies.  The  smallest  of  these  is  covered  by  a  wet  sheet  of 
rubber  muslin,  and  the  plate  is  lightly  swaged.  It  is  reannealed  and 
placed  on  the  die,  covered  by  the  next  sized  counter-die,  and  again  swaged. 
It  is  advisable  to  always  have  interposed  between  the  plate  surfaces  and 
those  of  the  die  and  counter-die  enclosing  it  two  layers — one  of  paper  next 
to  the  die,  another  of  muslin  next  to  the  counter-die — to  prevent  con- 
tamination of  its  surface  by  the  base  metals.  The  entire  process  of 
swaging  should  be  gentle  and  gradual.  The  metal  is  very  pliable  and 
readily  adapted ;  but,  any  sudden  force  tends  to  fracture  it.  An- 
nealed at  too  high  a  temperature,  it  develops  an  increased  liability  to 
fracture.  In  giving  the  final  finish  to  this  metal  use  dry  brushes ;  the 
wet  polishing  powders  form  upon  its  surface  a  black  and  tenacious  scum. 

Partial  Plates. — Plates  for  partial  dentures  are  of  three  varieties : 
first,  those  for  the  lower  jaw ;  second,  the  tM^o  types  used  for  the  upper 
jaw,  those  retained  by  means  of  a  vacuum  chamber ;  and,  third,  those 
held  in  position  by  means  of  clasps  attached  to  the  natural  teeth. 


PARTIAL  PLATES. 


327 


The  first  and  last  of  these  require  special  description  by  themselves. 
Partial  upper  plates,  having  vacuum  chambers,  are  made  after  the  same 
principle  as  any  upper  plate.     The  dies  are  made  and  prepared  as  de- 
scribed in  the  foregoing  chapter.     The  tin 
pattern  is  to  be  made  so  that  it  represents  Fig.  363. 

an  accurate  copy  of  the  future  plate. 

When  flattened  a  duplicate  is  made  of 
18-carat  gold  plate  of  No.  26  gauge,  and 
made  about  one-sixteenth  of  an  inch  or 
more  larger,  and  giving  a  rounded  outline 
to  the  portions  about  the  necks  of  the 
teeth  (Fig.  363). 

When  the  plate  has  been  annealed  the 
tin  pattern  is  laid  on  it  and  its  outlines 
plainly  marked.  These  lines  serve  as  a 
guide  in  swaging,  by  keeping  them  oppo- 
site to  and  against  the  respective  teeth. 

The  median  line  is  noted  as  with  the 
full  j51ate ;  the  gold,  well  annealed,  is  laid  upon  the  die,  from  which  the 
teeth  have  been  cut,  and  malleted  until  the  median  line  is  represented  in 
its  proper  position  in  the  plate.  The  malleting  is  continued,  alternating 
from  side  to  side,  until  the  gold  becomes  elastic ;  it  is  then  reannealed 
and  the  malleting  resumed. 

Before  any  attempt  at  swaging  proper  is  made  the  plate  should  be 
sufficiently.,  adapted  by  the  mallet  to  secure  it  against  slipping  from 
position.      When  this  degree  of  t?         a 

adaptation  is  had,  the  plate  is  an-  ^^' 

nealed  and  set  in  proper  position 
in  the  counter-die,  the  die  placed 
over  it,  and  a  few  very  light  blows 
are  struck.  The  die  and  counter 
are  separated  for  assurance  that 
the  plate  is  in  position.  If  it 
is  not,  or  the  plate  is  found  to 
have  moved,  it  is  reannealed 
and  further  malleted,  and  again 
placed  in  the  counter-die.  When 
it  is  certain  that  it  will  not 
slip  several  heavy  blows  are 
struck  with  the  swaging  hammer, 
driving  the  plate  well  into  posi- 
tion. It  is  removed  from  the  die 
and  boiled  in  pickle,  then  rean- 
nealed. A  sharp  point  is  passed 
around  the  plate,  marking  it 
plainly  about  one-sixteenth  of  an 
inch  beyond  the  final  line  of 
the  plate.  By  means  of  sharp- 
pointed  shears,  cutting  with  their  points  alone,  by  plate-nippers 
(Fig.  364),  removing  small  portions  at  a  time,  and  finally  by 
half-round   plate   files,  the  plate   is   dressed  out  to  the   lines  marked, 


Plate  nippers,  three  sizes. 


328  SWAGED  METALLIC  PLATES. 

and  no  more.  It  is  again  placed  in  the  counter-die  and  swaged 
heavily. 

If  the  case  be  one  having  very  deep  and  angular  rugse  or  a  very 
deep  vault,  it  is  occasionally  necessary  to  employ  a  zinc  counter-die  to 
drive  the  metal  into  the  deepest  parts. 

The  chamber  is  cut  out  as  before  described,  the  cap  piece  swaged,  and 
next  the  plate  and  cap  are  swaged  together,  and  the  amount  of  trimming 
necessary  to  bring  the  edges  of  the  plate  to  the  outline  marked  on  the 
model  is  noted.  The  surplus  metal  is  to  be  removed  by  means  of  small 
half-round  plate  files  of  the  finer  cuts.  The  pieces  are  annealed  and 
transferred  to  the  finishing  die,  and  swaged  separately  at  first,  and  then 
together.  After  boiling  in  the  sulphuric-acid  solution,  the  plate  is  tried 
on  the  model.  All  of  its  edges  should  be  in  contact  with  the  model,  and 
correspond  with  the  pencilled  outline.  It  should  respond  to  the  same 
test  as  for  any  plate — immobility  when  any  part  is  pressed  upon.  The 
chamber-piece  is  soldered  in  as  described. 

Strengthening-  Pieces. — If  the  case  be  one  having  an  unusual  dis- 
tance between  its  posterior  extremities,  and  which  exhibits  an  undue 
weakness  laterally,  it  is  advisable  to  furnish  additional  support  across 
these  parts  of  the  plate.  The  pattern  for  the  chamber-piece  has  its  basal 
angles  continued  to  the  posterior  angles  of  the  plate  (see  Fig.  358),  and 
the  pattern,  uniformly  enlarged,  is  duplicated  in  gold.  Additional  care 
is  necessary  in  the  first  swaging  of  this  piece  that  it  should  not  alter 
position.  It  is  fitted,  trimmed,  and  bevelled  as  any  chamber-piece,  and 
then  soldered  in  position. 

Should  the  case  exhibit  breaks  in  its  continuity  which  permit  its  ready 
bending,  additional  supports  are  required.  Around  isolated  teeth  crescents 
of  plate  No.  27  gauge  about  a  quarter  of  an  inch  broad  are  swaged.  The 
writer  usually  places  these  pieces  upon  the  palatal  surface  of  the  plate, 
filing  them  to  a  feather  edge  before  attaching  them.  Occasionally  it  is 
necessary,  with  plates  bearing  alone  the  posterior  teeth,  to  place  across 
the  anterior  weak  segment,  opposite  the  natural  teeth,  a  stiffening  piece. 
This  is  to  be  made  of  No.  29  plate ;  it  is  annealed,  roughly  swaged,  and 
cut  to  a  uniform  width  of  about  three-eighths  of  an  inch  or  less.  The 
plate  and  piece  are  cleansed  and  the  posterior  edge  of  the  latter  bevelled. 
A  cream  of  borax  is  applied  to  the  surfaces  to  be  united,  a  minute  piece 
of  solder  placed  at  a  point  of  the  anterior  edge ;  then,  heating  first  the 
body  of  the  plate  under  the  blowpipe,  the  solder  is  fused,  and  serves  to 
hold  the  pieces  in  correct  position.  Transferred  to  the  die,  the  two  are 
well  swaged.  The  extremities  of  the  piece  are  held  against  the  plate  by 
means  of  two  small  clamps,  two  small  squares  of  solder  placed  at  the 
anterior  edge,  and  the  plate  is  heated  until  the  solder  flows  between  plate 
and  teeth,  filling  the  space  perfectly  ;  more  solder  is  added  if  necessary, 
but  never  use  an  excess.  The  plate  is  now  trimmed  about  the  necks  of 
the  teeth,  bevelling  from  the  lingual  side. 

A  neat  finish  is  given  about  natural  teeth  and  an  effective  strength- 
ening piece  furnished  by  partially  encircling  them  with  a  piece  of  No. 
16  gold  wire  which  has  been  fitted  and  then  flattened  ;  this  is  attached 
to  the  plate  by  means  of  the  minimum  of  solder. 

At  the  sites  of  missing  teeth  the  rounded  tongues  of  plate  upon  which 
the  artificial  teeth  are  to  rest  are  cut  away,  so  that  when  the  artificial 


LOWER  PLATES. 


329 


teeth  are  adjusted  they  shall  hide  the  plate  perfectly,  and  yet  the  tongues 
furnish  adequate  basal  support.  The  edges  of  these  tongues  are  to  be 
given  a  long  bevel.  The  other  edges  of  the  plate  are  to  be  rounded 
and  smoothed. 

Lower  Plates. — Plates  for  lower  dentures  are  preferably  made  of 
two  laminae  of  metal,  using  for  the  purpose  No.  29.  If  made  of  a  single 
piece,  No.  24  gauge  is  to  be  employed.  Much  care  is  required  in  making 
and  flattening  the  patterns  for  these  plates,  as  any  carelessness  in  these 
operations  might  alter  the  width  or  distance  across  the  plate  extremities, 
thus  making  accurate  adaptation  of  the  plate  most  difficult  or  impos- 
sible. 

The  plates  are  annealed  :  one  is  taken  and  pressed  to  the  summit  of 
the  die  by  means  of  the  fingers ;  the  malleting  is  then  begun  at  the  mid- 
dle of  the  labial  aspect,  continuing  the  malleting  along  the  labial  and 
buccal  portions  until  there  is  a  rough  adaptation  of  this  portion.  Next 
mallet  the  lingual  aspect  until  it  assumes  an  approximately  correct  form, 
annealing  as  soon  or  as  often  as  the  piece  develops  elasticity.  When 
malleted  sufficiently  to  maintain  its  position  on  the  die,  it  is  transferred 
to  the  counter-die  and  swaged  lightly ;  when  assured  that  it  will  not 
slip  from  position  in  the  counter-die,  it  is  aimealed  and  swaged  well. 
The  process  is  to  be  repeated  with  plate  No.  2. 

Both  plates  are  now  annealed  and  swaged  together.  One  of  the 
pieces  is  trimmed  to  almost  the  plate  outline  marked  on  the  model,  the 
other  remaining  untrimmed,  forming  a  ledge  between  the  plates  which 


Fig.  365. 


Fig.  366. 


serves  to  hold  the  pieces  of  solder  which  are  to  unite  the  two.  The 
plates  are  again  annealed,  and  are  separately  swaged  on  the  Babbitt- 
metal  finishing  die,  and  next  swaged  together,  the  untrimmed  plate 
next  to  the  die. 


330  SWAGED  METALLIC  PLATES. 

This  latter  piece  is  boiled  in  the  sulphuric-acid  solution  and  placed 
on  the  model.  It  should  rest  firmly  upon  the  latter,  exhibiting  no 
movement  when  pressure  is  made  upon  any  point  of  the  plate.  Should 
the  alveolar  ridge  be  unusually  high,  it  is  a  useful  expedient  to  roughly 
shape  the  plate  along  the  groove  by  means  of  a  tooth-brush  handle  used 
as  a  chaser,  driving  the  middle  line  of  the  plate  into  a  concave  form,  a 
grooved  block  of  hard  wood  forming  the  piece  into  which  the  plate  is 
driven.  Plate-benders  occasionally  serve  a  useful  purpose  to  the  same 
end  (Fig.  365). 

When  the  larger  plate  fits  the  model  perfectly,  and  the  second  plate 
is  so  closely  adapted  to  the  first  that  their  point  of  union  is  almost  imper- 
ceptible, they  are  in  a  condition  to  be  soldered  together.  Both  are  boiled 
in  the  acid  solution,  and  the  surfaces  to  be  united  are  well  brushed  and 
brightened  by  means  of  a  coarse  brush-wheel  and  pumice  ;  they  are 
washed,  dried,  and  a  coating  of  borax  given  the  brightened  surfaces.  At 
the  middle  line,  and  on  either  side  near  the  posterior  extremities,  wrap- 
pings of  fine  binding  wire  are  placed,  holding  the  plates  firmly  together 
(Fig.  366).  Along  the  lingual  border  of  the  ledge  squares  of  solder  of 
the  same  fineness  as  the  plates  are  placed,  forming  a  continuous  line  of 
the  pieces :  no  solder  is  placed  on  the  labial  and  buccal  portions  of  the 
ledge.  The  solder  is  to  be  drawn  through  from  the  lingual  side,  so  as  to 
furnish  assurance  of  perfect  union  of  the  plates  throughout. 

The  plate  is  laid  on  a  bed  made  of  small  pieces  of  charcoal,  and  a 
blowpipe  flame  passed  above  it,  not  on  it,  until  efflorescence  of  the  borax 
ceases,  when  the  broad  flame  is  applied  to  the  plate  until  it  is  heated  to 
a  uniform  red,  when  the  fine  flame  is  directed  against  the  solder  pieces, 
fusing  them  one  by  one.  As  soon  as  the  pieces  have  melted,  a  larger 
flame  is  thrown  upon  the  labial  and  buccal  aspects  of  the  plate  until 
these  portions  are  at  a  higher  temperature  than  the  lingual  ledge,  the 
heat  carried  then  forward  until  the  entire  mass  of  solder  is  seen  to  flow 
like  water  and  appear  at  the  labial  and  buccal  portions  of  the  joint, 
uniting  the  plates  perfectly.  When  cold  the  binding  wires  are  removed 
and  the  plate  boiled  in  the  acid  solution.  The  ledge  of  the  lower  plate 
is  trimmed  away,  using  for  this  purpose  the  points  of  a  very  sharp  pair 
of  curved  shears  (Fig.  367).     The  trimming  is  completed  by  means  of 

Fig.  367. 


S.  S.  W.  curved  plate-shears. 

files,  and  when  the  plate  outline  corresponds  with  the  pencil  line  on  the 
model,  its  edges  are  rounded  and  smoothed  with  fine  emery-paper. 

Partial  Lo^wer  Plates. — The  most  difficult  class  of  plates  to  fit  accu- 
rately and  correctly  are  those  for  partial  lower  dentures.  The  operator's 
ingenuity  and  manipulative  ability  are  taxed  to  provide  in  such  cases 
acceptable  substitutes  for  the  lost  organs  :  however,  when  these  dentures 
are  well  made  and  adjusted  they  are  among  the  most  satisfactory  of 
prosthetic  appliances. 


PARTIAL  LOWER  PLATES. 


331 


Except  under  very  unusual  circumstances,  it  is  unwise  to  insert  a 
lower  piece,  when  no  teeth  but  the  second  and  third  molars  have  been 
lost,  the  increased  masticating  surface  thus  provided  rarely  compensates 
for  the  inconvenience  caused  by  the  presence  of  a  large  plate. 

Viewed  as  to  the  laboratory  operation  required  in  making  the 
plates,  the  cases  may  be  divided  into  two  classes  :  First,  those  in  which 


Fig.  368. 


Partial  lower  plate,  Class  1. 

the  natural  teeth  present  are  in  one  unbroken  column  ;  second,  those  in 
which  the  natural  teeth  are  in  broken  column. 

A  typical  case  of  the  first  class  is  most  common  of  all,  requiring  a 
partial  lower  denture,  six,  eight,  or  ten  of  the  anterior  teeth  remaining 
(Fig.  368). 

Fig.  369. 


Partial  lower  plate,  Class 


The  second  is  represented  by  cases  having  the  cuspids  and  bicuspids  of 
both  sides  remaining;  the  incisors  and  molars  are  to  be  replaced  (Fig.  369). 


332  SWAGED  METALLIC  PLATES. 

The  first  requisite  to  success  with  this  class  of  dentures  is  an  accurate 
impression,  always  to  be  taken  in  plaster.  In  the  degree  that  impression 
is  difficult  to  secure  by  the  use  of  plaster,  the  more  imperative  is  the  in- 
dication for  the  employment  of  that  material. 

The  plaster  model  should  have  strengthening  and  guiding  pins  in  all 
of  its  teeth  ;  the  base  should  be  broad  and  be  given  sloping  walls. 

Greater  stability  is  secured  by  making  these  plates  as  large  as  possible 
compatible  with  the  comfort  of  the  wearer.     The  plate  outline  is  marked 

at  its  lingual  borders  as  deep  as  possible,  with- 
out any  impingement  upon  the  tissues  movable 
by  the  movements  of  the  tongue,  and  to  rest 
upon  about  one-half  the  lingual  walls  of  the 
natural  teeth.  The  labial  and  buccal  edges 
are  carried  to  a  depth  which  shall  aiFord  a 
generous  support  to  the  artificial  teeth,  and  be 
clear  of  impingement  upon  the  soft  tissue  re- 
flected from  the  cheek  and  lip. 

To  neutralize  the  tendency  of  these  plates 
to  bury  the  external  border  in  the  soft  tissues 
their  edge  is  to  be  elevated  from  one-sixteenth 
of  an  inch  to  one-eighth  of  an  inch  by  placing  a  layer  of  wax  of  this 
thickness  over  that  portion  of  the  model.     (See  Chapter  VIII.) 

The  dies  and  counter-dies  are  made  as  described  in  Chapter  VIII.  The 
finishing  die  is  to  be  made  of  Babbitt  metal,  and  is  to  be  very  heavy. 

From  the  inferior  die  the  zinc  teeth  are  cut  a  trifle  above  the  plate 
outline,  and  the  angle  between  the  lingual  wall  and  tops  of  the  teeth 
made  acute,  so  that  by  bending  the  plate  over  the  edges  it  is  prevented 
from  slipping  during  the  operation  of  swaging. 

The  teeth  to  be  clasped  are  cut  almost  level  with  their  necks. 
The  plate,  to  assure  accurate  adaptation  and  to  increase  its  rigidity, 
should  be  made  of  two  laminae,  of  No.  29  gauge.  The  completed  piece 
should  have  sufficient  rigidity  to  resist  bending  even  when  severely  tried, 
so  that  an  additional  layer  of  material  is  necessary  across  the  weak  spaces, 
the  lingual  portions  of  the  plate,  which  are  back  of  the  natural  teeth. 
To  ensure  the  required  rigidity  this  supplementary  piece  is  to  be  made  of 
platinous  gold  of  No.  27  gauge.  A  greater  stiffness  and  better  aesthetic 
effect  are  given  if  this  piece  be  placed  between,  and  not  over,  the  two 
plates. 

Much  of  the  accuracy  of  the  fit  of  the  plate  will  depend  upon  the 
care  with  which  the  patterns  are  made.  Heavy  pattern  material  is  used 
for  this  purpose,  and  adapted  to  the  Babbitt-metal  die  so  that  it  is  an 
accurate  representation  of  the  future  plate.  Much  care  is  necessary  in 
flattening  it,  and  the  proper  pattern  is  cut  with  greater  surplus  than  usual 
with  other  classes  of  plates. 

The  pattern  for  the  supplementary  piece  extends  across  all  breaks  in 
the  plate  continuity  for  about  three-eighths  of  an  inch  beyond  on  both 
sides.  It  should  be  wide  enough  to  extend  from  the  necks  of  the  natural 
teeth  to  the  extreme  lower  edge  of  the  plate. 

Making-  the  Plate. — The  pieces  are  well  annealed,  and  one  is  taken 
and  bent  roughly  with  the  fingers.  It  is  malleted  into  approximate 
adaptation  at  the  middle  of  its  lingual  portion.     Next  the  buccal  sides 


MAKING   THE  PLATE.  333 

are  malleted,  and  as  soon  as  the  plate  becomes  obdurate  or  exhibits  a 
tendency  to  wrinkling  it  is  reannealed  and  again  malleted,  the  upper 
edge  of  the  plate  being  bent  over  the  cut  surface  of  the  zinc  teeth.  When 
it  is  approximately  fitted  by  this  means,  and  not  before,  the  plate  is 
placed  in  the  counter-die,  the  die  set  over  it,  and  tapped  gently  until  it 
begins  to  settle  into  position.  The  die  and  counter  are  separated,  and  if 
the  plate  maintains  its  position,  the  die  is  replaced  over  it  and  a  few 
moderately  heavy  blows  struck  with  the  swaging  hammer. 

Piece  No.  2  is  annealed  and  similarly  manipulated.  Both  pieces  are 
now  boiled  in  the  acid  solution  to  remove  the  particles  of  base  metal 
always  adherent,  and  again  annealed.  Each  in  turn  is  placed  between 
die  and  counter-die  and  swaged  well.  Usually  it  will  be  found  that  one 
piece  has  a  greater  surplus  at  its  lingual  border  than  the  other,  and  it  is 
set  aside.  The  other  plate  is  trimmed  by  means  of  sharp  shears,  plate- 
nippers,  and  files  until  it  is  within  a  trifling  distance  of  the  plate  outlines 
marked  on  the  model. 

The  supplementary  piece  of  platinous  gold  is  annealed  at  a  high  heat, 
and  malleted  to  the  die,  reannealed  and  remalleted.  It  is  next  placed  in 
position  in  the  counter-die  and  swaged,  again  annealed,  and  again  swaged. 
The  extreme  elasticity  of  this  alloy  necessitates  that  it  should  be  annealed 
more  frequently  than  ordinary  plate.  It  is  then  trimmed  to  its  proper 
size,  and  all  of  its  edges  except  the  inferior  border  bevelled.  All  of  the 
pieces  are  annealed ;  the  trimmed  plate  is  set  in  the  counter-die :  within 
it  is  placed  the  stiifening  strip,  and  over  both  the  untrimmed  plate,  the 
die  placed  in  position,  and  the  three  pieces  swaged  together.  Kemoved 
from  the  counter-die,  they  are  boiled  in  the  acid  and  again  annealed. 

The  untrimmed  plate  is  placed  in  the  finishing  counter-die  and  swaged. 
It  is  partially  trimmed  at  its  upper  border,  so  that  it  may  be  placed  in 
position  on  the  plaster  model,  which  it  should  fit  with  the  utmost  accuracy. 
If  it  do  not,  it  should  be  reannealed  and  reswaged.  Any  points  of  the 
plate  interfering  with  its  placement  on  the  model  are  to  be  trimmed 
away. 

Plate  No.  2  is  next  placed  in  the  finishing  counter,  and  over  it  the  strip 
of  platinous  gold ;  over  both,  the  larger  plate.  The  die  is  set  in  this, 
and  by  several  heavy  blows  the  swaging  is  completed.  If  there  be  any 
unusual  difficulty  in  removing  the  pieces  from  the  counter-die,  the  pieces 
bending  in  removal,  they  are  to  be  reannealed  and  placed  in  position  on 
the  die  and  covered  by  a  strip  of  the  cloth  enclosing  dental  rubber, 
which  has  been  made  perfectly  pliable  by  soaking  in  water.  The  counter- 
die  is  set  over  this,  and  the  swaging  repeated.  Upon  separating  die  and 
counter,  traction  upon  the  cloth  will  withdraw  the  plates  from  the  counter- 
die.  The  pieces  are  boiled  in  acid,  and  the  surfaces  to  be  united  are 
cleansed  perfectly  by  means  of  brushes  and  pumice,  and  well  washed  and 
dried.  The  strengthening  piece  is  first  united  to  the  larger  plate,  that 
next  to  the  model.  A  thin  mixture  of  borax  is  applied  to  the  surfaces 
of  plate  and  piece  which  are  to  be  united,  and  they  are  bound  together 
by  means  of  binding  wire  holding  the  extremities  and  middle  of  the  sup- 
plementary piece.  A  small  square  of  solder  is  placed  at  one  edge,  and 
the  plate  and  piece  are  heated  uniformly  until  the  solder  flows  between 
them.  If  the  platinous  gold  piece  do  not  change  form  and  separate  at 
any  edge  from  the  plate,  three  more  squares  of  solder  are  placed  one  at 


334  SWAOED  METALLIC  PLATES. 

the  top,  tlie  others  at  the  side  joints,  and  are  flowed  between  the  pieces, 
uniting  them  perfectly.  Boiled  in  acid,  washed,  and  dried,  the  plate  is 
now  placed  on  the  model ;  if  it  have  undergone  any  change  of  form 
during  the  soldering,  it  is  reswaged.  If  not,  the  surfaces  of  the  two 
plates  are  now  painted  with  a  cream  of  borax,  and  hrmly  held  together 
by  means  of  three  or  four  wrappings  of  binding  wire.  No  borax  should 
be  present  on  the  external  portions  of  the  plate.  Along  the  ledge  of  the 
untrimraed  plate,  beneath  the  lower  edge  of  the  trimmed  plate,  a  line  of 
solder  is  placed,  made  of  squares  of  about  an  eighth  of  an  inch  size.  The 
plates  are  warmed  until  efflorescence  of  the  borax  ceases,  and  then  a 
blowpipe  flame  is  directed  beneath  the  plate  until  both  sections  are  heated 
to  a  bright  red,  when  the  solder  will  melt  and  flow  freely  between  the 
plates  and  appear  at  the  opposite  edges.  More  solder  is  added  at  the 
same  place  if  required,  and  it  is  melted  and  drawn  between  the  plates 
until  by  its  filling  of  all  the  joints  it  gives  assurance  that  the  plates  are 
united  throughout.  It  usually  requires  about  a  pennyweight  of  solder 
to  perfectly  unite  the  three  pieces. 

Remove  the  binding  wires  and  boil  the  plate  in  acid.  The  lower 
plate  is  now  trimmed  to  the  outline  of  the  previously  dressed  plates  ;  the 
upper  edges  resting  upon  the  natural  teeth  are  bevelled  lingually,  the 
other  edges  rounded  and  smoothed.  Bending  the  plate  between  the 
fingers  is  now  a  matter  of  difficulty.  It  is  placed  upon  the  model  and 
should  fit  it  perfectly. 

As  a  rule,  these  plates  are  held  in  position  in  the  mouth  by  means  of 
clasps  encircling  two  or  more  of  the  natural  teeth.  These  will  be  de- 
scribed later  in  the  cliapter. 

Clasp  Plates  for  Upper  Dentures. — Occasionally  it  is  necessary  that 
partial  plates  for  the  upper  jaw  be  retained  by  means  of  clasps,  instead 
of  the  vacuum  chamber.  These  plates  are  usually  given  a  horseshoe 
form,  but  it  may  be  that  smaller  devices  are  at  times  applicable. 

The  first  indication  for  the  employment  of  this  type  of  plate  is  such 
a  configuration  or  peculiarity  of  the  palatal  vault  that  the  vacuum  cham- 
ber is  inapplicable. 

Another  class  of  cases  are  those  in  which  the  patient  objects  strenu- 
ously to  the  presence  of  a  plate  of  the  size  necessary  when  a  vacuum 
chamber  is  used. 

In  rare  instances  the  projecting  chamber  is  a  continued  hindrance  in 
enunciation,  and  the  difficulty  is  remediable  through  the  use  of  a  small 
unprojecting  plate. 

Another  class  is  found  in  cases  in  which  artificial  dentures  mounted 
upon  plates  having  vacuum  chambers  are  displaced  by  the  forces  of 
mastication. 

Other  cases  in  which  one  or  more  teeth  are  to  be  replaced  may  be 
retained  by  a  small  plate  held  by  clasps,  where  the  chamber  plate  to  be 
used  would  necessitate  the  wearing  of  a  large  piece. 

Typical  cases  of  the  first  class  mentioned  are  found  in  those 
mouths  presenting  a  large  bony  tuberosity  occupying  the  height  of 
the  vault,  one  or  more  of  the  natural  teeth  absent,  and  deplacement 
is  demanded. 

The  presence  of  a  plate  of  the  size  required  when  a  chamber  is  present 
may  be  productive  of  a  continued  nausea.     Singers,  actors,  and  orators 


CLASP  PLATES  FOR    UPPER  DENTURES. 


335 


occasionally  demand  a  fixture  which  shall  be  firmly  held,  and  which 
shall  not  alter  the  form  of  the  palatal  vault. 


Fig.  371. 


Fig.  372. 


Partial  upper  denture  supported  by  remaining 
teetii. 


Badly -arranged  clasp  plate. 


Fig.  373. 


A  typical  case  of  the  last  class  is  one  for  the  replacement  of  the 
incisors,  the  denture  being  displaced  at  every  attempt  at  biting. 

The  plates  are  always  more  firmly  held  if  the  clasps  are  placed  on 
both  sides,  so  that  the  most  usual 
form  of  these  plates  is  that  of  a 
horseshoe  (Fig.  371).  This  figure 
illustrates  a  typical  clasp  plate 
and  the  indication  for  this  form 
of  denture. 

Figs.  372  and  373  illustrate 
the  form  of  device  obviating  the 
necessity  for  the  employment  of 
an  extensive  plate. 

It  is  determined,  as  described 
later,  the  several  positions  and 
forms  of  the  clasps,  the  bases  of 
which,  as  a  rule,  mark  the  pos- 
terior length  of  the  plate.  The 
latter  is  usually  made  to  enclose 
an  area  of  the  vault  extending 

rarely  less,  and  as  a  rule  more,  than  one-half  of  an  inch  from  the  necks 
of  the  teeth.     The  outline  of  the  plate  is  marked  on  the  model. 

To  ensure  accurate  adaptation  and  sufficient  rigidity  the  plate  is  made 
of  two  laminae  of  No.  30  plate.  One  of  these  is  in  swaging  left  larger 
than  the  other,  so  as  to  form  a  ledge  upon  which  to  place  the  solder  used 
in  uniting  them.  While  soldering  the  plates  are  held  together  by  means 
of  the  clamps  used  when  attaching  chamber-pieces,  but  when  possible 
binding  wire  is  to  be  preferred  :  the  form  of  the  plate,  however,  does  not, 
as  a  rule,  permit  of  this  means  of  holding  the  plates  together.  After 
soldering  the  plate  should  be  trimmed  to  fit  closely  about  the  necks  of 
the  natural  teeth,  but  never  to   rest   upon  the  teeth   themselves.     All 


Supplemental  clasp  to  relieve  strain  on  molar 
tooth. 


336 


SWAGED  METALLIC  PLATES. 


edges  are  next  bevelled  and  smoothed  :  the  posterior  edge  of  the  plate 
should  be  filed  to  a  thin  yet  smooth  edge,  so  that  it  shall  not  be  readily 
perceptible  to  the  tip  of  the  tongue. 

Cases  present  at  intervals  in  which  there  is  a  loss  of  the  bicuspids  and 
two  molars  of  one  side,  the  solitary  molar  standing  as  a  projection  from 
a  rounded  tuberosity,  and  occupying  the  centre  of  the  latter.     The  plate 

Fig.  374. 


form  is  given  this  outline  (Fig.  374),  the  plate  covering  the  tuberosity 
and  perforated  at  the  side  of  the  molar.  The  tooth  reproduced  in  the 
die  is  removed  from  one  and  permitted  to  remain  on  the  other.  The 
stump  left  by  its  removal  is  filed,  giving  it  a  square  edge,  so  that  it  shall 
mark  the  outline  in  swaging.  The  section  is  sawn  out,  beginning  in  a 
perforation  made  with  a  plate-punch. 

After  swaging  on  the  finishing  die  the  perforation  is  filed  away  to  ex- 
pose the  neck-line  of  the  tooth. 

In  making  plates  for  the  class  of  cases  described  in  Chapter  VIII. 
those  having  loose  teeth  in  the  arch  which  are  to  be  removed,  and  have 
a  restoration  by  either  artificial  teeth  or  the  crowns  of  the  natural  teeth 
themselves  fitted  to  the  plate,  a  plate  support  must  be  formed  for  the 
bases  of  the  latter. 

The  impression  taken  and  model  made  and  prepared  as  described  in 
Chapter  VIIL,  the  plate  outline  is  marked  along  a  line  representing  the 
labial  or  buccal  line  of  the  natural  teeth.  Dies  are  made  and  a  plate 
swaged  as  for  an  ordinary  case  :  if  teeth  are  to  be  attached  by  means  of 
soldered  stay  backings,  the  making  of  the  plate  and  the  mounting  of  the 
teeth  do  not  differ  from  those  operations  for  ordinary  cases.  Should  it 
be  designed  to  mount  the  crowns  of  the  natural  teeth  upon  the  plate,  sup- 
ports must  be  provided  for  them. 

Obviously,  the  only  means  by  which  this  may  be  done  is  by  attaching 
posts  to  the  plate,  over  which  the  crowns  are  to  be  cemented.  In  the 
depressions  which  have  been  carved  to  represent  the  gum  outlines  which 
will  exist  as  a  consequence  of  the  extraction  of  the  teeth,  marks  are 
made  to  indicate  the  sites  of  the  pulp-chambers  of  the  teeth.  The  plate 
is  to  be  made  so  that  the  base  of  the  crown  will  rest  upon  it.  This  plate 
extension  is  to  be  perforated  over  each  mark,  and  in  the  direction  of  the 
axes  of  the  teeth  when  these  latter  shall  be  properly  adapted.  The 
openings  are  to  be  countersunk  at  their  under  surfaces.  In  each  open- 
ing a  platinous  gold  wire  No.  16  is  to  be  placed,  tapered  sufficiently  to 
enter  the  opening,  and  be  rigidly  held  in  position  by  the  plate. 

The  countersunk  sides  of  the  openings  and  the  protruding  tips  of  the 
posts  are  touched  with  the  borax  mixture;  a  small  square  of  18-carat 


CLASPS.  337 

solder  laid  beside  each  post.  The  plate  is  heated  from  its  upper  sides  : 
when  at  a  uniform  red  heat  a  fine  flame  is  directed  against  the  plate  at 
the  base  of  each  post,  fusing  and  drawing  through  the  solder. 

The  introduction  of  bridge-work  has  lessened  to  a  great  extent  the 
employment  of  dentures  mounted  upon  clasp  plates.  The  substitution, 
although  a  wise  procedure  in  many  cases,  in  others  is  just  as  clearly  con- 
traindicated.  It  is  undoubtedly  true  that  the 
unilateral  loss  of  teeth,  leaving  a  space  at  the  ends 
of  which  are  teeth  eminently  suitable  as  abutments 
for  the  support  of  a  bridge,  finds  the  best  prosthetic 
appliance  in  a  bridge.  In  point  of  fact,  bridge- 
work  has  even  among  conservative  operators  re- 
placed most  of  the  unilateral  devices,  but  occa- 
sionally the  use  of  plates  for  such  cases  is  still 
found  imperative.  The  introduction  of  the  clasp  of  Dr.  Bonwill  (Fig. 
375)  gives  an  additional  application  of  these  small  plates. 

Clasps. — Clasps  are  metallic  bands  partially  encircling  the  crowns  of 
natural  teeth,  and  serving  as  a  means  for  the  retention  of  artificial  den- 
tures. The  employment  of  the  device  is  prompted  by  necessity,  and  not 
by  choice.  With  upper  plates  they  are  employed  where  the  vacuum 
chamber  is  found  to  be  insufficient  to  retain  a  denture  in  position,  where 
the  configuration  of  the  vault  renders  the  chamber  inapplicable,  or  where 
the  positions  of  the  replaced  teeth  render  the  covering  of  the  vault  with  a 
large  plate  unwarrantable.  They  are  attached  to  partial  lower  dentures 
to  prevent  displacement  by  the  movements  of  the  tongue,  cheeks,  and 
lips,  and  by  the  forces  to  which  these  pieces  are  subjected  during  masti- 
cation. 

The  great  advantage  of  the  employment  of  clamps  is  an  increased 
stability  of  the  piece ;  the  disadvantage  is,  if  worn  long  enough  they 
eventually  cause  the  loss  of  the  crown  of  the  tooth  clasped,  through 
chemical  solution,  not  mechanical  abrasion.  The  food-deposits  beneath 
and  about  the  clasp  are  the  seat  of  lactic  fermentation,  so  that  a  gradual 
solution  of  the  crown  by  lactic  acid  occurs  if  the  clasps  are  not  kept  in 
an  aseptic  condition. 

Not  infrequently,  the  teeth  are  so  mechanically  strained  by  the  force 
of  mastication  transmitted  through  the  clasps  that  the  retentive  appa- 
ratus of  the  teeth  succumbs  and  the  teeth  are  dislodged.  The  latter  is  a 
more  serious  consideration  than  the  loss  of  a  crown  :  an  artificial  substi- 
tute for  the  latter  may  be  provided,  and  serve  for  clasping  ;  but  loosened 
teeth  are  the  b^te  noir  of  dentistry.  This  danger  is  lessened  by  accuracy 
of  adaptation  of  the  plate,  and  by  having  the  clasps  of  sufficient  elasticity 
to  yield  to  stress  and  diminish  the  strain  on  the  teeth. 

Clasps  properly  adapted  serve  but  to  stay  a  plate,  not  to  support  it : 
the  support  should  be  derived  from  uniform  pressure  upon  the  soft  tis- 
sues ;  the  clasps  are  an  adjunct  preventing  displacement.  The  violation 
of  this  principle  is  responsible  for  many  of  the  ills  attributed  to  the 
wearing  of  clasps. 

In  selecting  teeth  to  be  clasped,  where  a  selection  is  possible,  they 
should  be  chosen  with  a  regard  to  their  form,  the  position  and  condition 
of  the  tissues  of  the  teeth,  and  the  surrounding  parts. 

It  is  desirable  that  the  clasps  should  not  be  exposed  by  the  move- 

22 


338  SWAGED  METALLIC  PLATES. 

ments  of  the  lips,  so  that  teeth  posterior  to  the  first  bicuspid  are  prefer- 
ably selected.  To  secure  the  best  adaptation  the  walls  of  the  teeth  should 
be  nearly  parallel.  Conical  teeth,  the  base  of  the  cone  being  at  the  necks 
of  the  teeth,  are  of  improper  form.  A  reversed  relation,  teeth  much 
smaller  at  the  necks  than  at  their  masticating  surfaces,  are  also  of  disad- 
vantageous form.  Freedom  from  caries,  firm  fixation  in  their  sockets, 
and  no  exposure  of  the  cementum  are  desiderata,  and  where  and  when 
it  is  possible  to  secure  these  features  they  are  to  be  regarded  as  essentials. 
In  the  event  of  the  absence  of  a  latitude  of  choice  certain  precautions 
are  to  be  observed.  Carious  cavities  are  to  be  perfectly  filled  and  per- 
fectly finished  and  the  teeth  to  undergo  periodical  examination.  Should 
there  be  any  recession  of  the  gum,  exposing  the  cementum  of  the  tooth, 
the  clasp  must  embrace  none  but  enamel  surfaces.  Exposure  of  cemen- 
tum indicates  loss  of  a  portion  of  the  retentive  apparatus  of  the  tooth,  a 
relative  lengthening  of  the  crown,  and  hence  an  increased  leverage  upon 
the  socket  of  the  tooth ;  stress  is  lessened  by  making  the  clasp  of  thinner 
metal. 

Clasping  loose  teeth  always  results  in  their  loss,  and  is  justifiable  only 
under  extremely  rare  circumstances,  and  then  the  clasp  should  be  very 
light  and  elastic. 

Clasps  should  be  so  adapted  to  the  teeth  upon  which  they  are  worn 
that  there  shall  be  no  projections  acting  as  sources  of  irritation  to  the 
tongue  or  cheeks.  All  of  the  edges  should  have  a  rounded  bevel  and  be 
made  perfectly  smooth. 

The  length  of  a  clasp  is  of  two  parts  as  to  function — one,  serving  as 
the  part  of  attachment  to  the  plate ;  the  other  consists  of  one  or  two  free 
ends  which  admit  of  form  change,  grasping  the  tooth  and  holding  by  the 
elasticity  of  the  metal. 

These  free  ends  should  have  perfect  elasticity,  in  so  far  as  the  prop- 
erty is  present  in  the  platinous  gold  alloy  ;  they  should  permit  sufficient 
yielding  to  allow  the  wing  of  the  clasp  to  be  carried  over  a  tuberosity, 
and  return  to  their  original  forms  as  soon  as  the  stress  is  removed. 
The  perfect  elasticity  is  due  in  great  part  to  the  form  of  the  clasps. 

The  strain  upon  the  metal  itself  is  at  its  narrowest  part,  so  that  if 
this  part  be  at  the  point  or  slightly  beyond  the  point 
Fig.  376.     Fig.  377.     of  the  attachment  to  the  plate,  the  elasticity  is  mark- 
edly lessened  and  there  is  danger  of  breakage  (Fig. 
376). 

The  maximum  of  elasticity  is  secured  by  having 
the  greatest  thickness  of  the  metal  at  the  angle,  and 
diminishing  its  thickness  toward  the  free  extremity 
of  the  clasp  (Fig.  377). 

When  a  choice  offers  as  to  the  passing  a  clasp 

with  its  body  across  the  distal   or  mesial  wall  of  a 

Fig-  376  clasp  weaken-     tooth,  it  is  usual  to  place  it  ou  the  distal  wall  as  the 

er  edge.  better  position  to  resist  displacement  of  the  denture, 

^'shS'd^^^'^  properly    ^i^^^y^  provided  the  distal  wall  be  not  too  short  and 

inclined  from  the  back. 

The  free  ends  of  a  clasp  when  possible  are  to  be  at  the  buccal  aspect 

of  the  tooth. 

Greater  stability  is  afforded  by  having  a  clasp  embrace  as  much  of 


CLASPS. 


339 


Fig.  378. 


Fig.  379. 


the  enamel  surface  of  a  tooth  as  possible.  Each  individual  case  is  a  rule 
for  itself  as  to  the  manner  of  placement  of  clasps.  The  operator  by  an 
examination  of  the  teeth  of  the  model  and  of  a  careful  scrutiny  of  the 
natural  organs  determines  the  teeth  which  shall  afford  the  best  bases  for 
clasps  and  secure  the  greatest  stability  to  an  artificial  denture.  Fre- 
quently it  is  necessary  to  modify  the  form  and  size  of  a  plate  according 
to  necessities  arising  out  of  the  enforced  selection  of  clasp 
teeth. 

The  outlines  of  the  future  clasp  are  plainly  marked  on 

the  plaster  teeth  by  mean  of  a  blue  pencil.     If  the  cemen- 

tum  of  the  tooth  be  exposed,  the  clasp  is  not  to  pass  beyond 

the  enamel  border.     At  the  side  of  the  attachment  to  the 

plate  it  is  made  the  section  of  a  cylinder  extending  from 

just  below  the  grinding  surface  of  the  tooth  to  the  plate  at 

its  neck  (Fig.  378).     This  form  is  frequently  necessary  with 

the  clasps  of  partial  lower  dentures.     For 

extremely  short  crowns   the  clasp  is  made 

of  half-round  platinous  gold  wire. 

A  pattern  of  the  clasp  is  to  be  made 
of  heavy  pattern  tin  closely  adapted  to  the 
plaster  tooth  and  trimmed  to  correspond 
exactly  with  the  pencil-marks.  The  ex- 
ternal free  ends  of  the  clasps  are  plainly 
marked  so  as  to  distinguish  each  when 
flattened.  They  are  flattened  between  the 
fingers.  As  a  rule,  the  thickness  of  the 
metal  should  be  greater  with  increase  in  the 
length  of  the  free  ends.  Clasps  are  rarely 
made  lighter  than  No.  26  gauge,  and  never 
heavier  than  No.  22.  Wide  clasps  having 
comparatively  short  free  ends,  and  which 
are  subjected  to  light  stress,  are  made  of 
No.  26  ;  those  having  long  and  narrow  free 
ends  are  made  of  the  heavier  numbers. 
The  average  thickness  is  No.  25. 

The  patterns  are  reproduced  in  the  clasp 
metal,  the  edges  of  the  latter  being  filed  to 
conform  perfectly  with  those  of  the  tin 
pattern. 

Three  pairs  of  pliers  are  usually  sufficient 
to  shape  the  various  forms  of  clasps — a  pair 
of  four  inch  round-nose  pliers  to  bend  the 
clasp  at  its  angles  ;  a  pair  of  four  inch  flat- 
nose  pliers,  having  sloping  beaks — these 
to  adapt  the  flat  aspects  of  the  clasp  ;  a  pair 
of  four  inch  round-nose  pliers,  bent  to  a 
curve  of  about  one  inch  radius  (Fig.  379) 
— these  are  used  to  make  the  clasp  con- 
form to  rounded  surfaces  of  the  clasp  tooth. 
Some  operators  prefer  a  special  pair  of  pliers  for  this  purpose — what  are 
known  as  clasp-benders:  the  skilful  mechanic  usually  finds  them  needless. 


Curved  pliers. 


340  SWAGED  METALLIC  PIRATES. 

The  metal  is  well  annealed.  Usually  the  bending  is  begun  in  the 
middle  of  the  clasp,  unless  one  extremity  of  the  latter  should  be  between 
two  teeth,  when  that  extremity  is  adapted  first.  Work  from  the  middle 
toward  either  end,  changing  the  pliers  when  necessary  to  make  the  clasp 
conform  to  the  surface  of  the  plaster  tooth.  When  the  clasp  tooth  has 
been  accurately  reproduced  on  the  die,  the  clasp  may  be  first  bent  to  this 
and  the  fitting  completed  on  the  plaster  tooth.  It  is  a  wise  precaution  to 
give  the  plaster  teeth  a  coat  of  thin  sandarac  varnish  before  bending  the 
clasps  to  them  to  prevent  any  abrasions  of  the  surface  of  the  plaster. 
When  the  clasp  has  been  made  to  conform  perfectly  with  the  surface 
enclosed  by  the  pencil-marks  made  on  the  plaster  tooth,  its  edges  are 
given  a  rounded  bevel ;  they  are  smoothed  with  emery-cloth  and  buifed 
with  pumice  or  a  felt  cone.  The  extremity  or  extremities  which  are  not 
to  be  attached  to  the  plate  are  bent  away  from  the  plaster  tooth,  so  that 
the  clasps  may  be  readily  withdrawn. 

It  is  desirable  that  the  axes  of  the  clasp  teeth  be  nearly  or  quite 
parallel.  Should  this  not  be  the  case,  the  cervix  of  one  clasp  must  stand 
off  from  the  neck  of  the  tooth,  so  that  the  lingual  walls  of  the  several 
clasps  are  parallel.  Violation  of  this  precaution  may  render  it  impossible 
to  withdraw  the  fixture  from  the  model,  when  the  clasps  are  cemented  to 
the  plate,  without  disturbing  the  mutual  relations,  or  make  it  equally 
impossible  to  place  the  fixture  in  the  position  in  the  mouth  when  the 
clasps  are  attached  to  the  plate  with  solder. 

The  plate  is  placed  on  the  model,  and  one  clasp  set  over  its  tooth  :  any 
points  of  the  plate  interfering  with  the  placement  of  the  clasp  in  its  true 
position  are  to  be  filed  away  until  the  clasp  is  properly  adjusted,  and  its 
junction  with  the  plate  is  represented  by  a  line.  The  plate  is  cut  away 
in  the  same  manner  to  permit  the  adjustment  of  the  other  clasp  or  clasps. 

It  is  advisable  to  now  attach  the  clasps  very  lightly  to  the  plate,  so 
that  they  are  held  by  but  one  point,  permitting  the  making  of  any 
changes  in  the  form  of  the  clasp  which  may  be  found  necessary  when  the 
fixture  is  placed  in  the  mouth.  Occasionally  the  soft  tissues  of  the  mouth 
yield  so  much  to  the  pressure  of  the  plate  that  the  same  relations  are 
not  present  between  the  pieces  in  the  mouth  as  they  were  on  the  model ; 
and  if  the  attachment  of  the  clasps  to  the  plate  be  too  extensive,  there 
is  no  latitude  for  making  the  necessary  changes  in  the  pieces. 

The  clasps  are  fastened  to  the  plate  by  means  of  adhesive  wax  made 
very  hot :  short  sections  of  wire  to  extend  at  an  angle  from  the  top  of 
the  clasp  to  the  plate  are  heated  and  laid  in  the  cement.  These  pre- 
vent fracture  of  the  latter  in  removal  of  the  fixture  from  the  model. 
When  the  cement  is  hard,  the  plate  with  the  clasps  attached  is  care- 
fully lifted  from  the  model,  so  that  the  cement  attaching  the  clasps  is 
not  broken.  About  a  couple  of  tablespoonsful  of  beach  sand  are  placed 
in  a  plaster-bowl  and  just  covered  with  water ;  plaster  is  dusted  into  this 
and  stirred,  making  a  thick  batter,  with  which  the  plate  and  clasps  are 
filled  from  the  palatal  side  and  nearly  covered  upon  the  lingual  portion. 
When  the  investment  is  hard  the  cement  is  picked  away,  and  a  sharp- 
pointed  scraper  passed  along  the  joints  between  clasps  and  plate  to 
furnish  a  fresh  surface  for  soldering.  As  but  a  small  attachment  is  to 
be  made  at  this  time,  all  of  the  joint  except  one-eighth  of  an  inch  of  its 
length  is  filled  with  a  paste  of  whiting. 


PARTIAL  CLASPS.  341 

The  point  of  soldering  is  made  usually  at  the  mesio-palatal  angle. 
Borax  is  applied  to  this  portion  of  the  joint  and  a  minute  piece  of 
plate  laid  over  it.  Two  very  small  pieces  of  solder  are  covered  with 
borax,  and  one  laid  on  the  plate,  the  other  on  the  clasp  above  the  joint. 
The  mass  is  heated  on  a  furnace,  and  then  on  a  charcoal  bed  under  the 
blowpipe  until  it  is  a  uniform  red,  when  a  fine  blowpipe  flame  directed 
on  the  plate  just  beyond  the  joint  causes  the  solder  to  flow  and  attach 
the  clasps  to  the  plate.  When  cold  the  plate  is  boiled  in  acid  and  buffed, 
and  is  ready  for  trial  in  the  mouth. 

When  the  tissues  of  the  arch  and  vault  are  softer  than  usual,  their 
yielding  alters  the  relations  of  the  clasp  and  plate.  When  this  softness 
is  found  to  exist,  it  is  advisable  to  test  the  adaptation  of  the  pieces,  both 
plate  and  clasp,  before  attaching  the  latter  by  means  of  solder.  The 
plate,  with  the  clasps  cemented  in  position,  is  placed  in  the  mouth  ;  the 
plate  is  pressed  into  position,  the  clasps  are  pressed  into  apposition  with 
the  natural  teeth.  A  small  piece  of  sponge  saturated  with  ice-water  is 
then  laid  upon  the  wax  until  it  is  perfectly  hard,  when  plate  and  clasps 
are  removed,  placed  in  an  investment,  and  soldered. 

Partial  Clasps. — Any  support  which  embraces  less  than  two-thirds 
of  the  periphery  of  a  crown  may  be  fitly  termed  a  partial  clasp.  Such 
appliances  are  designed  mainly  as  braces.  They  are  employed  upon  the 
palatal  surfaces  of  bicuspids  where  no  space  exists  through  which  a 
clasp  may  be  carried,  and  where  a  plate,  as  for  one  tooth,  may  fre- 
quently be  retained  by  bracing.  Occasionally  it  is  necessary  to  make 
the  space  between  the  teeth  by  means  of  a  file,  subsequently  smoothing 
and  polishing  the  cut  surface  of  the  tooth.  Such  mutilation  is  to  be 
regarded  as  an  unmixed  evil  and  never  to  be  practised  unless  absolutely 
necessary. 

Placed  upon  bicuspids,  these  devices  are  usually  made  in  pairs  for 
the  first  and  second  bicuspids.  The  ends  are  to  be  made  thin,  so  as  to 
extend  as  far  as  possible  between  the  teeth, 

the  bodies  of  the  pieces  covering  the  palatal  ^^®-  ^^0.  Fig.  381. 

surfaces  of  the  teeth  (Fig.  381). 

When  the  bicuspids  and  molars  of  the 
lower  jaw  are  all  lost,  and  the  lingual  wall 
of  the  cuspids  sloping  so  that  a  large  clasp 
covering  it  would  prevent  the  plate  from 
settling  into  position,  a  half  clasp  is  applied, 
grasping  the  cervical  half  of  the  labial  face 
(Fig.  380).  The  same  device  is  applicable 
to  the  superior  cuspids.  The  exposed  ends 
of  such  clasps  may  be  made  to  resemble  gold  fillings  by  filing  the  edges 
thin  and  soldering  to  them  a  layer  of  pure  gold.  A  piece  of  the  latter 
metal  of  No.  31  gauge  is  annealed  and  burnished  over  the  clasp,  the  sur- 
faces covered  with  borax,  and  united  by  means  of  20-carat  solder. 

With  small  saddle  plates,  or  partial  lower  plates  which  exhibit  an 
undue  tendency  to  bury  themselves  in  and  irritate  the  soft  tissues,  an 
inverted  L  made  of  half-inch  round  wire  is  soldered  to  the  clasps,  resting 
upon  the  grinding  surfaces  of  the  teeth.  This  device  is  particularly 
useful  for  partial  lower  dentures,  when  the  third  molars  are  remaining 
(Fig.  369),  it  being  necessary  to  dress  the  plate  away  to  permit  placing 


342 


SWAGED  METALLIC  PLATES. 


it  in  position,  so  that  its  posterior  extremity  is  driven  into  the  gum  at 
every  attempt  at  mastication.  In  such  cases  the  L  is  frequently  used 
without  a  clasp. 

Dr.  Bonwill  has  recently  furnished  a  solution  to  a  class  of  cases 
which  heretofore  has  baffled  the  skill  of  the  prosthetist.  These  are 
partial  cases  in  which  the  axes  of  the  natural  teeth  have  been  at  such 
angles  to  one  another  as  to  make  the  adjustment  of  plate  and  clasps  by 
ordinary  means  impossible.  Such  a  case  is  illustrated  in  Fig.  385.  The 
lingual  cavity  had  the  form  of  a  frustum  of  a  cone,  the  base  of  a  cone 
the  floor  of  the  mouth,  the  top  of  the  frustum  the  cutting  edges  of  the 
teeth.  The  device  necessary  for  this  case  would  have  been  ineffective 
without  the  peculiar  clasp  support  introduced  by  Dr.  Bonwill. 

When  trimmed,  it  was  found  that  the  ordinary  partial  lower  plate 
could  not  be  adjusted  to  such  a  model,  the  distance  between  the  edges 
of  the  teeth  and  their  bases  being  so  marked  that  it  would  be  impossible 
to  insert  a  plate  in  any  other  way  than  from  without  inward,  thus  vir- 
tually necessitating  the  plate  support  proper  to  be  at  the  labial  and 
buccal  aspects  of  the  ridge. 

The  plaster  teeth  were  sawn  half  through,  then  broken  off,  leaving 
a  sharp  line  of  fracture,  and  all  of  them  preserved. 

Dies  were  then  made ;  a  brass  plate  swaged  of  sufficient  size  to  sup- 
port the  teeth.  Openings  were  made  in  the  plate  corresponding  with  the 
bases  of  the  incisor  and  bicuspid. 

The  plaster  teeth  were  now  cemented  to  place  on  the  model. 

The  trial  plate  of  brass  was  tried  to  the  model,  and  cut  away  at  all 
points  interfering  with  its  placement  upon  the  ridge,  and  at  the  com- 
pletion of  this  process  had  acquired  the  irregular  form  represented  in 
Fig.  282 ;  a  saddle  resting  upon  the  alveolar  ridge,  and  having  two 
apertures  much  enlarged  to  permit  passage  over  the  isolated  teeth  at  its 
extremities,  dressed  away  to  allow  passing  over  the  overhanging  edges 
of  left  inferior  second  bicuspid  and  right  inferior  second  molar. 

The  plate  was  reproduced  in  gold,  using  two  laminae  of  No.  29. 
This,  when  placed  in  the  mouth,  was  found  to  have  a  lateral  movement 
upon  pressure,  due  to  its  lack  of  contact  with  the  natural  teeth. 


Fig.  382. 


Fig.  383.    Fig.  384. 


Ordinary  clasps  for  such  a  case  are  out  of  the  question,  so  on  the 
molar  and  bicuspid  partial  clasps  were  made  of  the  pattern  suggested 
by  Dr.  Bonwill,  having  in  the  middle  of  each  an  inverted  L  resting 
upon  the  masticating  surfaces  of  the  teeth,  and  protecting  against  the 
extremities  of  the  plate  burying  in  the  gum.  The  Ls  were  made  of 
half-round  platinous  gold,  the  lower  end  extending  to  the  plate  and 
soldered  to  it,  this  extension  serving  as  an  elastic  supporting-bar 
(Fig.  383). 


PARTIAL   CLASPS. 


343 


The  clasp  upon  the  left  bicuspid  (Fig.  383)  was  arranged  somewhat 
differently  from  the  molar  clasp  in  that  its  attachment  to  the  L  support 
was  at  almost  its  lingual  extremity.  This  was  done  to  increase  the 
spring-like  action  of  the  clasp  and  enable  it  to  pass  easily  to  position 
without  interfering  with  the  perfection  of  its  grip  upon  the  tooth  when 
the  denture  was  finally  in  place. 

Prior  to  attaching  these  clasps  both  apertures  in  the  plate  were  sur- 
rounded by  a  heavy  triangular  gold  wire,  to  prevent  irritation  by  a  thin 
edge  at  these  places. 

Plain  teeth  were  fitted  to  the  plate,  backed  and  soldered,  and  along 
the  external  wall  of  the  plate  an  artificial  gum  was  made  of  the  mixed 
rubber  known  as  Walker's  granular  gum. 

Fig.  385,  A,  represents  the  finished  piece,  and  Fig.  385,  B,  the  same  in 
position  upon  the  model. 

The  bars  which  attach  plate  and  clasp  are  placed  at  the  plate  edge 
opposite  to  the  overhanging  wall  of  the  tooth,  so  that  the  elasticity  of  the 
bar,  while  permitting  the  placing  of  the  clasp  over  the  overhanging  wall, 


draws  it  close  to  the  latter  when  the  denture  is  in  position.  It  was  found 
necessary  in  the  case  illustrated  to  attach  both  clasps  by  posts  placed  at 
the  disto-buccal  angles  of  the  plate.  Dr.  Bonwill  applies  the  device  with 
small  saddle  plates  carrying  one  or  two  teeth  when  the  clasp  teeth  are 
much  inclined,  and  its  application  is  eminently  satisfactory. 

A  class  of  partial  lower  cases  will  be  met  with  in  which  the  dentures 
made  for  them  have  a  tendency  to  slip  from  position  backward.  Clasps 
applied  to  the  natural  teeth  but  insufficiently  overcome  this  tendency. 


344 


SWAGED  METALLIC  PLATES. 


Prof.  C.  J.  Essig  has  devised  an  adjunct  to  the  plate  which  effectually 
overcomes  this  difficulty.  In  swaging  the  plate  the  anterior  end  of  the 
buccal  portion  is  carried  farther  forward  than  usual.  A  die  and  counter- 
die  are  made  of  the  labial  wall  of  the  model,  and  two  strips  of  metal  are 

Fig.  386. 


swaged,  one  of  No.  28  plate,  the  other  of  No  27  platinous  gold,  and  made 
to  fit  this  wall  above  the  necks  of  the  teeth.  The  pieces  are  soldered 
together,  and  their  extremities  are  joined  to  the  lengthened  plate,  the 


Fig.  387. 


pieces  invested  and  soldered.  A  modification  of  this  idea,  and  suggested 
by  it,  is  the  device  shown  in  Fig.  287.  It  is  designed  to  lessen  the 
strain  upon  the  natural  teeth  due  to  the  force  of  mastication  acting  at  an 
unusual  angle.     It  subserves  its  purpose  perfectly. 

Swaging-  with  Shot. — An  apparatus  and  method  have  been  devised 
by  Dr.  Parker  of  Grand  Rapids,  Mich.,  through  which  the  adaptation  of 
aplate  to  a  model  may  be  secured  with  a  greater  degree  of  accuracy  than 
attainable  by  swaging  between  dies  and  counter-dies.  The  apparatus  con- 
sists of  a  heavy  cast-iron  cylinder  having  a  thick  bottom.  The  chamber 
of  the  cylinder  is  about  four  inches  in  diameter,  large  enough  to  freely 
admit  the  base  of  a  large  plaster  model.  The  cylinder  A  is  bored  for  the 
reception  of  a  heavy  plunger  having  a  concave  face,  B  ;  the  plunger  is 
turned  to  fit  the  cylinder.  The  plate  is  approximately  adapted  to  the 
plaster  model  by  means  of  dies  and  counter-dies.  Fine  bird  shot  is 
placed  in  the  cylinder  until  it  is  filled  to  about  an  inch  or  more  above 


ELECTRO-DEPOSIT  PLATES. 


345 


the  alveolar  edge  of  the  model.     The  plunger  is  placed  in  position  and 
its  cylindrical  head  struck  several  times  with  a  heavy  hammer.     The 


Fig.  388. 


pressure  of  the  shot,  evenly  distributed  over  the  entire  plate  area,  drives 
the  plate  into  accurate  apposition  with  the  plaster  model.  The  plaster 
model  itself  is  made  to  serve  as  a  die.  The  plate  is  adapted  by  means 
of  dies  and  counter-dies  as  closely  as  possible,  when  it  is  annealed, 
placed  on  the  plaster  model,  and  the  swaging  accomplished.  The  shape 
of  the  plunger  is  such  that  the  shot  about  the  labial  and  buccal  walls  of 
the  plate  is  first  compressed,  supporting  the  model  laterally ;  the  suc- 
ceeding pressure  is  upon  the  palatal  portion  of  the  plate,  forcing  it  into 
accurate  apposition  with  the  model.  The  model,  supported  equally  on 
all  sides,  is  not  fractured. 

Electro-deposit  Plates. — This  variety  of  plate  was  designed  to  com- 
bine the  advantages  of  a  metallic  plate  with  the  accuracy  of  adaptation 
of  those  constructed  of  the  vegetable  bases. 

Its  method  of  making  is  thus  described  by  Dr.  C.  S.  Stockton  :  A 
plaster  model  is  obtained,  upon  which  reliefs,  chamber,  and  rim  outlining 
ridge  are  built  of  plaster.  The  model  is  boiled  for  a  few  minutes  in  wax 
or  paraffin.  The  surface  to  be  embraced  by  the  plate  is  coated  with 
plumbago.  The  model  is  immersed  in  a  silver  solution  and  connected 
with  the  battery  as  in  any  silver-plating  operation  :  it  is  permitted  to 
remain  in  the  solution  for  four  or  five  days,  when  it  is  withdrawn.  The 
deposited  silver  is  removed  from  the  model,  trimmed  to  the  correct  plate 
outlines,  and  polished.  The  surface  to  be  covered  by  the  vulcanite  at- 
tachment is  roughened.  The  plate  is  now  immersed  in  the  gold  bath  to 
deposit  sufficient  gold  to  permit  of  perfect  vulcanization.  The  teeth  are 
next  attached  by  means  of  vulcanite,  and  the  piece  returned  to  the  gold 
bath,  where  it  is  to  remain  until  three  or  four  pennyweights  of  gold  are 
deposited.  The  principal  objection  to  this  form  of  plate  is  its  tendency 
to  tarnish,  the  gold  plating  not  being  impervious. 


CHAPTER   X. 

THE     "BITE"    OR    OCCLUSION. 

By  Grant  Molyneaux,  D.  D.  S, 


The  lower  jaw  forms,  with  the  temporal  bone,  a  joint  called  the 
"  teraporo-maxillary  articulation."  This  joint  is  formed  by  the  con- 
dyle of  the  lower  jaw,  which  is  of  oblong  form  and  is  convex  from 
side  to  side  and  antero-posteriorly,  resting  in  a  concavity  of  the  tem- 
poral bone  called  the  glenoid  fossa.  It  permits  of  a  hinge-like  motion, 
a  gliding  motion,  and  a  rotary  motion,  each  of  which  is  limited  by  the 
articular  ligaments.  The  lower  jaw  is  endowed  with  these  movements 
to  permit  the  proper  incising  and  masticating  of  the  food. 

When  all  the  teeth  have  been  removed  and  artificial  dentures  are  con- 
templated these  movements  become  a  matter  of  serious  consideration  to 
the  dentist,  as  he  is  compelled  to  accurately  locate  the  lower  jaw  in  those 
positions  and  in  the  position  of  occlusion.  The  lower  jaw  has  only  one 
position  of  complete  occlusion,  and  that  is  when  both  condyles  are  resting 
in  the  glenoid  fossae  and  the  mouth  is  closed. 

Fig.  389. 


Skull  showing  temporo-maxillary  articulation,  and  natural  teeth  in  occlusion. 

The  position  of  the  jaw  is  best  studied  from  the  skull  (Fig.  389), 
which  shows  the  temporo-maxillary  articulation,  A,  and  the  teeth  striking 
ao-ainst  each  other.     The  teeth  as  shown  in  the  cut  are  in  the  position  of 

346 


BITES  FOB  ENTIBE  ABTIFICIAL  DENTUBES. 


347 


occlusion,  and  when  the  mouth  is  merely  opened  and  closed  without  any- 
lateral  or  forward  motion  it  is  called  the  motion  of  occlusion. 

It  is  the  motion  of  occlusion  which  it  is  so  necessary  to  secure  when 
about  to  construct  an  artificial  denture,  for,  before  we  can  arrange  any  of 
the  artificial  teeth  we  must  obtain  either  the  position  of  the  teeth  of  the 
opposing  jaw  in  occlusion,  or,  if  there  are  no  opposing  teeth,  the  correct 
relation  of  the  edentulous  ridges. 

The  operation  of  obtaining  the  occlusion  of  the  jaw  is  generally 
termed  the  "  taking  of  the  bite."  The  taking  of  the  occlusion  would 
seem  to  be  a  better  term,  but,  as  the  former  term  has  the  sanction  of 
long  usage,  is  shorter,  and  is  perfectly  understood.  The  "  taking  of  the 
bite,"  then,  is  simply  obtaining  the  relation  of  the  jaws  in  occlusion. 
This  is  best  studied,  by  the  beginner,  from  a  patient  with  all  of  the 
teeth,  upper  and  lower,  in  situ. 

In  its  simplest  form  it  consists  of  placing  a  roll  of  soft  wax  about  as 
thick  as  the  index  finger  between  the  teeth,  and  long  enough  to  extend 

Fig.  390. 


Upper  cast,  with  temporary  base-plate  in  position. 

from  the  last  tooth  on  one  side  to  the  last  tooth  on  the  other,  and  have 
the  patient  bite  into  it. 

The  patient  is  directed  to  bite  or  close  the  teeth  into  the  wax  until  the 
opposing  teeth  strike  each  other,  and  while  holding  them  steadily  in  this 
position  the  soft  wax  is  pressed  close  against  the  surfaces  of  all  the 
teeth,  care  being  taken  to  prevent  the  patient  from  changing  the  position 
of  the  lower  jaw  after  the  bite  has  been  secured.  The  wax  should  then 
be  chilled  by  a  stream  of  cold  water  from  a  syringe  to  prevent  bending, 
when  the  wax-bite  can  be  easily  removed. 

This  wax-bite  will  contain  an  impression  of  the  upper  teeth  on  one 
side  and  the  lower  teeth  on  the  other.  After  this  is  accomplished  an 
upper  and  lower  impression  of  the  teeth  in  the  mouth  should  be  taken. 

When  these  casts  are  recovered  from  the  impression  they  are  to  be 
placed  in  their  respective  positions  in  the  wax-bite,  and  fastened  together 
by  a  wire  or  other  means  to  permit  of  the  wax  being  removed  without 
changing  the  position  of  the  casts. 

If  after  the  wax  is  removed  the  casts  are  found  to  bear  the  same 
relation  to  each  other  as  the  teeth  in  the  mouth,  the  bite  is  correct. 

Bites  for  Entire  Artificial  Dentures. — The  first  step  in  taking  a 


348 


THE  "BTTE"    OB   OCCLUSION. 


bite  for  entire  dentures  is  to  adjust  to  the  casts,  temporary  base-plates. 
These  base-plates  are  about  three  thirty-seconds  of  an  inch  in  thickness, 
and  are  formed  in  sheets  of  either  gutta-percha,  beeswax,  paraffin,  or  pat- 
tern tin.  The  kind  usually  employed  is  composed  largely  of  paraffin, 
with  a  pink  tint — "  pink  paraffin  base-plates."     A  sheet  of  this  is  warmed 


Fig.  391. 


Lower  cast,  with  temporary  base-plate  in  position. 

unifornily  to  soften  it,  when  it  is  laid  over  the  entire  ridge  of  a  lower 
cast  (Fig.  391)  and  over  the  ridge  and  palatal  portion  of  an  upper  cast, 
as  illustrated  in  Fig.  390.  In  pressing  these  plates  down  upon  the 
casts  care  must  be  taken  not  to  reduce  their  thickness  at  any  point  by  too 

great  force,  as  they  represent  the  thick- 
ness of  tlie  future  jjermanent  base,  and 
any  inequality  of  the  permanent  base 
would  materially  weaken  it. 

The  edges  of  the  wax-plate  should 
now  be  trimmed  to  conform  to  the 
attachment  of  muscles  on  the  ridge, 
which  would  make  the  upper  plate 
higher  in  the  incisive  and  cuspid  re- 
gion and  over  the  tuberosities,  and 
lower  in  the  buccal  region,  as  shown  in 
Fig.  390,  B.  The  lower  wax-plate  must 
1  e  trimmed  to  rest  easily  on  the  ridge 
dthout  impinging  upon  the  muscles  on 
ither  side  of  the  ridge  (Fig.  391). 

A  roll  of  soft  beeswax  is  now  placed 
pon  the  base-plate  large  enough  to 
cover  the  entire  ridge,  about  half  an 
inch  high  and  about  three-fourths  of  an 
inch  wide.  This  is  pressed  down  upon 
the  base-plate  so  that  it  will  cover  the 
labial  and  buccal  side  and  extend  an 
equal  distance  over  the  lingual  side  of 
the  ridge,  as  shown  in  Fig.  392. 

These  plates  are  called  "  articulating 
plates,"  and  after  chilling  them  in  cold  water  they  are  ready  to  try  in  the 
mouth.     The   upper  plate  is  now  placed  in  the  mouth,  and  the  length 


Showing  the  wax  base-plates,  temporary 
or  trial  plates,  with  bite-wax  in  posi- 
tion :  A,  upper  bite-plate ;  B,  lower  bite- 
plate. 


BITES  FOR  ENTIRE  ARTIFICIAL  DENTURES. 


349 


of  the  lip  marked  by  trimming  the  occluding  surface  of  the  bite- 
wax  until  it  is  the  exact  length  of  the  upper  lip,  being  careful  when 
trimming  to  take  off  the  wax,  so  that  the  occluding  edge  will  repre- 


FiG.  393. 


/.   ! 


No.  1. 


No.  2. 


No.  3. 


sent  the   exact  plane  of  the  cutting  edges  of  the  incisor  teeth.     The 
lower   bite-plate    is   then    placed   in    the    mouth,    and    trimmed   ante- 


350 


THE  "BITE"    OR   OCCLUSION. 


riorly  to  represent  the  desired  length  of  the  lower  teeth.  After  the 
occluding  surface  of  the  bite-wax  is  trimmed  to  give  the  length  of  the 
teeth,  the  bite-plates  should  be  returned  to  the  cast,  and  if  they  have 
changed  shape  they  should  be  again  warmed  and  readapted  to  the  casts, 
after  which  they  should  be  cooled  and  returned  to  the  mouth.  The 
patient  should  then  be  instructed  to  gently  close  the  mouth  while  the 
operator  holds  the  plates  in  position  on  the  ridges.  It  must  now  be 
carefully  observed  whether  the  occluding  surfaces  of  the  bite-wax  strike 
uniformly  against  each  other.  If  there  is  a  space  between  them  at  any 
point,  either  the  point  which  strikes  must  be  trimmed  off  or  w^ax  must  be 
added  when  required  in  order  to  have  the  blocks  strike  solidly  against  each 
other  over  the  entire  occluding  surface.  As  the  anterior  part  of  the  wax  has 
been  trimmed  to  give  the  length  of  the  teeth,  this  should  not  be  disturbed. 
If,  however,  the  plates  come  together  anteriorly  and  not  posteriorly, 
w^ax  should  be  added  in  order  to  prevent  them  tilting.  After  the  ope- 
rator has  obtained  an  even  contact  between  the  bite-pieces  when  the 
patient's  mouth  is  closed,  he  must  "  fix  "  the  bite.  This  is  accomplished 
by  making  two  or  three  parallel  cuts  in  the  two  waxes  while  in  correct 
position ;  these  cuts,  together  wnth  one  marking  the  central  line,  will 
serve  as  guides  in  maintaining  their  correct  relation. 

While  this  is  being  done  the  patient  should  be  in  a  comfortable 
position,  and  no  definite  instruction  given  about  closing  the  mouth, 
being  directed  to  swallow  and  at  the  same  time  to  close  the  mouth. 
The  act  of  swallowing  will   involuntarily  bring  the   lower  jaw   into 

Fig.  394. 


Wax-bite  plates  and  casts  in  position :  A,  median  line  of  face ;  B,  high  lip-line ;  C,  low  lip-line ;  D, 

occluding  surfaces  or  lip-line. 

the  position  of  occlusion:  the  operator  instructs  the  patient  to  bite  hard 
until  directed  to  relax.  The  softened  edges  of  the  wax  are  thus  brought 
into  such  forcible  occlusion  that  they  cannot  be  separated,  and  the  occlu- 
sion of  the  jaws,  or  the  bite,  is  fixed.  The  wax-plates,  upper  and  lower, 
may  then  be  removed  in  one  piece.  The  casts  should  be  adjusted  in  the 
base-plates,  and  with  a  hot  spatula  the  two  bite-plates  should  be  securely 
fastened  to  each  other  by  melted  wax,  when  they  should  be  again  cooled 
and  returned  to  the  mouth.  At  this  point  is  determined  the  exact  con- 
tour of  the  patient's  face  by  adding  wax  to  the  labial  surface  of  the  bite- 


THE  ARTICULATOR. 


351 


wax,  or  by  reducing  the  latter  until  the  natural  expression  of  the  patient's 
face  is  restored. 

The  next  point  to  determine  is  the  high  and  low  lip-lines. 

The  occluding  edges  of  the  bite-plates  represent  the  length  of  the 
lips  at  rest,  as  well  as  the  length -of  the  teeth.  The  high  lip-line  is  the 
highest  point  of  elevation  of  the  upper  lip,  as  when  laughing ;  the  low 
lip-line  is  the  lowest  point  to  which  the  lower  lip  is  depressed.  The 
next  line  is  the  median  line  of  the  face,  which  should  be  made  on  the 
wax  perpendicular  to  the  occluding  surface  of  the  wax-bite.  These 
lines  are  marked  on  the  wax  with  a  sharp  instrument,  and  are  shown 
in  Fig.  394. 

The  bite  with  all  the  markings  is  now  removed,  and  the  casts  re- 
adjusted in  their  proper  positions  in  the  base-plates,  when  they  should 
be  fastened  to  the  bite  to  prevent  slipping,  as  represented  in  Fig.  394. 

The  Articulator. — The  object  of  a  bite  is  to  secure  the  proper 
relation  of  the  jaws  for  the  arrangement  of  the  teeth.  Before  ar- 
ranging the  teeth,  means  must  be  provided  for  maintaining  the  casts 
in  their  proper  relation  to  each  other  when  the  wax-bite  is  removed. 
An  instrument  for  this  purpose  is  called  an  articulator,  and  is  illustrated 
in  Fig.  395.  When  such  an  instrument  is  not  at  hand,  a  plaster  articu- 
lator can  be  arranged  by  extending  the  casts  posteriorly,  as  illustrated  in 

Fig.  395. 


Hinge  pm 


Lower  j 
S.  S.  White  articulator. 


Fig.  396.  In  the  latter  illustration  the  wax  has  been  removed  in  order  to 
show  the  relation  of  the  upper  and  lower  ridges,  but  before  the  wax  has 
been  removed,  as  in  Fig.  394,  the  extension  of  plaster  to  form  the  articu- 
lator is  poured  around  the  base  of  the  lower  cast.  After  this  has  hard- 
ened soft  plaster  is  poured  around  the  base  of  the  upper  cast,  allowing  some 
to  fall  upon  the  posterior  extension  of  the  lower  model.  In  Fig.  396  the 
position  of  the  casts  is  shown  within  the  heavy  lines,  while  the  plaster 
extension  is  shown  above,  below,  and  posterior  to  the  lines. 


352 


THE  ''BITE"    OR   OCCLUSION. 


The  joint  at  A  is  to  permit  of  separation  when  desired ;  the  dovetail 
is  to  ensure  a  perfect  readjustment  of  the  two  parts.  This  is  the  simplest 
form  of  articulator,  and,  though  but  little  used,  it  is  still  of  value. 


Fig.  396. 


I.  ouMlkliuliuiH 

Showing  plaster  articulator  v,  ith  wax-bite  removed 

The  form  of  articulator  in  general  use  at  the  present  time  is  illus- 
trated in  Fig.  395.  It  is  made  of  brass,  and  consists  of  an  upper  and 
lower  plate  held  together  by  a  hinge  pin.  The  upper  plate  is  held  at  any 
desired  point  by  a  set-screw,  and  the  upper  and  lower  plates  of  the 
articulator  are  separated  or  lowered  by  the  bite-screw,  A. 

In  mounting  cases  in  this  instrument  the  cast  and  bite,  as  shown  in 
Fig.  394,  are  placed  between  the  two  plates  of  the  articulator,  raising 
the  upper  part  by  the  bite-screw,  A,  so  that  it  will  not  quite  touch  the 
upper  plaster  cast. 

Fig.  397. 


Showing  the  plaster  casts  and  bite  mounted  in  the  anatomical  articulator. 

The  base  of  the  casts  should  be  trimmed  to  a  perfectly  horizontal 
plane,  when  a  thin  batter  of  plaster  is  mixed  and  poured  over  the  lower 
part  of  the  articulator,  and  the  lower  cast  quickly  placed  in  it,  and  the 
plaster  brought  up  around  the  base  of  the  cast  to  fasten  it.     The  upper 


BITES  FOB  FULL  AND  PABTIAL  DENTUBES.  353 

cast  is  fastened  in  the  same  manner  to  the  upper  part  of  the  articulator. 
When  the  plaster  has  hardened  the  bite-wax  can  be  separated  at  the 
occluding  surface  and  prepared  for  the  arrangement  of  the  teeth.  In 
using  this  articulator  it  should  always  be  observed  that  the  bite-screw  is 
opened  a  few  threads  to  permit  of  bringing  the  casts  nearer  each  other 
in  case  the  bite  was  taken  too  long. 

Anatomical  Articulator. — This  articulator  is  shown  in  Fig.  397, 
with  the  same  models  and  bite  as  seen  in  Fig.  394  mounted  in  it.  It  is 
the  invention  of  Dr.  W.  G.  A.  Bonwill.  The  inventor  claims  for  it 
special  advantages,  which  will  be  explained  in  the  section  on  Articulation. 

Bites  for  Full  Upper  or  Lower  Dentures. — To  take  a  bite  for  a 
full  upper  or  lower  denture  a  base-plate  and  bite-wax  are  arranged  after 
the  manner  just  described,  but  in  place  of  an  opposing  bite-plate  of  wax 
there  would  be  the  opposing  teeth,  upper  or  lower,  as  the  case  might  be. 
The  same  rules  for  obtaining  the  length  of  the  teeth,  height  of  lip, 
median  line,  and  contour  are  followed,  but  the  wax-bite  must  be  trimmed 
to  allow  each  of  the  opposing  teeth  to  strike  it  squarely.  The  bite-plate 
is  now  removed  and  the  occluding  surface  warmed  slightly,  when  it  is 
returned  to  the  mouth  and  the  patient  instructed  to  close  against  it.  This 
will  give  an  impression  of  the  points  of  the  opposing  teeth  in  the  oc- 
cluding surface  of  the  wax.  It  is  now  taken  from  the  mouth  and 
returned  to  the  model,  after  which  an  impression  of  the  opposing  teeth 
should  be  taken  and  an  articulating  cast  made. 

This  cast,  when  recovered  from  the  impression,  is  adjusted  in  the 
imprints  of  the  teeth  on  the  occluding  surface  of  the  bite-plate  and 
fastened  with  melted  wax. 

The  bite  and  two  models  are  then  mounted  in  the  articulator  after 
the  manner  described  for  entire  dentures. 

Bites  for  Partial  Dentures. — Any  artificial  denture  requiring  less 
than  the  full  complement  of  teeth  is  called  a  partial  denture.  If  one  or 
two  natural  teeth  only  remain,  the  bite  is  usually  taken  after  the  method 
just  described,  but  openings  should  be  made  in  the  base-plate  to  allow 
the  natural  teeth  to  project  (Fig.  405). 

If  the  case  is  for  one,  two,  or  four  artificial  teeth,  it  is  not  always 
necessary  to  construct  a  base-plate.  If  two  teeth — say  a  central  and 
lateral  incisor — be  absent,  a  roll 

of    soft   wax    should    be    placed  Fig.  398. 

over  the  space,  and  extend  about 
the  width  of  two  teeth  on  either 
side.  The  patient  may  now  bite 
into  this,  and  after  the  wax  has 
been  pressed  close  against  the 
teeth  and  subsequently  cooled  it 
may  be  removed  and  adjusted  in  the 
same  position  on  the  plaster  cast. 
After  the  wax  is  adjusted  the 

cast  should  be  filled  to  a  level  with       showing  upper  cast  a,  bite-wax  CC,  and  lower 

the  cutting  edges  of  the  plasterteeth       antagonizing  cast  b. 

with  a  roll  of  wet  tissue-paper.  A 

sheet  of  wet  tissue-paper  is  now  spread  over  this  and  the  cutting  edges 

of  the  plaster  teeth,  and  as  far  forward  as  the  wax.     The  wax-bite  is 

23 


354 


THE  ''BITE"    OR   OCCLUSION. 


then  filled  in  with  thin  plaster,  which  is  allowed  to  flow  on  the  cutting 
edges  of  the  teeth,  but  not  over  the  sides. 

At  the  posterior  extremity  of  the  east  the  plaster  may  be  allowed  to 
run  down  to  a  level  with  the  base  of  the  cast.  The  paper  which  has 
been  previously  spread  over  the  plaster  cast  will  prevent  the  two  pieces 
from  uniting.  After  the  plaster  has  hardened  the  wax  is  softened  in 
warm  water  and  removed,  when  the  bite  and  upper  cast  may  be  separated. 
(See  Fig.  398.  Bites  for  partial  cases  are  described  later,  "  New  Bite- 
taking  Means  and  Methods.") 

Bites  on  a  Permanent  Base-plate. — Bites  for  S^waged  "Work. — 
Dentures  constructed  with  a  plastic  base,  such  as  vulcanite,  celluloid, 
Watts'  metal,  cast  aluminum,  etc.,  require  an  arrangement  of  the  teeth 
upon  wax  plates  (temporary  base-plates  or  trial  plates).  With  swaged 
plates,  such  as  gold,  silver,  platinum,  etc.,  the  bite  is  taken  and  the  teeth 
arranged  directly  upon  the  permanent  plate. 

After  the  plate  is  swaged,  properly  trimmed,  and  wired  (if  a  wire  is 
necessary),  a  ridge  of  wax  is  placed  directly  upon  the  metal  plate,  and 
built  up  according  to  the  instruction  given  in  the  first  part  of  this  chap- 
ter. The  principles  involved  and  the  method  employed  for  obtaining  a 
bite  with  swaged  work  are  the  same  as  for  vulcanite  or  celluloid,  the  only 
diiference  being  in  the  use  of  the  permanent  metal  plate  instead  of  the 
wax  trial  plate. 

Bites  for  Crown-  and  Bridge-work. — "  Crown-  and  bridge-work  " 
are  methods  of  dental  substitution  which  dispense  with  the  usual  forms 

Fig.  399. 


Showing  the  manner  of  mounting  a  crown  or  small  "bridge." 

of  base-plates.     Some  forms  of  crowns  are  fitted  directly  to  the  root  of 
the  tooth  in  the  mouth,  no  bite  being  necessary. 

The  form  usually  requiring  a  bite  is  known  as  the  ferrule  crown.    In 


DIFFICULTIES  ENCOUNTERED    WHILE  TAKING  BITES.        355 

this  case  the  ferrule  is  first  adjusted  to  the  root,  after  which  a  roll  of 
soft  wax  is  placed  over  it  and  the  adjoining  teeth,  and  the  opposing 
teeth  are  closed  into  it.  After  the  wax  is  chilled  it  is  slipped  off  and 
laid  aside. 

If  the  ferrule  is  detached  from  the  root  with  the  bite,  it  is  recovered 
and  readjusted  to  the  root  and  a  plaster  impression  is  taken.  The 
ferrule  and  post  usually  come  away  with  the  impression,  and  if  not 
they  must  be  removed  from  the  tooth  and  placed  in  the  impression 
and  fastened  in  place. 

The  impression  is  then  filled  with  a  mixture  of  sand  and  plaster  or 
marble-dust  and  plaster  (plaster,  2  parts ;  sand  or  marble-dust,  1  part). 
After  this  cast  has  hardened  the  impression  is  broken  off,  the  surplus 
plaster  trimmed  away,  and  the  base  made  perfectly  flat.  The  bite-wax 
is  now  adjusted  to  the  cast,  and  the  whole  mounted  in  a  crown  articu- 
lator, as  seen  in  Fig.  399,  B. 

Bites  for  small  pieces  of  bridge-work,  where  there  are  only  one  or 
two  spaces  to  be  bridged  over  in  connection  with  the  abutments,  are  taken 
and  mounted  in  essentially  the  same  manner  as  for  a  single  crown. 

In  extensive  pieces  of  bridge-work  the  "  true  bite-plates  "  are  exceed- 
ingly useful,  though  accurate  bites  in  these  cases  may  be  obtained  with- 
out the  use  of  base-plates. 

The  method  for  using  bite-plates  and  of  mounting  the  bite  in  bridge- 
work  is  practically  the  same  as  for  partial  plates,  the  only  difference 
being  that  the  crowns  or  caps  used  as  abutments  for  the  bridge  must  be 
in  position  on  the  natural  teeth  before  the  bite  is  taken. 

If  it  is  desirable  to  have  something  more  resistant  than  plaster  an- 
tagonizing teeth  to  articulate  in  bridge-work,  "  modelling  compound  " 
may  be  used  for  the  bite  instead  of  wax. 

Into  the  modelling  compound  bite  a  fusible  metal,  composed  of  8 
parts  tin,  4  parts  lead,  2  parts  bismuth,  and  2  parts  cadmium,  can  be 
'Cast,  thereby  giving  a  metal  antagonizing  cast  in  place  of  one  of  plaster. 

Difficulties    encountered  while  Taking  Bites. — By  a  careful  ex- 
amination of  the  temporo-maxillary  articulation  the  student  will  observe 
that  the  lower  law  cannot  close  farther  back  than 
the  position  of  occlusion.     Therefore  any  move-  ■^^^-  ^0^- 

ment  of  the  jaw  save  that  of  the  occluding  mo- 
tion must  bring  the  condyles  forward  in  the 
glenoid  fossae. 

When  a  patient  has  lost  all  of  the  teeth  from 
either  jaw  there  is  no  fixed  point  of  occlusion, 
and  the  patient  may  contract  the  habit  of  moving 
the  jaw  about  to  obtain  different  bearings  on  the 
■edentulous  ridges  for  the  purpose  of  mastication. 
If  this  condition  continues,  it  may  become  diffi- 
-cult  to  ascertain  when  the  condyles  are  resting  in 
the  glenoid  fossse,  and  the  patient  is  apt  to  pro- 
trude the  jaw  to  one  side  or  the  other  or  directly 
forward,  when  the  bite  is  being  taken,  and  thus  give  a  false  occlusion.^ 

From  the  fact  that  the  lower  jaw  cannot  be  drawn  back  farther  than 

^  Under  some  conditions  the  shape  and  outlines  of  the  articulating  surfaces  of  the 
maxillary  and  temporal  bones  may  undergo  permanent  alteration. — Ed. 


356  THE  ''BITE"    OR   OCCLUSION. 

the  position  of  occlusion,  any  instruction  given  the  patient,  such  as 
"  bite  back,"  or  "  close  naturally,"  etc.,  will  cause  him  to  attempt  to  close 
in  a  certain  way,  and  he  will  almost  invariably  close  the  wrong  way. 

There  have  been  many  suggestions  as  to  how  this  tendency  to  pro- 
trusion can  be  overcome,  but  few  of  them  seem  to  be  of  any  real  value. 

The  method  which  has  been  found  most  reliable  in  securing  a  correct 
closure  is  to  instruct  the  patient  to  swallow,  and  just  as  the  act  of  swal- 
lowing is  complete  have  him  bite  firmly  until  told  to  relax. 

When  the  patient  has  been  for  some  years  without  teeth,  even  the 
above  method  fails  and  something  more  radical  is  necessary.  A  little 
apparatus,  which  was  invented  by  Dr.  Garretson  of  Iowa,  has  been 
satisfactorily  employed  in  several  cases,  and  is  illustrated  in  Fig.  400» 

It  consists  of  two  steel  strips  about  6  inches  long,  at  one  end  of 
which  are  projections  to  enter  the  external  ear,  and  a  leather  strap  pass- 
ing over  the  occiput  which  prevents  the  ear-pieces  from  slipping  down. 
At  the  other  ends  of  the  metal  strips  is  a  chin  plate  which  works  on  a 
ratchet,  and  which  may  be  moved  forward  or  backward  as  the  case 
requires. 

After  placing  the  ear-pieces  in  position  and  tightening  the  straps, 
the  chin  plate  is  to  be  moved  up  firmly  against  the  chin.  The  patient 
should  now  open  and  close  the  mouth  repeatedly,  and  as  the  lower  jaw 
is  drawn  backward  the  chin  plate  is  moved  upward  until  il:  is  certain 
that  the  condyles  are  at  rest  in  the  glenoid  fossae.  In  this  position  the 
patient  can  open  and  close  the  mouth  comfortably,  but  any  attempt  at 
protrusion  will  meet  with  resistance  by  the  ear-lugs. 

The  bite-plates  are  then  adjusted  and  the  bite  is  taken  as  usual. 
Fig.  400  illustrates  the  application  of  the  instrument. 

The  protrusive  tendency  is  always  increased  by  an  excess  of  bite-wax 
and  by  failure  to  properly  trim  the  wax  base-plates. 

Before  attempting  to  take  the  bite  the  wax  plates  should  be  carefully 
trimmed  to  prevent  them  being  forced  off  the  ridges  by  the  muscles  of 
the  lips  and  cheeks.  The  attachment  of  the  buccinator  muscle  should  be 
especially  observed,  for  if  there  be  any  infringement  upon  this  muscle 
every  attempt  to  open  the  mouth  will  be  accompanied  by  a  displacement 
of  the  base-plates.  The  continual  displacement  of  the  base-plates  causes 
uneasiness  to  the  patient,  and  in  his  or  her  efforts  to  maintain  the  plates 
in  position  the  lower  jaw  is  forced  forward.  The  bite-wax  should  also 
be  trimmed  to  the  smallest  possible  dimensions  that  will  permit  of 
obtaining  the  proper  markings. 

When  the  bite-plates  are  first  inserted  it  is  usual  to  find  them  in  con- 
tact posteriorly  when  the  mouth  is  closed,  and  there  is  a  space  be- 
tween the  occluding  surfaces  anteriorly.  This  indicates  too  great  depth 
to  the  wax  at  the  points  of  contact,  and  the  wax  is  to  be  trimmed  off 
until  there  is  an  even  contact  over  the  entire  occluding  surfaces. 

It  sometimes  happens,  however,  that  the  plates  strike  anteriorly  first, 
and  if  the  cheeks  are  then  drawn  away  with  the  finger  and  the  occluding 
surface  of  the  wax-bite  observed,  it  will  be  found  in  perfect  contact. 

This  is  often  deceptive,  for  there  would  frequently  be  a  space  between 
the  plates  posteriorly  if  they  were  held  in  contact  with  the  ridges.  The 
force  of  occlusion  and  striking  anteriorly  first  caused  a  tilting  at  the 
heel,  which  would  give  the  appearance  of  proper  contact. 


DIFFICULTIES  ENCOUNTERED    WHILE  TAKING  BITES.        357 

If  dentures  were  constructed  after  such  a  bite,  there  would  be  con- 
siderable space  between  the  opposing  bicuspid  and  molar  teeth  when 
placed  in  the  mouth,  and  contact  only  with  the  anterior  teeth. 

When  the  above  condition  occurs,  it  is  well  to  hold  the  base- plates 
against  the  ridges  firmly  with  the  fingers,  and  then  instruct  the  patient 
to  close  the  mouth  two  or  three  times  gently ;  the  space  can  then  be 
detected  and  the  proper  remedy  applied-. 

Another  annoying  occurrence  when  taking  a  bite  with  base-plates  of 
wax  is  the  spreading  of  the  base-plate  under  the  force  of  occlusion.^ 
This  is  more  perceptible  when  taking  a  bite  for  a  full  upper  denture  with 
opposing  natural  teeth. 

Some  operators,  instead  of  taking  a  bite  for  full  upper  dentures  as 
described  in  this  chapter,  place  a  roll  of  soft  wax  on  the  occluding  sur- 
face of  the  bite-plate,  and  have  the  patient  close  into  this  with  his  teeth, . 
thereby  taking  the  bite  and  an  impression  qf  the  opposing  teeth  at  the 
same  time. 

The  warm  wax,  together  with  the  heat  of  the  mouth,  causes  a  soften- 
ing of  the  base-plate,  and  under  the  force  of  occlusion  the  latter  spreads. 

When  the  bite  and  base-plate  are  returned  to  the  cast,  it  is  found 
that  the  palatine  portion  of  the  base-plate  is  not  in  contact  with  the  cast. 
The  operator  often  attempts  a  readaptation  of  this  part  of  the  plate  by 
pressing  it  down,  and  in  doing  so  draws  the  impression  of  the  occluding 
teeth  nearer  the  centre  of  the  mouth. 

When  the  denture  is  finished  the  articulation  of  the  artificial  teeth 
with  the  natural  is  quite  diiferent  from  their  arrangement  on  the 
articulator. 

The  deficiency  may  not  be  so  great  as  to  require  a  complete  recon- 
struction of  the  denture,  but  the  use  of  the  corundum  wheel  will  be 
necessary  to  partially  correct  it,  whereas  a  little  more  time  and  care 
expended  while  taking  the  bite  would  have  afforded  more  accurate 
results. 

jSTo  matter  how  much  time  is  spent  in  taking  a  bite  with  wax  base- 
plates, there  always  follows  a  slight  deficiency  in  the  articulation. 

It  is  impossible  to  so  closely  adapt  wax  or  paraffin  base-plates  to  the 
cast  that  there  will  not  be  some  discrepancy  between  the  model  and  the 
base-plates.  When  such  is  the  case  the  position  of  the  base-plate  in 
the  mouth  may  be  slightly  different  from  its  position  on  the  model. 

This  is  another  cause  for  the  difference  between  the  occlusion  in  the 
mouth  and  that  of  the  articulator,  and  even  in  entire  dentures  the  use 
of  the  corundum  wheel  is  often  necessary  before  precision  of  occlusion 
is  obtained. 

Dr.  W.  S.  How  described  "  New  Bite-taking  Means  and  Methods, 
with  illustrations  of  the  use  of  bite-plates,"  in  the  Dental  Cosmos  for 
Sept.  and  Oct.,  1894,  which  the  author  deems  of  much  value. 

In  Fig.  401  is  seen  an  upper  bite-plate  of  suitable  thin  metal, 
having  a  palatal  portion  A,  a  plane  portion  B,  and  a  contoured  edge  or 
border  C.  When  a  full  upper  denture  is  contemplated,  the  bite  is  at 
once  taken  by  placing  on  the  bite-plate  (Fig.  401)  a  sufficient  quantity 
of  warmed  beeswax  to  secure  a  completely  good  impression,  and  at  the 

'  To  avoid  this  difficulty  many  operators  prefer  swaged  temporary  base-plates  of  the 
metal  commonly  used  for  the  formation  of  chambers  in  vulcanite  and  celluloid  Avork. — Ed. 


358 


THE  ''BITE"    OR    OCCLUSION. 


same  time  afford  material  for  modelling  the  labial  and  buccal  surfaces  in 
a  suitable  manner  to  produce  the  proper  facial  expression. 


Fig.  401. 


The  bite-plate  here  exhibits  its  novel  and  useful  functions  in  enabling 
the  operator  to  readily  lengthen  or  shorten  the  bite,  and  also  adapt  the 
bite-plane  B  to  the  lip-line,  as  well  as  to  the  occluding  lower  teeth. 
When  this  has  been  carefully  done  and  the  mass  removed  from  the 
mouth,  the  appearance  will  approximate  that  of  Fig.  402.     If  the  bite 


Fig.  402. 


then  requires  an  increase  of  length,  the  bite-plate  is  held  a  moment  over 
the  Bunsen  flame,  when  it  will  fall  on  a  paper  napkin  held  in  the  hand. 
It  is  then  covered  with  a  thin  sheet  of  wax,  replaced  on  the  modelled 
wax,  trimmed  with  the  wax-knife  along  the  contour  border  C,  again  put 
in  the  mouth,  and  comfortably  remodelled  and  adjusted.  The  quickly 
transmitted  heat  of  the  metal  bite-plate  permits  facile  changes  in 
occlusive  adaptation  and  contour,  without  disturbance  of  the  fit  of  the 
impression  portion  of  the  wax — an  advantage  of  real  consequence  and 
value. 

If  upon  further  study  it  is  desired  to  shorten  the  bite,  the  mass  is 
removed  from  the  mouth,  the  plate  quickly  warmed  over  the  Bunsen 
flame,  all  replaced  in  the  mouth,  and  the  patient  instructed  to  close  the 
teeth  firmly  on  the  bite-plate,  which,  while  accurately  maintaining  the 
plane  of  the  occluding  teeth  to  which  it  has  been  conformed,  will  at  the 
same  time  cause  the  softer  wax  immediately  in  contact  with  the  plate  to 
gradually  yield  until  the  bite  becomes  suitably  shortened. 

In  this  connection  it  is  important  to  note  the  functional  difference  of 
this  metal  bite-plate  from  the  common  wax  plate,  which  yields  and  is 
indented  by  any  considerable  pressure  of  the  occluding  teeth  ;  whereas 
in  the  present  instance  so  soon  as  the  wax  has  cooled  to  a  slight  stiffness 
the  patient  is  directed  to  press  the  teeth  hard  on  the  bite-plate  (see  Fig. 


DIFFICULTIES  ENCOUNTERED    WHILE  TAKING   BITES. 


359 


403),  and  the  result  is  a  bite-gauge  identical  in  length  with  that  which 
the  finished  denture  will  have  under  the  ordinary  pressure  of  the  closed 
jaws.  Many  of  the  usual  disappointing  discrepancies  between  the 
common  soft  wax-bite  gauges  and  the  resulting  defectively  articulating 
dentures  may  now  be  avoided. 


Fig.  403. 


Fig.  404. 


The  smooth  and  hard  surface  of  the  bite-plane  B  fixes  a  constant 
and  firm  limit  to  the  bite-length,  while  allowing  the  utmost  freedom  of 
lower-jaw  movement  in  occlusion  during  the  adjusting  and  modelling 
])rocesses  to  secure  a  natural  oral  and  facial  expression,  with  a  proper 
lip  line,  as  indicated  in  Fig.  404.  This  having  been  accomplished,  a 
roll  of  warmed  wax  is  placed  on  the  under  side  of  the  bite-plate,  which 
is  replaced  in  the  mouth,  and  the  patient  while  the  previous  process  was 
going  on  having  been  instructed  and  practised  in  the  correct  manner  of 
closing  the  jaw,  the  head  being  thrown  back  to  bring  the  face  horizontal 
and  the  jaw  held  as  far  back  as  possible,  the  teeth  are  pressed  through 
the  wax  on  to  the  bite-plate,  and  kept  there  while  with  the  finger  the 
labial  and  buccal  portions  of  the  soft  wax  are  pressed  in  upon  the 
natural  teeth.  The  mass  is  then  carefully  removed  from  the  mouth  and 
kept  in  safe  readiness  for  transfer  to  the  plaster  model  when  obtained 
from  the  plaster  impression ;  and  it  is  unnecessary  to  dwell  upon  the 
advantages  of  securing  a  certainly  correct  bite  at  the  time  of  the  sitting 
secured  for  taking  the  plaster  impression.  Fig.  403  shows  a  bite  thus 
taken  and  transferred  to  the  cast  set  in  an  articulator,  and  represents 
also  the  correct  bite  so  obtained.  This  novel  bite-plate  provides  for  the 
taking  of  a  very  short  bite.  In  fact,  the  bite-plane  B  may  rest  directly 
upon  the  gums,  and  the  under  teeth  strike  the  plate,  yet  the  rigidity  of 
the  metal  plate  is  such  that  the  wax  impression  and  modelling  will  not 
warp  in  the  adjusting,  shaping,  and  removing  manipulations ;  whereas 
by  the  old  mere  wax  methods  a  trustworthy  very  short  bite  is  often 
almost  impossible. 

For  partial  upper  dentures  sections  of  the  bite-plate  are  with  plate- 
nippers  cut  out  as  at  EE  (Fig.  405),  and  the  bite  taken  in  the  way 
previously  described. 

The  lower  bite-plate  (Fig.  406)  is  of  like  character  with  that  of  Fig. 
401,  the  lingual  portion  D  being  designed  to  approximate  the  lingual 
conformation   of  the  lower  jaw,  while  the  bite-plane  B  and   contour 


360 


THE  "BITE"    OB   OCCLUSION. 


border  C  have  the  bite-taking  functions  of  the  upper  bite-plate.     For 
partial  lower  dentures  sections  may  be  cut  out  as  at  EEF  (Fig.  405),  to 


Fig.  405. 


Fig.  406. 


permit  the  passage  of  the  remaining  natural  teeth  through  the  bite-plate, 
the  intermediate  planes  of  which  can  be  shaped  to  conform  to  any  plane 
of  the  occluding  upper  tooth  or  teeth. 

The  Separation  of  Bites. — After  the  plaster  which  fastens  the  bite 
to  the  articulator  has  hardened  the  bite  should  be  separated  at  the 
occluding  surface.  This  is  accomplished  in  entire  cases  by  passing  a 
heated  spatula  or  thin  knife-blade  between  the  occluding  surfaces,  when 
they  will  readily  part. 

To  separate  partial  cases  or  full  upper  or  lower  cases  where  there  are 
opposing  plaster  teeth,  the  bite-wax  containing  the  plaster  antagonizing 
teeth  is  to  be  warmed  until  the  bite-wax  is  softened  throughout.  The 
models  may  then  be  readily  separated  and  all  surplus  wax  removed. 


Articulation. 

The  articulation  of  the  teeth  is  one  of  the  most  important  steps  in  the 
process  of  constructing  an  artificial  denture. 

By  the  term  "  articulation  "  is  meant  the  placing  or  an  arrangement 
of  the  artificial  teeth  upon  base-plates,  so  that  they  will  appear  like,  and 
perform  as  nearly  as  possible  the  functions  of,  the  natural  teeth  for  which 
they  are  a  substitute. 

It  has  been  often  observed  that  under  most  conditions  the  more  closely 
is  followed  the  normal  arrangement  or  articulation  of  the  natural  teeth 
the  greater  will  be  the  utility  of  the  artificial. 

Therefore,  it  is  of  first  importance  for  the  student  to  study  the  teeth, 
their  names,  forms,  arrangement,  and  requirements,  in  order  to  apply 
the  principles  in  constructing  an  artificial  denture. 

Names,  Shape,  Surfaces,  and  Position  of  Teeth. — The  permanent 
teeth  are  thirty-two  in  number,  sixteen  in  either  jaw,  divided  as  follows  : 


Upper  or  f    j 
Superior.  \ 


Central 
incisors. 

2 


Lateral 

incisors. 

2 


Cuspids. 
2 


Bicuspids. 
4 


Molars. 
6 


Lower  or  f  „  -^  , 
Inferior  "1  .Central 
Aiueiiui.    (.     incisors. 


2 

Lateral 
incisors. 


2 
Cuspids. 


The  arrangement  is  bilaterally  symmetrical. 


4 

Bicuspids. 


6 

Molars. 


DIFFERENTIATION  OF  THE  TEETH. 


361 


Taking  a  perpendicular  line  through  the  centre  of  the  face,  it  should 
fall  between  the  central  incisor  teeth  superior  and  inferior. 

Beginning  at  this  line  and  counting  either  way,  we  have  in  order — 
first,  the  central  incisor ;  second,  the  lateral  incisor ;  third,  cuspid ; 
fourth,  first  bicuspid  ;  fifth,  second  bicuspid ;  sixth,  first  molar ;  seventh, 
second  molar  ;  eighth,  third  molar. 

For  the  purposes  of  an  artificial  denture  twenty-eight  teeth  are 
found  sufficient,  the  third  molars  being  omitted  (Fig.  407). 


54  3  21123  4  5 

Upper  and  lower  plain  teeth  in  sets  of  twenty-eight. 


Each  tooth  has  five  surfaces,  as  follo:ffiB-r'^ 

1.  Labial  surface,  next  the  lips  or 
Buccal  surface,  next  the  cheeks. 

2.  Incisal  surface,  cutting  edge  of  the  incisor  teeth,  or 

Occlusal  surface,  cutting  or  grinding  surface  of  the  bicuspids  and 
molars. 

3.  Mesial  surface,  the  proximal  surface  directed  toward  the  median  line 

of  the  face. 

4.  Distal  surface,  the  proximal  surface  directed  away  from  the  median 

line  of  the  face. 

5.  Lingual  surface,  next  the  tongue. 

Mesial,  distal,  and  lingual  surfaces  are  common  to  all  the  teeth,  whether 
upper  or  lower. 

The  line  of  junction  between  the  crown  and  root  of  a  tooth  is  called 
the  cervical  portion,  or  "  neck,"  of  the  tooth,  and  is  usually  at  the  gum 
margin. 

In  dental  prosthesis  there  is  use  for  only  the  crowns  of  teeth,  and, 
as  artificial  crowns  are  made  so  nearly  like  the  natural  in  outward 
appearance,  it  is  deemed  advisable  to  use  them  in  the  further  illustration 
of  this  subject. 


Differentiation  op  the  Teeth. 

Upper  Teeth. — In  Fig.  408  are  represented  the  half  of  an  upper  and 
a  low^er  set  of  teeth  for  the  same  mouth,  showing  the  labial  and  buccal 
surfaces  1  to  7  and  a  to  G,  and  the  occlusal  surfaces  of  the  bicuspids 
and  molars,  0.  The  perpendicular  line  represents  the  median  line 
of  the  face.     No.  1  is  the  left  superior  central  incisor.     It  is  recognized 


362 


THE  "BITE"    OB   OCCLUSION. 


as  a  "  broad,  wedge-shaped  tooth,  and  is  the  largest  of  this  style  in  the 
mouth." 

No.  2  represents  the  superior  lateral  incisor  of  the  same  general  form, 
but  smaller.  The  side  to  which  these  teeth  belong  is  determined  by 
looking  at  the  labial  surface  and  placing  the  longer  mesial  surface  M 


Fig.  408. 


T    M       N 


iyiy'tJt/uit_^i  tJ' 

\a\B      CD      E    \     F    \      G 


M 


N 


M         N 


X 
W    1 


10 


11 


U     V 


U       ir 


toward  the  median  line.  Also,  the  more  acute  angle,  where  the  mesial 
surface  31  joins  the  incisal  surface  /,  points  toward  the  median  line  of 
the  face.  N  is  the  distal  surface  of  the  central,  and  points  toward  the 
mesial  surface  of  the  lateral  incisor. 

No.  3  is  the  cuspid,  so  called  from  its  having  a  "  pointed  projection  or 
cusp  on  the  cutting  edge."  The  labial  surface  of  this  tooth  is  convex, 
while  that  of  the  incisors  is  flattened.  The  cusp  has  a  long  and  a  short 
cutting  edge.  K  marks  the  point  of  the  cusp,  J  the  shorter  anterior 
cutting  edge,  and  R  the  distal  and  longer  cutting  edge.  The  mesial  sur- 
face points  toward  the  distal  surface  of  the  lateral  incisor.  Placing  the 
longer  proximal  surface  and  the  shorter  cutting  edge  of  the  cusp  toward 
the  median  line  determines  to  which  side  the  tooth  belongs. 

Nos.  4  and  5  show  the  buccal  surfaces  of  the  first  and  second  bicuspid 
teeth,  which  so  nearly  resemble  the  labial  surface  of  the  cuspid,  except  they 
are  smaller,  that  no  further  description  of  these  surfaces  is  necessary. 
In  addition  to  the  labial  cusp  these  teeth  have  a  lingual  cusp,  shown  in 


ARTIFICIAL   TEETH.  363 

vertical  section  Nos.  8  and  9,  U.     The  lingual  cusp  is  usually  a  little 
shorter  than  the  buccal  cusp  V,  and  not  so  pointed. 

The  superior  molars  are  the  grinding  teeth,  and  have  "  broad  occlud- 
ing surfaces,  possessing  four  cusps,"  Nos.  6  and  7,  0,  the  two  anterior  or 
mesial  cusps  being  heavier  and  longer  than  the  two  distal  cusps,  while 
the  mesio-buccal  angle  is  the  most  acute.  Directing  the  broader  proxi- 
mal surface,  while  looking  at  the  buccal  surface,  toward  the  median  line 
of  the  face,  will  determine  to  which  side  the  tooth  belongs. 

The  second  molar  7  very  nearly  resembles  the  first  molar,  except  being 
a  little  smaller. 

Lo^wer  Teeth. — While  the  superior  central  incisor  is  the  largest 
wedge-shaped  tooth  in  the  mouth,  the  inferior  central  incisor  is  the 
smallest,  and  is  shown  in  A.  It  has  the  same  general  formation  as  the 
superior  central,  but  is  longer  in  proportion  to  breadth. 

The  inferior  lateral  incisor  5  is  a  little  broader  than  the  inferior  cen- 
tral, and  the  crown  is  usually  a  little  shorter. 

The  inferior  cuspid  C  bears  a  close  resemblance  to  the  superior  cus- 
pid, but   is  longer  in  proportion  to  breadth. 

The  first  inferior  bicuspid  D  resembles  the  inferior  cuspid  in  form 
more  than  a  bicuspid,  but,  owing  to  its  extreme  narrowness,  it  would 
never  be  mistaken  for  a  cuspid.  It  ^qry  seldom  possesses  more  than  a 
diminutive  lingual  cusp,  as  shown  in  Fig.  $08,  W,  and  is  much  narrower 
than  the  second  bicuspid  inferior.  Bicuspid,  second  inferior,  is  broader 
than  the  first  bicuspid,  and  in  proportion  to  length  is  broader  than  the 
upper  bicuspids.  The  principal  distinguishing  feature  of  this  tooth  is  its 
lingual  cusp,  No.  11,  Y,  which  is  usually  more  acute  than  the  buccal  cusp 
Z,  and  quite  as  long;  the  lingual  cusp  is  divided  into  two  distinct  sections, 
mesial  and  distal.     The  lingual  surface  is  quite  as  broad  as  the  buccal. 

Molar,  first  inferior,  is  the  largest  tooth  in  the  lower  jaw,  is  "  trape- 
zoidal in  form,  has  five  cusps,"  three  buccal  and  two  lingual,  F  and 
O,  the  lingual  cusps  beings  usually  quite  as  long,  and  often  a  little 
longer  than  the  buccal  cusps.  The  upper  molar  is  more  rhombic  in 
form,  and  has  four  cusps,  the  two  lingual  being  slightly  shorter.^  The 
side  to  which  it  belongs  is  determined  by  the  same  rule  as  with  the 
upper  molars. 

Molar,  second  inferior,  has  the  general  shape  of  the  first,  but  is 
smaller  and  possesses  but  four  cusps,  G  and  0. 

The  same  rules  are  applied  for  determining  the  side  of  the  mouth 
to  which  the  lower  teeth  belong  as  with  the  upper.  A  careful  study  of 
the  anatomy  of  the  natural  teeth,  as  found  in  Black's  Dental  Anatomy, 
where  the  foregoing  facts  are  treated  more  elaborately  than  is  admissible 
in  a  chapter  of  this  character,  will  be  of  great  service  to  the  student  of 
prosthetic  dentistry. 

Artificial  Teeth. 

Artificial  teeth  are  divided  into  two  general  classes — viz.  gum  teeth 
and  plain  teeth. 

^  Observation  has  shown  that  when  the  lingual  cusps  of  lower  molars  are  longer  than 
the  buccal  (of  natural  teeth)  there  is  a  corresponding  diminution  in  the  length  of  the 
lingual  cusps  of  upper  molars,  these  being  just  as  much  shorter  than  their  buccal  as  the 
lingual  cusps  of  molars  are  longer  than  their  buccal  cusps. 


364 


THE  ''BITE"    OR   OCCLUSION. 


These  are  again  subdivided  into  several  varieties,  as  follows  (see  Figs. 
409-417) : 

Fig.  410.  Fig.  411. 


Fig.  412. 


Fig.  413. 


Fig.  414. 


Fig.  415. 


Gum 
Teeth. 


Plain 
Teeth. 


Fig.  416. 


Single  gum  teeth,  Fig.  409. 
Gum  sections,  Fig.  410. 
j   Festooned  gum  sections.  Fig.  411. 
1^  Gum  teeth  for  metal  plates  (gum  plate-teeth).  Fig.  412. 
'  Are  always  single,  Figs.  413,  414,  415,  416,  417. 
For  mental  plates  (plain  plate-teeth).  Fig.  416. 
For  vulcanite  plates.  Figs.  413,  414. 
1   For  celluloid  plates,  Figs.  413,  414. 

For  continuous-gum  plates.  Fig.  417. 
1^  Countersunk-pin  teeth.  Fig.  415. 
The  teeth  are  again  divided  into  "  long  bite  "  and  "  short  bite,"  com- 
mon to  both  gum  and  plain  teeth. 

While  the  labial  and  proximal  surfaces  of  artificial  teeth  resemble  the 
natural  organs,  the  lingual  side  is  adapted  for  attachment  to  the  base-plate 
of  the  denture.  In  this  side  two  or  more  platinum  pins  are  arranged, 
the  position  of  which  determines  the  length  of  the  bite,  whether  long  or 


RULES  FOR  SELECTING   TEETH. 


365 


short,  and  is  a  very  important  matter  to  consider  in  making  a  proper 
selection. 

In  addition  to  the  divisions  of  artificial  teeth  already  given,  there 
are — 

Teeth  with  headed  pins,  Figs.  410,  413,  414,  415,  for  plastic  bases. 

Teeth  with  straight  pins.  Figs.  412,  416,  for  plate  work. 

Teeth  with  pins  lengthwise,  Figs.  412,  416. 

Teeth  with  pins  crosswise.  Figs.  413,  414. 

Pins  lengthwise  are  arranged  in  series  with  the  long  diameter  of  the 
tooth,  or  w^ith  one  pin  near  the  cutting  edge  and  the  other  nearer  the 
neck  of  the  tooth. 

Pins  crosswise  are  arranged  in  parallel  across  the  shorter  diameter  of 
the  tooth.  Short-bite  teeth  usually  have  the  pins  arranged  crosswise,  as 
have  also  gum-section  teeth,  while  in  plain  teeth  the  pins  are  arranged 
either  way. 

Rules  for  Selecting  Teeth. 

In  making  a  selection  of  gum  or  plain  teeth,  long-  or  "  short-bite  " 
teeth,  some  rules  should  be  adopted  on  which  to  base  our  choice. 

By  referring  to  Fig.  418,  No.  1,  we  see  represented  a  vertical  sec- 
tion of  the  ridge  at  the  median  line,  showing  the  position  of  the  upper 

Fig.  418. 


lip  B  at  rest,  and  the  same  at  C  elevated  to  its  highest  point,  as  in 
laughing.  The  space  between  C  and  B  must  either  be  filled  in  with  a 
plain  tooth  or  gum  section.  If  the  distance  between  Cand  B  would 
not  require  a  tooth  too  long  for  the  proper  appearance,  a  plain  tooth 
would  be  suggested,  as  is  seen  in  the  figure. 

The  second  point  to  be  observed  in  this  same  case  is  the  "  bite  "  of 
the  tooth.    In  the  illustration  we  find  the  pins  on  the  lingual  side  nearer. 


366  THE  "BITE"    OR   OCCLUSION. 

the  cutting  edge,  and  the  major  portion  of  the  tooth  extends  above  the 
pins  ;  and  it  is  at  once  recognized  as  a  short-bite  tooth.  It  is  obvious 
that  a  tooth  with  a  longer  cutting  edge  could  not  be  used,  because  it 
would  project  too  far  below  the  lip  line,  B,  and  would  expose  too  much 
tooth.  Again,  if  the  tooth  did  not  extend  as  high  as  A,  the  base  of  the 
denture  would  be  exposed  and  an  unsightly  appliance  would  be  the  result. 

Rule. — A  long  ridge  and  short  lip  suggests  the  use  of  short-bite 
teeth. 

No.  2  illustrates  a  case  w^here  a  plain  tooth  is  indicated,  but  where  a 
short-bite  tooth  is  contraindicated.  The  lip  B  is  longer  and  the  elevation, 
A,  not  so  great  as  in  No.  1. 

As  for  appearance,  a  short  bite-tooth  could  be  used,  but  by  removing 
the  pins  so  far  from  the  ridge  in  order  to  bring  the  cutting  edge  of  the 
tooth  to  the  lip  line  B  an  unusual  thickness  of  the  plate  is  occasioned, 
which  would  be  a  serious  impediment  to  the  tongue  in  speaking.  There- 
fore we  must  use  a  tooth  witli  the  pins  nearer  the  cervical  extremity,  and 
with  the  major  portion  of  the  tooth  between  the  pins  and  cutting  edge. 
This  tooth  will  be  recognized  as  a  long-bite  tooth,  and  is  illustrated  in 
No.  3.  It  will  be  seen  that  the  ridge  lap  is  shorter  than  in  No.  1,  for 
the  reason  that  it  is  not  necessary  for  the  tooth  to  extend  beyond  the 
high  lip  line  A. 

This  character  of  tooth  gives  more  room  for  the  tongue,  and  also 
allows  the  lower  teeth  the  normal  under  bite. 

Rule. — A  short  ridge  and  long  lip  usually  indicate  long-bite  teeth. 

No.  4  illustrates  a  case  where  a  plain  tooth  is  contraindicated,  but 
where  a  long-bite  tooth  is  indicated.  The  lip  line  is  the  same  as  in 
No.  3,  but  it  will  be  noticed  that  the  high  lip  line  is  considerably  ele- 
vated, and  is  as  much  higher  than  No.  3  as  from  C  to  A  in  No.  4.  It 
is  evident  that  the  space  from  ^  to  -B  must  be  filled  in,  either  with  a 
tooth  or  a  tooth  with  porcelain  gum,  but  in  this  case  the  distance  from 
A  to  B  would  give  a  tooth  of  too  great  length  for  a  natural  appearance. 
Therefore  we  must  select  a  gum  section  that  will  give  a  tooth  of  the 
proper  dimensions,  but  with  a  porcelain  gum  extension  that  will  reach 
A,  as  shown  in  No.  5  (known  as  long-bite  gum  tooth). 

Rule. — Where  the  distance  between  the  lip  line  and  high,  lip  line 
would  require  a  tooth  of  too  great  length  for  proper  appearance,  a  "  gum 
tooth  "  is  indicated. 

In  No.  5  the  length  of  tooth  is  shown  to  extend  from  B  to  C,  and 
the  extension  above  C  to  A  is  of  porcelain,  in  order  to  hide  the  unnatural 
base  of  the  denture. 

No.  6  illustrates  the  use  of  a  short-bite  gum  tooth.  This  figure  is 
the  same  as  No.  1,  except  the  high  lip  line  is  at  A  instead  of  C.  It 
will  be  noticed  now  that  the  distance  between  A  and  B  would  require  a 
tooth  too  long  for  a  good  appearance,  as  shown  in  No.  1,  A  to  B  ;  con- 
sequently we  must  reduce  the  size  of  the  tooth  and  add  a  porcelain  gum, 
as  seen  in  No.  6. 

No.  7  illustrates  a  case  where  a  gum  tooth  is  contraindicated.  Owing 
to  the  excessive  fulness  of  the  alveolar  ridge,  the  use  of  a  gum  tooth 
would  cause  an  unnatural  protrusion  to  the  upper  lip,  and,  if  the  same 
method  were  followed  in  the  construction  of  a  denture  in  this  case  as  in 
the  preceding  illustration,  a  plain  tooth  would  also  be  contraindicated. 


RULES  FOR  SELECTING   TEETH. 


367 


In  this  case,  however,  a  plain  tooth  is  indicated  in  order  to  prevent  dis- 
figurement of  the  face,  but  an  entirely  different  method  of  arrangement, 
as  illustrated  in  No.  8. 

The  six  or  eight  anterior  teeth  must  be  arranged  to  rest  with  their 
necks  slightly  imbedded  in  the  gum-tissue  covering  of  the  ridge. 

In  order  to  accomplish  this  the  gum  lap  must  be  ground  thin,  and 
where  this  strikes  the  plaster  cast  the  latter  must  be  trimmed  away 
slightly,  as  shown  in  No.  8. 

When  the  denture  is  inserted  the  front  teeth  press  into  the  gum-tissue 
gently  and  hide  the  cervical  portion  of  the  teeth,  thus  affording  a  very 
close  imitation  of  the  natural  organs. 

No.  8  also  illustrates  another  character  of  tooth — viz.  a  medium  bite, 
the  pins  being  arranged  near  the  centre  of  the  tooth. 

The  same  arrangement  of  teeth  is  necessary  for  No.  7,  A,  No.  8, 
except  that  a  short-bite  tooth  is  suggested. 

No.  9  illustrates  a  case  of  almost  complete  resorption  of  the  ridge. 
In  this  case  a  plain  tooth  could  be  used,  but,  owing  to  the  considerable 
amount  of  vulcanite  necessary  to  restore  the  features,  and  the  danger  of 
not  obtaining  a  good  adaptation  when  so  much  vulcanite  is  used,  it  is 
better  to  use  a  thick  gum  section  in  order  to  reduce  the  quantity  of 
vulcanite. 

Therefore,  as  a  rule  with  vulcanite  base  in  cases  of  great  resorption 
of  ridge  a  thick  gum  section  is  indicated. 

With  a  close  study  of  the  foregoing  illustrations,  and  the  following 
chart  ^  the  student  should  be  able  to  enter  upon  the  study  of  the  more 
artistic  features  of  the  subject. 

Definition  and  Illustration  of  Terms  employed  to  Express  "Va- 
rieties of  Styles  of  Teeth.— Figs.  419-426.  Short  or  Long  Ridge 
Lap. — The  form  of  the  heel  or  butt  of  the  tooth.     Short  or  Long  Shut. 


Fig.  419. 


Fig.  420. 


Fig.  421. 


Short  ridge  lap. 
Long  shut. 
Long  bite. 


Long  ridge  lap. 
Short  shut. 
Short  bite. 


Short  ridge  lap. 
Long  shut. 
Short  bite. 


— The  distance  between  the  upper  and  lower  maxillae  when  the  mouth  is 
naturally  closed.  Shoi^t  or  Long  Bite. — The  extent  of  the  lap  of  the  upper 
tooth  over  the  lower.  Shoulder  Bite. — The  striking  of  the  occluding 
teeth  upon  a  shoulder.     Flat-faced  Teeth. — Those  intended  for  cases  of 

^  Kindly  loaned  by  S.  S.  W.  Dental  Manufacturing  Co. 


368 


THE  "BITE"    OR   OCCLUSION. 


protruding  upper  jaw.     Bow-faced  Teeth. — Those  intended  for  cases  of 
protruding  lower  jaw. 

The  vertical  lines  represent  the  facial  line. 

The  two  horizontal  lines  represent  the  lip  line  in  laughing. 

The  following  cuts  illustrate  what  is  meant : 


Fig.  422. 


Fig.  423. 


Fig.  424. 


Short  ridge  lap. 
Short  shut. 
Short  bite. 


Long  ridge  lap. 
Short  shut. 
Long  bite. 


Long  ridge  lap. 
Short  shut. 
Short  bite. 


Fig.  425. 


Fig.  426. 


Flat-faced  tooth 
for  protruding 
jaw. 


Bow-faced  tooth  for  pro- 
truding lower  jaw. 


Occlusion  and  Articulation. 

The  teeth  are  arranged  in  the  alveolar  process  in  the  shape  of  a 
parabola :  with  the  long  axis  passing  between  the  central  incisor  teeth, 
the' arch  is  a  little  larger  in  the  superior  than  the  inferior  jaw  (Fig.  — ~). 

They  are  also  so  arranged  that  when  the  mouth  is  closed  naturally 
they  will  strike  against  the  opposing  teeth  in  a  definite  manner,  as  shown 
in  Fig.  427.    When  in  this  position  the  teeth  are  said  to  be  in  occlusion. 

During  occlusion  all  of  the  superior  teeth  overlap  the  lower ;  the  six 
anterior  teeth,  superior,  pass  over  and  cover  part  of  the  labial  surface  of 
the  six  inferior  teeth  ;  while  in  the  buccal  region  the  buccal  cusps  of  the 
superior  bicuspids  and  molars  cover  to  a  decreasing  extent  the  buccal 
cusps  of  the  inferior  bicuspids  and  molars. 


OCCLUSION  AND  ARTICULATION. 


369 


This  arrangement  makes  the  upper  arch  a  little  more  prominent  and 
larger  than  the  lower  arch.  It  will  also  be  observed,  by  referring  to 
Fig.  427,  that  with  but  two  exceptions  each  tooth  strikes  against  two 
opposing  teeth,  the  exceptions  being  the  inferior  central  incisor,  which  is 


Fig.  427. 


covered  entirely  by  the  superior  central  incisor,  and  the  last  superior 
molar,  which  covers  about  one-half  or  one-third  of  the  last  inferior 
molar. 

Beginning  at  the  superior  central  incisor,  it  will  be  observed  that  it 
covers  not  only  the  inferior  central,  but  also  about  one-third  to  one-half  of 
the  inferior  lateral  incisor.  The  superior  lateral  covers  the  remaining 
portion  of  the  inferior  lateral  and  about  one-half  of  the  inferior  cuspid. 
The  superior  cuspid  covers  the  remaining  portion  of  the  inferior  cuspid 
and  nearly  half  of  the  first  inferior  bicuspid. 

It  will  be  seen  by  this  arrangement  that  the  inferior  central,  lateral, 
and  cuspid  occupy  a  position  anterior  to  the  point  of  the  cusp  of  the 
superior  cuspid — a  fact  which  it  is  well  to  remember  in  the  selection  of 
entire  sets  of  teeth,  as  it  fixes  the  relative  size  of  the  six  lower  to  the 
upper  teeth. 

By  referring  to  Fig.  427  it  will  be  observed  that  the  first  bicuspid, 
superior,  covers  the  remaining  portion  of  the  first  inferior  bicuspid,  and 
also  about  one-half  of  the  second  inferior  bicuspid.  This  brings  the 
point  of  the  buccal  cusp  of  the  first  superior  bicuspid  between  the 
inferior  bicuspids.  The  manner  of  occlusion  of  the  remainder  of  the 
teeth  is  clearly  shown  in  Fig.  427,  and  needs  no  further  description  here. 

When  the  teeth  in  occlusion  strike  as  shown  in  Fig.  427,  they  are  said 
to  represent  a  normal  articulation. 

Articulation. — The  means  for  properly  masticating  the  food  infers  a 
perfect  articulation  of  the  teeth,  not  only  during  occlusion  of  the  jaws, 

24 


370  THE  ''BITE"    OR   OCCLUSION. 

but  also  during  the  various  movements  of  the  lower  jaw  in  the  acts  of 
incising  and  grinding  the  food. 

The  lower  jaw  is  endowed  with  certain  movements  by  the  muscles 
of  mastication  whereby  the  teeth  are  brought  into  various  relations  with 
each  other  for  the  purpose  of  incising  the  food  when  both  condyles  of 
the  lower  jaw  move  forward  and  downward  in  the  glenoid  fossae,  bringing 
the  cutting  edges  of  the  incisor  teeth  opposite  each  other  for  the  purpose 
of  separating  a  small  portion  of  food  from  the  main  bulk,  prior  to  the 
process  of  mastication. 

During  mastication,  instead  of  both  condyles  moving,  one  condyle 
only  moves  forward  and  downward  in  the  glenoid  fossa,  protruding  the 
lower  jaw  to  one  side  or  the  other.  This  lateral  protrusion,  followed  by 
a  drawing  back  into  the  position  of  occlusion,  is  a  provision  whereby  the 
cusps  of  the  bicuspids  and  molar  teeth,  if  they  are  in  proper  relation  to 
each  other,  can  be  utilized  for  the  comminution  of  the  food. 

It  is  a  fact  that,  owing  to  careless  methods  in  vogue,  the  movements 
of  the  lower  jaw  for  the  purpose  of  mastication,  with  a  large  percent- 
age of  artificial  dentures,  are  restricted  simply  to  the  up-and-down 
movements  of  the  jaw  or  the  movement  of  occlusion.  By  such  a 
movement  of  the  jaw,  instead  of  mastication  the  patient  is  limited  to 
only  a  crushing  of  the  food,  swallowing  it  without  the  proper  insaliva- 
tion  which  follows  the  free  and  unrestricted  use  of  the  lower  jaw. 

To  construct  an  artificial  denture  which  shall  permit  of  the  free  and 
unrestricted  use  of  the  lower  jaw  several  points  must  be  carefully  con- 
sidered, and  these  cannot  be  better  presented  than  in  the  language  of 
Dr.  Bonwill,  who  is  the  author  of  a  series  of  articles  entitled  "The 
Geometrical  and  Mechanical  Laws  of  the  Articulation  of  the  Human 
Teeth."  In  these  articles  he  calls  attention  to  a  few  conditions  which 
exist  in  every  normally  articulated  natural  denture,  and  with  a  special 
apparatus  of  his  own  invention,  called  "  the  anatomical  articulator,"  he 
applies  his  conclusions  to  the  arrangement  of  artificial  teeth.  His  first 
important  observation  is  with  reference  to  the  shape  of  the  lower  jaw, 
it  being  of  a  peculiar  tripod  arrangement  and  forming  an  equilateral 
triangle.  "  From  the  centre  of  one  condyle  to  the  centre  of  the  other 
four  inches  is  about  the  average  distance,  and  it  will  also  be  found  that 
from  the  centre  of  each  condyloid  process  to  the  median  line  at  a  point 
where  the  inferior  centrals  touch  at  the  cutting  edge  is  also  about  four 
inches."  The  sides  of  these  angles,  he  asserts,  never  vary  more  than 
half  an  inch,  which  would  make  little  difference  in  describing  the  arc 
of  a  circle.  "  No  matter  what  the  width  from  one  condyloid  process  to 
the  opposite  process,  the  distance  is  the  same  from  the  processes  to  the 
median  line  of  the  lower  jaw  at  the  cutting  edges  of  the  central  incisor 
teeth."  .  .  .  .  "  The  jaw  forms  a  perfect  triangle  for  the  purpose  of 
bringing  into  contact  the  largest  amount  of  grinding  surfaces  of  the 
bicuspids  and  molars,  and  at  the  same  time  have  the  incisors  on  one  side 
at  once  come  into  action  during  those  lateral  movements."  .... 

"  It  will  also  be  found  that  from  the  cuspids,  the  bicuspids  and 
molars  run  in  nearly  a  straight  line,  instead  of  a  circular  one,  back 
toward  the  condyloid  process,  enabling  them  to  keep  the  largest 
amount  of  surface  always  presented  for  mastication."  The  next  import- 
ant observation  has  reference  to  the  position  and  relation  of  the  incisor 


OCCLUSION  AND  ARTICULATION. 


371 


teeth  :  "  The  upper  incisors  should  over-jet  the  lower  incisors,  while 
the  lower  have  a  corresponding  under-bite  ;  without  this  arrangement 
the  incisor  teeth  would  lose  their  function.  Were  the  incisors  to  strike 
directly  upon  each  other,  the  power  to  cut  off  food  would  be  very  much 
lessened.  The  normal  arrangement  of  the  incisor  teeth  is  shown  in 
Fig.  428.     Where  there  is  an  over-bite  and  an  under-bite  of  the  incisor 

Fig.  428. 


teeth,  just  in  proportion  to  their  depth  will  be  the  length  of  the  cusps 
of  the  cuspids,  bicuspids,  and  molars." 

The  next  observation  has  reference  to  the  curvature  of  the  teeth  in 
the  jaw,  which  is  formed  by  the  dipping  down  of  the  second  bicuspid 
and  shortening  of  the  posterior  cusp,  with  a  turning  upward  of  the  first 
and  second  molar  teeth  toward  the  condyle  of  the  jaw,  as  illustrated  in 
Fig.  430,  and  is  also  illustrated  in  Fig.  427,  which  is  reproduced  from  a 
life-size  engraving  from  Black's  Dental  Anatomy.  This  vertical  curva- 
ture "  commences  at  the  first  molar  tooth, '  although  it  shows  itself 
slightly  at  the  bicuspids ;  practically,  it  need  only  commence  at  the  first 
molar,  and  this  curvature  is  proportioned  to  the  under-bite  and  over-bite 
of  the  incisor  teeth." 

The  purpose  of  this  curvature  at  the  ramus,  as  shown  in  Figs.  427 
and  430,  is  obvious  :  when  the  lower  jaw  is  protruded  during  the 
incisive  function  (Fig.  429)  the  molar  teeth  are  in  contact  at  the  same 

Fig.  429. 


time  as  the  cutting  edge  of  the  incisor  teeth,  while  the  cuspids  and 
bicuspids  swing  free.  This  prevents  anything  more  than  mere  contact 
of  the  incisor  teeth ;  and,  applying  the  principle  to  the  arrangement  of 
artificial  teeth,  it  establishes  contact  at  the  heel  of  the  plate  at  the  same 
time  the  incisor  teeth  strike,  and  prevents  the  displacement  of  the  den- 


372 


THE  ''BITE"    OR   OCCLUSION. 


ture.     The  length  of  the  cusps  of  the  bicuspid  and  molar  teeth  has  a 
definite  relation  to  the  lateral  movement  of  the  lower  jaw.     The  buccal 

Fig.  430. 


cusps  of  the  lower  bicuspid  and  molar  teeth  are  usually  shorter  than  the 
lingual  cusps,  while  the  reverse  is  true  of  the  upper  bicuspids  and 
molars.  The  purpose  of  this  arrangement  can  be  easily  seen  by  refer- 
ring to  Fig.  431.     When  the  lower  jaw  is  extended  to  the  left  side,  as 


Fig.  431. 


in  the  figure,  and  mastication  is  being  performed  on  the  left  side  of  the 
mouth,  the  cusps,  both  the  lingual  and  the  buccal,  are  found  opposite 
each  other,  while  the  food  is  pressed  into  the  sulcus  between  these  cusps. 
Now,  if  there  is  no  contact  upon  the  opposite  side  of  the  mouth,  the 
plate  would  be  in  great  danger  of  tilting  or  dropping  on  the  side  oppo- 
site the  one  in  use.  But  by  the  proper  shaping  of  the  cusps  of  the 
bicuspids  and  molars  we  find  that  we  can  obtain  upon  the  opposite  side 
of  the  mouth  contact  between  the  lingual  cusps  of  the  upper  molar 
teeth  and  buccal  cusps  of  the  lower  molars,  which  prevents  displacement 
of  the  denture  opposite  the  side  in  action. 

"  By  drawing  two  lines  from  T  to  a  and  T  to  e,  in  Fig.  428,  we 
have  the  lengths  of  the  cusps  of  the  bicuspids,  b  in  the  upper  and 
c  in  the  lower,  and  also  d,  the  second  upper  molar.  The  depth  of 
the  under-bite  is  one-eighth  of  an  inch  from  the  cutting  edge  of  the 
inferior  central  incisor,  c,  to  that  of  the  superior  central  incisor,  a.  Did 
the  teeth  extend  as  far  back  as  T,  there  would  be  flat  surfaces  at 
those  points.  But  in  articulating  artificial  teeth,  when  the  superior 
second  molar  is  reached  its  distal  cusp  has  to  be  raised  from  line  Te  to 
Ta  (Fig.  428)  to  allow  the  molar  teeth  on  the  opposite  side,  not  in  mas- 
tication, to  touch  for  merely  balancing  the  plate,  as  Fig.  431,  31,  N; 
otherwise  the  second  molars  would  be  of  no  use  in  lateral  movement, 
nor  would  the  first  molars.  This  curvature  at  the  ramus  (see  Figs.  42^ 
and  430)  commences  at  the  first  molar,  although  it  shows  itself  slightly 
in  the  bicuspids.  Practically,  it  need  commence  at  the  first  upper 
molar.     This  curve,  then,  will  always  be  proportioned  by  the  under- 


OCCLUSION  AND  ARTICULATION.  373 

bite  at  a,  e.  The  length  of  the  cusps  or  bicuspids  will  never  be  more 
than  an  eighth  of  an  inch  normally  ;  the  groove  deeper  than  that  would 
cut  the  palatal  cusp  off  and  make  of  it  a  cuspid.  It  would  in  reality  be 
cut  in  twain. 

"  So  that  when  a  first  superior  bicuspid  is  seen  it  can  very  well  be  told 
from  the  length  of  the  cusps  whether  the  jaw  from  which  it  came  had 
a  depth  of  under-bite  of  one-sixteenth  of  an  inch  or  more.  Where  the 
teeth  all  strike  fairly  one  upon  the  other,  without  over-bite,  then  there 
is  no  occasion  for  cusps.  If  originally  there,  they  would  soon  be  worn 
ofP  from  the  abnormal  articulation." 

As  the  lower  jaw  is  drawn  into  position,  the  buccal  cusps  of  the 
lower  molars  travelling  into  the  sulcus  and  toward  the  lingual  cusps  of 
the  upper  molars  on  the  side  in  use,  we  find  the  buccal  cusp  of  the 
opposite  lower  molar  travelling  toward  the  buccal  cusp  of  the  upper 
molar  on  the  side  not  in  use,  keeping  a  constant  contact  for  the  pur- 
pose of  supporting  the  denture  upon  that  side  of  the  mouth  during  mas- 
tication on  the  opposite  side.  The  same  principle  holds  good  when 
mastication  is  performed  on  either  side  of  the  mouth. 

Fig.  431  shows  the  position  of  molars  and  bicusj^ids  during  mastica- 
tion on  the  left  side,  with  a  balancing  contact  of  the  molar  teeth  on  the 
opposite  side  of  the  mouth. 

The  next  observation  made  by  Dr.  Bonwill  has  reference  to  the  rela- 
tive position  and  size  of  the  teeth  in  the  arch.  This  is  illustrated  in 
Figs.  432,  433.  An  equilateral  triangle  is  formed  with  a  base  of  four 
inches,  the  distance  from  the  centre  of  one  condyle  of  the  lower  jaw 
to  the  centre  of  the  opposite  condyle,  and  represented  by  the  points 
A,  A  in  the  figures.  From  the  points  A,  A  a,  line  is  taken  to  the  cut- 
ting edge  of  the  central  incisor  teeth  at  the  median  line,  which  repre- 
sents the  apex  of  the  triangle. 

We  now  take  a  pair  of  dividers  and  obt,ain  the  combined  width  of 
the  superior,  central,  lateral,  and  cuspid  teeth  on  one  side.  A  line  is 
now  drawn  from  the  point  (F),  or  the  cutting  edge  of  the  superior 
central  incisors  at  the  median  line,  to  a  point  between  the  condyles,  or 
midway  between  the  points  A,  A  (Fig.  433).  This  line  extends  from 
i^  to  T  in  the  diagram,  and  represents  the  median  line  of  the  mouth 
throughout  its  entire  extent.  The  point  of  the  dividers  is  now  placed 
at  the  cutting  edge  of  the  superior  centrals  at  point  F,  while  the  other 
foot  of  the  divider  is  placed  at  point  I  on  the  median  line,  or  just  the 
distance  of  the  width  of  the  superior  central,  lateral,  and  cuspid  teeth 
on  one  side.  The  point  of  the  divider  resting  at  /  is  held  firmly  in 
position,  while  the  point  of  the  divider  at  F  is  made  free,  and  a  com- 
plete circle  described.  The  anterior  segment  of  this  circle  which  inter- 
sects the  median  line  at  F  gives  the  exact  size  of  the  arch  as  it  falls 
directly  upon  the  cutting  edges  of  the  incisor  and  cuspid  teeth.  It 
marks  the  extreme  limit  and  prominence  of  the  cuspid  tooth.  If  a  line 
be  drawn  at  right  angles  to  the  point  where  this  circle  intersects  the 
median  line  at  Y  (Fig.  432)  (or  twice  the  distance  of  the  combined  width 
of  the  superior  central,  lateral,  and  cuspid)  from  the  apex  of  the  triangle,  it 
will  fall  through  the  centre  of  the  second  molar  tooth.  After  arranging 
the  six  anterior  teeth  according  to  the  measurements  given,  a  straight  line 
is  taken  from  the  condyle  of  one  side  of  the  mouth  to  the  distal  surface  of 


374 


THE  ''BITE"    OB   OCCLUSION. 


the  cuspid  tooth  on  the  opposite  side  of  the  mouth.  Another  line  is 
drawn  from  the  condyle  on  one  side  to  the  cuspid  tooth  on  the  opposite 
side  at  its  distal  surface.     These  lines  intersect  the  median  line  at  B. 

Dr.  Bonwill  asserts  that  a  line  drawn  at  right  angles  to  the  median 
line  at  the  point  B  (Fig.  432)  will  pass  through  the  centre  of  the  first 
molar  tooth.  It  may  be  stated  with  reference  to  this  line  that  its  position 
can  be  slightly  altered  according  as  the  width  of  the  incisor  teeth  is  greater 
or  less,  and  also  the  width  of  the  bicuspid  teeth,  but  the  discrepancy  is 
so  slight  that  it  makes  but  very  little  practical  difference  in  the  arrange- 
ment of  an  artificial  set  of  teeth.  By  reference  to  Fig.  432,  which  is 
taken  from  a  life-size  engraving  in  Black's  Anatomy,  it  will  be  found 
that  the  horizontal  line  passes  through  the  middle  of  the  disto-buccal 
lobe  of  the  first  molar  tooth  instead  of  through  the  centre  of  the  tooth. 

Fig.  432. 


The  arrangement  as  shown  in  Black's  Anatomy  has  been  more  uni- 
versal in  the  measurements  made  than  that  shown  in  Dr.  Bonwill's 
diagram. 

One  point  of  the  divider  is  next  placed  at  A  (Fig,  432),  and  the  oppo- 
site point  at  B,  and  a  curve  described  toward  the  buccal  surface  of  the 
mouth  from  B,  and  it  will  be  found  that  this  gives  a  space  between  the 


OCCLUSION  AND  ARTICULATION 


375 


curve  and  distal  surface  of  the  cuspid  tooth,  which  fixes  the  width  of 
the  first  bicuspid  tooth.  One  point  of  the  divider  is  kept  at  A  and  the 
other  point  retracted  to  Y ;  a  second  outward  curve  is  then  described,  and 
the  space  between  these  curved  lines  gives  the  exact  width  of  the  second 
bicuspid  tooth.  The  next  line  is  taken  from  a  point  at  the  distal  surface 
of  the  cuspid  tooth  to  the  condyle  of  the  jaw,  which  Dr.  Bonwill  claims 
will  pass  through  the  buccal  cusps  of  the  bicuspid  and  molar  teeth — 
teeth  approximating  the  natural  or  normal.  This  line,  however,  has 
been  found  in  normal  dentures  to  deviate  slightly  from  the  diagram 
shown  by  Dr.  Bonwill.  By  reference  to  Fig.  432  it  will  be  found  that 
the  two  bicuspids  and  first  molars  will  fall  with  their  buccal  cusps  upon 
this  line,  while  the  second  molar  is  turned  inward,  toward  the  median 
line  of  the  mouth,  and  is  missed  entirely  by  the  line  from  A  and  B 
(Fig.  432). 

This  seems  to  be  a  more  advisable  arrangement  of  artificial  teeth, 
for  if  the  diagram  of  Dr.  Bonwill  is  followed  exactly,  the  disto-buccal 
cusps  of  the  second  molars  are  thrown  too  far  from  the  ridge,  and  there 
is  great  danger  of  excessive  leverage  at  this  point,  which  would  not  be 
the  case  if  the  second  molar  was  turned  toward  the  median  line,  as 
shown  in  Fig.  432. 

With  the  exception  of  this  tooth  and  the  position  of  the  line  which 
defines  the  centre  of  the  first  molar  no  exception  is  taken  to  Dr. 
Bonwill's  measurement.  While  the  drawings  represented  in  Figs.  429, 
430,  431,  and  433  are  theoretical,  they  are  nevertheless  true  ;  but  in 
order  to  make  this  subject  more  practical  two  engravings  from  life  are 
shown  in  Figs.  427  and  432,  with  the  measurements  as  given  by  Dr. 
Bonwill  (page  372). 

Fig.  433. 


In  following  out  the  measurements  as  given  below  the  reader  can 
make  reference  to  both  Figs.  432  and  433,  and  can  make  comparison 
between  the  ideal  and  natural. 

[Dr.  W.  E.  Walker  of  Pass  Christian,  Miss.,  in  Cosmos,  January, 
1869,  calls  attention  to  an  anatomical  feature  of  the  temporo-maxillary 


376  THE  ''BITE"   OR   OCCLUSION. 

articulation,  together  with  its  consequent  effect  upon  occlusion,  which  has 
been  overlooked  in  previous  observations.  In  the  Bonwill  articulator 
the  instrument  is  so  constructed  that  the  plane  of  the  temporo-maxillary 
articulation  is  parallel  with  that  of  the  occlusion  of  the  teeth.  The 
opening  of  the  jaws  of  the  articulator  to  bring  the  tips  of  the  inferior 
and  superior  incisors  into  contact  corresponds  with  the  depression  of  the 
inferior  maxilla.  In  the  Bonwill  instrument  the  angle  formed  by  the 
joint  portion  with  the  horizontal  line  is  but  about  10°  to  15°.  Dr. 
Walker  shows  that  the  angle  in  the  living  subject,  from  which  the  con- 
dyle of  the  inferior  maxilla  diverges  from  the  horizontal  plane  of  the 
glenoid  cavity,  is,  upon  an  average,  35°.  He  has  studied  carefully  this 
forward  and  downward  path  of  the  head  of  the  bone,  and  has  constructed 
an  instrument  which  follows  accurately  the  movements  of  the  human 
jaw  according  to  its  variations  in  individuals.  Models  of  a  perfect  den- 
ture placed  in  the  Bonwill  articulator  have  not  the  precise  physiological 
movements  observed  in  the  human  jaws.  Dr.  Walker  has  demonstrated 
that  this  discrepancy  is  due  to  insufficiency  of  the  angle  at  which  the 
portion  of  the  instrument  representing  the  head  of  the  bone  diverges 
from  a  horizontal  plane.  The  models  transferred  from  the  Bonwill  to 
the  Walker  instrument  have  movements  which  correspond  closely  with 
those  observed  in  the  human  jaws. — Ed.] 

Angles  of  Force  during  Mastication. 

When  the  teeth  are  firmly  imbedded  in  the  alveolar  process  and  sup- 
ported laterally  by  one  another,  a  slight  change  in  the  angle  or  position 
of  the  teeth  is  of  very  little  importance  practically,  but  the  angles  at 
which  teeth  on  an  artificial  denture  are  placed  contribute  largely  to  the 
successful  or  unsuccessful  use  of  that  denture.  It  is  absolutely  necessary 
to  consider  the  lines  of  force,  or  the  mechanical  forces,  during  mastication, 
in  order  to  prevent  displacement  of  dentures  before  the  cutting  edges  of 
the  teeth  come  into  actual  contact.  Fig.  434  outlines  the  position  of  the 
incisors,  bicuspids,  and  molar  teeth  on  opposite  sides  of  the  mouth  during 
the  incisive  function  and  during  mastication,  and  the  lines  of  force  are 
indicated  by  the  darts. 

In  a  large  number  of  cases  where  there  has  been  excessive  resorption 
of  the  ridges  it  is  a  rule  with  a  great  many  operators  to  project  the  cut- 
ting edges  of  the  incisor  teeth  toward  the  lip,  while  the  cervix  of  the 
tooth  is  inclined  toward  the  alveolar  ridge.  The  same  is  true  of  the 
lower  incisor  teeth,  and  is  indicated  by  No.  12.  If  the  mouth  is  thrown 
open,  and  there  is  an  attempt  to  incise  with  the  teeth  in  this  position,  the 
pressure  from  the  lower  tooth  is  against  the  inner  or  lingual  cutting  edge 
of  the  upper  incisor  tooth,  and  the  angle  of  pressure  is  shown  by  the 
dart  from  B  to  A,  which  would  cause  a  tilting  of  the  plate  at  the  heel 
because,  there  being  food  between  the  incisor  teeth,  there  is  no  contact 
between  the  molars.  An  arrangement  of  this  kind,  as  shown  in  No.  12, 
would  have  a  tendency,  as  can  be  seen  by  the  angle  of  these  teeth,  to 
displace  by  tilting  both  dentures  at  the  heel.  Referring  now  to  No.  13, 
we  find  that  by  inclining  the  cervix  of  the  superior  incisors  labially,  the 
cutting  edge  of  the  inferior  incisors  lingually,  the  line  of  pressure  is 
toward  the  centre  of  the  palate  above  and  against  the  labial  cutting  edge 
of  the  superior  incisors,  thereby  supporting  the  denture  during  the  pro- 


ANGLES  OF  FORCE  DURING  MASTICATION.  377 

cess  of  biting  through  the  food.  While  this  arrangement  may  not  be 
wholly  in  accordance  with  a  natural  denture,  and  is  slightly  exaggerated 
in  the  figure,  the  appearance  is  much  better  in  an  artificial  set  than  the 
same  arrangement  might  be  with  the  natural  teeth.     The  slight  change 

Fig.  434. 


No.  15 


No.  13 


No.  10 


No.  12 


No.  14 


of  these  angles  does  not  materially  aifect  the  appearance  of  an  artificial 
denture.  It  must  be  remembered  that  No.  1 3  represents  the  position  of 
the  incisor  teeth  when  the  lower  jaw  is  protruded  for  the  purpose  of 
incising.  If  we  refer  to  No.  14,  we  observe  an  arrangement  of  the 
bicuspids  and  molars  that  usually  accompanies  No.  12.  By  the  leaning 
in  of  the  cervix  toward  the  alveolar  ridge  it  can  readily  be  seen   that 


378  THE  ''BITE"    OB   OCCLUSION. 

when  there  is  food  between  the  teeth  and  pressure  is  exerted,  bringing 
the  lower  teeth  against  the  upper,  the  pressure  would  be  represented  by 
a  line  from  B  to  A,  and  this  pressure  toward  the  buccal  surface  would 
tend  to  displace  the  denture  upon  the  opposite  side  of  the  mouth. 

It  will  be  observed  by  reference  to  No.  15  that  the  necks  of  the  teeth 
incline  away  from  the  ridge,  while  their  cutting  edges  lean  toward  the 
centre  of  the  mouth.  This  is  the  correct  arrangement  of  artificial  teeth 
in  occlusion. 

The  position  of  the  teeth  in  mastication  is  shown  in  No.  10,  with  the 
lower  jaw  protruded  to  the  right  side. 

If  the  food  be  now  grasped  between  the  teeth  arranged  according  to 
this  figure,  the  line  of  force  would  be  as  indicated  in  No.  10,  the  pressure 
being  upon  the  buccal  surface  toward  the  centre  of  the  palate,  while  in 
the  lower  it  would  be  toward  the  median  line  of  the  floor  of  the  mouthy 
as  indicated  by  the  darts. 

When  the  jaw  is  protruded  laterally  for  the  purpose  of  triturating 
the  food,  it  is  gradually  retracted,  drawn  upward  and  toward  the  position 
of  occlusion.  Until  the  cutting  edges  of  the  teeth  strike,  the  pressure 
would  be  toward  and  against  the  lingual  cusp  of  the  upper  molar  in  the 
sulcate  groove.  It  will  readily  be  seen  that  pressure  against  this  point 
would  tend  to  support  the  denture  on  the  opposite  side  of  the  mouth. 
If  the  angles  of  the  teeth  are  arranged  properly,  there  will  be  no  dis- 
placement of  the  denture  while  biting  through  the  food  until  the  cutting 
edges  of  the  teeth  strike,  unless  upon  the  opposite  side  of  the  mouth  there 
was  no  balancing  contact.  The  real  act  of  mastication  occurs  after  the 
cutting  edges  of  the  bicuspids  and  molars  strike,  and  if  at  this  time  we 
have  contact  upon  the  opposite  side  of  the  mouth,  we  find  that  the  den- 
ture would  be  constantly  supported. 

By  reference  again  to  No.  10  the  lines  of  force  indicated  are  seen 
until  the  cutting  edges  of  the  teeth  strike ;  now,  as  the  lower  jaw  is 
retracted  the  molars  and  bicuspids  begin  to  travel,  the  food  being  pressed 
in  the  sulcate  groove  between  the  cusps  upward  and  toward  the  position 
of  occlusion,  the  buccal  cusps  following  into  the  sulcus  of  the  upper 
tooth,  while  the  lingual  cusps  of  the  lower  molar  travel  over  the  lingual 
cusps  of  the  upper  molar.  During  this  time  we  find  the  buccal  cusps 
of  the  lower  molar  on  the  opposite  side  travelling  into  the  sulcus  of  the 
upper  molar  and  toward  its  buccal  cusps,  keeping  a  balancing  contact  on 
the  side  opposite  the  one  in  action.  A  practical  application  of  the  angles 
of  force  during  mastication  can  probably  be  more  clearly  demonstrated 
by  reference  to  Fig.  435,  No.  16.  Here  is  shown  a  case  of  lower  central 
incisors  and  cuspids,  with  their  abraded  cutting  edges  bevelled  away 
from  the  lingual  surface  toward  the  labial  side  of  the  tooth.  The  second 
molar  tooth  tilts  forward,  owing  to  a  loss  of  the  first  molar  and  bicuspid 
tooth.  No.  17  shows  a  faulty  arrangement  of  the  artificial  molars  in 
which  the  same  conditions  hold  good  as  in  No.  16.  No.  18  illustrates 
an  arrangement  of  the  molars  by  which  much  greater  stability  of  the 
denture  can  be  secured. 

There  are  other  points  to  be  considered  in  the  arrangement  of  teeth 
besides  mastication.  The  strength  and  duration  of  artificial  teeth  on  a 
denture  or  a  "  bridge,"  and  also  the  base-plate  of  the  denture  as  well,  de- 
pend upon  the  manner  in  which  the  occluding  teeth  strike.  If  they  strike 


ANGLES  OF  FORCE  DIJBINQ  MASTICATION.  379 

as  shown  in  Fig.  434,  No.  14,  there  is  a  great  strain  on  the  superior 
denture  throughout  the  centre  of  the  palatine  portions,  which  eventually 
results  in  a  splitting  or  bending  of  the  plate.  The  individual  teeth  are 
also  liable  to  be  fractured  or  forced  from  the  plate,  this  latter  condition 

Fig.  435. 


No.  18 


occurring  more  frequently  in  ridged  appliances,  such  as  bridge-work,  and 
is  an  extremely  difficult  break  to  repair.  The  direction  in  which  force 
is  exerted  during  mastication  and  during  the  incisive  function  should  be 
closely  observed  in  order  to  place  the  teeth  in  a  position  which  will  enable 
them  to  resist  that  force  to  the  highest  degree,  or  in  a  position  which  will 
afford  the  greatest  mutual  support  between  the  base  of  the  denture  and 
the  teeth.  By  giving  strict  attention  to  these  points  many  annoying 
accidents  will  be  avoided. 

With  the  foregoing  basis,  it  remains  to  adopt  some  apparatus  by 
which  may  be  studied  and  obtained  the  various  movements  of  the  lower 
jaw  out  of  the  mouth.  As  has  been  seen  by  the  preceding  observations, 
the  over-bite  of  the  incisor  teeth,  the  position  of  the  teeth  in  the  arch, 
the  vertical  curvature  in  the  bicuspid  and  molar  region,  the  length  of 
the  cusps,  all  have  a  definite  relation  to  each  other  and  cannot  be  followed 
abstractedly.  It  will  not  be  possible  to  carry  out  the  provisions  of  this 
articulation  without  having  the  means  of  actual  measurement.  There  is 
a  vertical  curvature  in  the  molar  region,  but  this  curvature  will  be  of 
no  service  unless  properly  proportioned  to  the  over-bite.  If  the  incisor 
teeth  are  arranged  with  a  very  slight  overlap,  "  or  only  enough  to  prevent 


380 


THE  ''BITE"    OB   OCCLUSION. 


Fig.  436. 


W.  G.  A.  Bonwill's  articulator. 


hissing/'  the  incisive  function  of  the  incisor  teeth  is  sacrificed,  and  the 
appearance  of  the  incisor  teeth  will  be  unnatural.  If  the  incisor  teeth 
are  arranged  regardless  of  the  position  of  the  molars  and  the  natural 
amount  of  overlap  given,  then  lateral  movements  of  the  jaw  will  be 
interfered  with,  and  the  patient  will  be  restricted  simply  to  the  up-and- 
down  movements  of  the  jaw.  Means  must  be  adopted  whereby  these 
various  conditions  can  be  measured  or  relatively  proportioned  out  of  the 
mouth,  and  this  cannot  be  accomplished  without  being  able  to  obtain 
the  movements  of  the  lower  jaw.  An  instrument  for  this  purpose  is  the 
"anatomical  articulator." 

Anatomical  Articulator. — The  anatomical  articulator  is  composed 
of  brass  wire  and  tubing,  and  is  illustrated  in  Fig.  436.  It  consists  of  a 
base  and  two  brass  bows,  the  bows  being  detachable  by  loosening  the  set- 
screws.  The  articulator  as  seen 
in  the  cut  is  in  the  position  for 
use,  the  uppermost  bow  being 
much  narrower  than  the  lower 
bow.  The  cross-bar  or  tube,  to 
which  the  narrow  bow  of  the  ar- 
ticulator is  attached,  corresponds 
to  the  base  of  the  triangle  or  the 
line  from  a  to  a,  Figs.  432  and 
433.  At  either  extremity  of  the 
cross-bar  is  an  eyelet  through 
which  the  "  condyle  "  of  the  ar- 
ticulator works. 

The  two  spiral  springs  back  of  the  condyle  represent  the  muscles, 
and  serve  to  keep  the  casts  in  the  position  of  occlusion,  except  when 
moved  about  to  get  the  diiferent  bearings  of  the  artificial  teeth. 

In  mounting  cases  the  narrow  bow  should  always  receive  the  upper 
model,  whether  that  be  an  articulating  model  or  the  model  upon  which 
a  denture  is  to  be  constructed,  and  the  wide  bow  should  at  all  times 
receive  the  model  of  the  lower  jaw. 

The  first  step  in  the  process  of  mounting  a  case  is  to  loosen  the  two 
set-screws  and  push  the  brass  bows  firmly  back  in  their  respective  sockets, 
and  then  hold  them  by  tightening  the  screws. 

Second.  Trim  the  base  of  the  models  so  that  the  plane  of  the  base  A, 
Fig.  437,  will  correspond  to  the  plane  of  the  occluding  surface  of  the 
wax-bite,  B.  The  plane  of  the  base  of  the  models  A,  A  should  be  per- 
fectly horizontal,  and  the  wax-bite  at  B  should  be  also  horizontal  in  the 
region  of'the  six  anterior  teeth,  as  shown  in  Fig.  437.  Attention  to  these 
points  enables  one  to  mount  the  cases  squarely  in  the  articulator. 

Third.  Place  the  plaster  models  in  position  in  the  wax-bite  plates, 
and  fasten  them  at  two  or  three  points  by  melted  wax,  to  prevent  slipping 
of  the  models  during  the  mounting  process. 

Fourth.  Place  the  articulator  with  the  wide  bow  resting  upon  a  piece 
of  paper  on  the  plaster  bench,  and  the  upper  bow  turned  backward. 

Fifth.  The  lower  model  is  now  adjusted  upon  the  wide  bow,  the  heels 
pointing  toward  the  condyles  H,  H,  Fig.  437,  with  the  bite-wax  and 
upper  cast  also  in  position  when  the  narrow  bow  is  turned  to  rest  on  the 
upper  cast. 


ANGLES  OF  FORCE  DURING  MASTICATION.  381 

Sixth.  Take  a  pair  of  dividers,  opened  to  measure  four  inches,  and 
place  one  foot  in  a  depression  at  the  condyle,  H,  then  bring  the  other 
foot  to  the  point  where  the  perpendicular  (median  line)  intersects  the 

Fig.  437. 


B,  occluding  surface  of  wax-bite ;  F,  high  lip  line ;  6,  low  lip  line. 

occluding  line,  B.  The  distance  is  now  to  be  measured  from  the  op- 
posite side  in  the  same  manner. 

Rule. — Let  the  median  line  of  the  mouth,  F  to  T,  Figs.  431  and  432, 
fall  midway  between  the  condyles  of  the  articulator,  and  at  the  same 
time  let  the  median  line  of  the  bite  at  the  occluding  edge  of  wax  be 
equidistant  (four  inches)  from  each  condyle.  When  in  this  position 
pour  plaster,  quite  thin,  over  the  narrow  bow  and  upper  model,  and  at 
once  lift  the  articular  up  by  the  base,  and  make  a  bed  of  plaster  on  the 
table  into  which  the  wide  bow  and  lower  cast  are  placed.  When  the 
plaster  hardens  the  excess  should  be  trimmed  away. 

In  mounting  a  cast  for  an  upper  denture  alone  there  would  be  only 
an  upper  wax  articulating  plate,  and  instead  of  the  lower  on  the  oc- 
cluding surface  of  the  upper  bite  an  impression  of  the  cutting  edges 
of  the  lower  teeth.  Take  an  impression  now  of  the  lower  teeth  in 
wax  and  make  a  model,  and  when  this  is  separated  from  the  impression 
place  the  cutting  edges  of  the  plaster  teeth  in  the  impression  on  the 
occluding  surface  of  the  upper  bite-plate,  and  then  mount  in  the  same 
manner  as  with  entire  dentures.  The  above  method  is  also  followed  in 
mounting  a  full  lower  denture  where  there  are  upper  teeth,  and  will  also 


382  THE  "BITE"    OB   OCCLUSION. 

serve  in  mounting  casts  for  partial  dentures  where  it  is  necessary  to  use 
an  articulator. 

Fig.  397  show  bites  for  entire  dentures  after  mounting  on  the 
anatomical  articulator. 

After  the  plaster  which  has  been  used  to  fasten  the  models  to  the  ar- 
ticulator has  hardened  (the  plaster  above  and  below  the  horizontal  lines 
A,  A,  Fig.  437,  in  which  the  bows  of  the  articulators  are  fastened),  the 
wax-bite  at  the  occluding  surface  should  be  separated  to  allow  the 
lower   model  to  swing  free :  the  teeth  may  then  be  selected. 

At  this  point  must  be  measured  the  distance  from  D  to  J5  on  the 
upper  cast,  and  from  E  to  B  on  the  lower,  with  the  dividers.  This  dis- 
tance, whatever  it  is — say  one  inch  and  a  half — should  be  marked  on 
the  top  of  the  model  by  two  holes  one  inch  and  a  half  apart. 

The  divider  is  now  adjusted  to  measure  the  distance  from  D  to  F, 
which  is  marked  on  the  top  of  the  upper  model. 

The  distance  from  ^  to  6r  is  now  measured  and  marked  on  the  lower 
model. 

The  longer  distance  will  be  recognized  as  the  length  of  the  upper 
and  lower  teeth,  or  lip  line,  while  the  shorter  distances  will  represent 
the  high  and  low  lip  lines- 

The  depression  at  D  and  E  on  the  median  line  of  the  models  is 
usually  selected  about  the  centre  of  the  base  of  the  models. 

If  the  bites  become  destroyed,  these  markings  may  be  referred  to,  and 
the  bite  may  be  re-established  with  a  certain  degree  of  accuracy. 

Plain  Teeth. 

Fig.  407  shows  a  set  of  twenty-eight  plain  teeth.  The  wax  articu- 
lating plates,  or  bite-wax,  should  represent  the  exact  length  of  the 
lips  (lip  line),  B ;  the  highest  point  of  elevation  of  the  upper  lip,  as 
occurs  in  laughing,  high  lip  line,  F ;  the  point  of  forcible  depression  of 
the  lower  lip,  low  lip  line,  C ;  the  proper  contour  of  the  face  and  the 
median  line.  Fig.  437. 

If  these  points  have  been  faithfully  observed,  the  lower  wax  articu- 
lating plate  at  the  median  line  represents  precisely  the  position  of 
the  inferior  central  incisor  teeth.  All  that  is  necessary  is  to  cut  down 
to  the  base-plate  through  the  median  line  of  the  wax,  and  take  out  a 
section,  upper  and  lower,  on  one  side  only,  to  admit  of  placing  the  cen- 
tral lateral  and  cuspid  on  that  side,  as  shown  in  Fig.  437,  After  these 
teeth  are  approximately  arranged  the  measurement  as  given  under  the 
heading  "  Articulator  "  is  to  be  followed  to  fix  their  exact  position  when 
they  should  be  waxed  fast. 

Unless  some  of  the  occluding  surface  of  the  wax  is  removed,  it  would 
require  the  teeth  to  be  placed  longer  than  the  wax-bite.  When  the 
amount  of  overlap  is  determined,  just  that  much  of  the  occluding  surface 
of  the  upper  wax  bite-plate  should  be  removed,  as  shown  in  Fig.  437, 

B  to  a 

After  arranging  the  central,  lateral,  and  cuspid,  enough  wax  is  re- 
moved to  admit  the  first  lower  bicuspid,  which  is  placed  in  the  wax  a 
little  lower  than  the  lower  cuspid.  At  the  distal  surface  of  the  cuspid 
the  circle  is  broken,  as  only  the  six  anterior  teeth  form  the  segment  of 


PLAIN  TEETH. 


383 


a  circle.  Next  turn  the  bicuspid  so  that  the  groove  between  its  diminu- 
tive lingual  cusp  and  buccal  cusp  points  straight  toward  the  inner  border 
of  the  ramus  of  the  jaw. 

The  next  tooth  is  the  upper  first  bicuspid,  which  is  arranged  to  occlude 
with  its  buccal  cusp,  overlapping  the  lower  bicuspid. 

Next  in  order  is  the  second  inferior  bicuspid,  which  is  set  a  little 
lower  in  the  way  that  the  first  bicuspid  inferior  was,  with  its  sulcate 
groove  pointing  straight  toward  the  inner  border  of  the  ramus.  It  is 
followed  by  the  second  superior  bicuspid. 

It  will  now  be  noticed  that  the  occlusal  surfaces  from  the  cuspid  to 
the  distal  surface  of  the  second  bicuspid  have  been  gradually  lowered. 

From  this  ]wint,  the  distal  surface  of  the  second  inferior  bicuspid,  the 
occluding  surfaces  begin  to  turn  upward.  The  first  lower  molar  is 
arranged  with  its  anterior  cusps  on  a  level  with  the  second  bicuspid, 
but  its  distal  cusps  should  be  raised  slightly  above  that  plane.  (See  A, 
page  123.) 

The  second  molar  inferior  is  inclined  still  higher,  and  when  the  upper 
molars  are  placed  in  occlusion  the  vertical  curvature  is  formed,  and  we 
must  now  determine  whether  it  is  too  great  or  small  for  the  over- 
bite. 

Fig.  438  shows  the  teeth  of  one  side  arranged  in  occlusion,  and  while 
the  upper  model  and  wax-plate  are  held  in  position  the  lower  cast  and 

Fig.  438. 


Showing  the  arrangement  of  plain  teeth  in  occlusion,  and  the  manner  of  waxing  the  buccal 
and  labial  surfaces  of  wax-plates. 

wax  are  brought  forward  until  the  cutting  edges  of  the  incisor  teeth  are 
opposite  each  other  (Fig.  440). 

If  there  is  an  even  contact  between  the  upper  and  lower  last  molars 
and  the  superior  and  inferior  central  incisors,  the  curvature  is  correct 
(Fig.  440). 

After  this  point  has  been  ascertained,  the  springs  of  the  articulator 
are  to  bring  the  models  into  the  position  of  occlusion  again,  when 
the  teeth  should  be  fastened  to  the  base-plate  by  flowing  the  melted  wax 
around  the  pins  on  the  lingual  side  and  over  the  necks  on  the  labial  and 
buccal  sides  with  a  hot  wax-spatula,  illustrated  in  Fig.  439.  The  wax 
should  now  be  chilled  in  cold  water  to  prevent  loosening  of  the  teeth. 


384 


THE  ''BITE"    OR   OCCLUSION. 


Fig.  439.   when   the   opposite   side   should   also  be  arranged  after   the 

manner  just  described. 
i  When  both  sides  are  arranged  the  lower  model  should  be 


,  I' 


Fig.  440. 


Showing  the  artificial  teeth  arranged  for  one  side,  and  the  lower  jaw  protruded  for 
incising :  also  contact  of  molars ;  also  of  incision  while  intervening  teeth  swing 
free. 

protruded,  first  forward,  and  then  to  the  right  and  to  the 
left  to  see  that  the  teeth  are  all  in  proper  relation  to  each 
other. 

The  articulation  of  the  cusps  of  molar  teeth  is  admirably 
shown  in  Fig.  441,  which  is  taken  from  a  life  engraving  from 

Fig.  441. 


Black's  Anatomy.     It  indicates  the  proper  angle  at  which  to 

place  artificial  teeth  and  the  manner  of  deepening  the  cusps  to 

effect  a  better  masticating  surface. 

I      I  If  a  plumb-line  were  dropped  from  the  lingual  border  of 

'  the  lingual  cusp  of  the  second  inferior  molar,   it  would  fall 

L     J        clear  of  the  body  of  the  jaw,  and  not  through  the  centre  of 

^*^  the  edentulous  ridge,  as   many  artificial   teeth  are  arranged. 

Wax-spatula,  ^j-^gj^    ^}jg   teeth   are  placed   too   near   the  cheek   it  is  con- 


PLAIN  TEETH.  385 

stantly  irritated,  and  the  teeth  are,  during  lateral  movement,  thrown 
out  of  line  of  use.  The  position  of  the  molar  teeth  would  be  more 
nearly  correct  if  a  perpendicular  line  falling  through  the  buccal  cusps 
would  also  fall  through  the  centre  of  the  edentulous  ridge.  This 
arrangement  might,  upon  first  observation,  appear  to  impede  the  move- 
ment of  the  tongue.  Such  is  not  the  case,  but,  on  the  contrary,  the 
molar  teeth  are  in  the  best  position  to  receive  the  greatest  assistance 
from  the  tongue  and  cheek  in  keeping  the  food  in  position  for  mas- 
tication. 

The  No.  2  Articulator  and  Gtum  Sections. 

Fig.  442  represents  the  use  of  the  plain  line  articulator,  or  the  same 
as  illustrated  in  Fig.  395.     While  it  is  not  possible  to  move  the  casts 

Fig.  442. 


Showing  the  No.  2  S.  S.  W.  articulator,  and  an  upper  and  lower  set  of  gum  sections. 

about  in  this  instrument  as  with  the  anatomical  articulator  to  get  the 
various  bearings  of  the  teeth,  the  same  general  rules  are  followed  in  the 
formation  of  the  arch  and  tlie  arrangement  of  teeth  for  entire  dentures. 

For  partial  cases  this  instrument  is  quite  as  successful  as  any  other, 
because  the  position  of  the  artificial  teeth  will  be  governed  to  a  great 
extent  by  the  natural  teeth  remaining;  but  for  full  dentures  some  ad- 
ditional suggestions  are  necessary. 

After  the  bite  is  mounted,  the  arrangement  of  the  teeth  should  be 
proceeded  with  after  the  manner  illustrated  in  Figs.  438  and  439,  but 
the  adjustment  of  the  overlap  of  the  anterior  teeth  should  be  slight,  the 
superior  incisors  barely  covering  the  tips  of  the  inferior  incisors.  There 
should  also  be  a  slight  space  between  the  labial  surface  of  the  inferior 
and  the  lingual  surface  of  the  superior  incisors,  so  that  these  teeth  shall 
not  quite  touch  in  the  articulator. 

The  strongest  occlusion  should  be  between  the  superior  and  inferior 
bicuspid  and  first  molar  teeth,  while  the  inferior  second  molar  should  not 
be  in  positive  contact ;  and  if  there  are  inferior  third  molars,  with  the 
occluding  surface  pointing  forward,  these  should  not  be  allowed  to  quite 
touch  the  superior  artificial  teeth. 

The  reason  for  this  is,  that  after  the  dentures  are  placed  in  the  mouth 

25 


386 


THE  ''BITE"    OR   OCCLUSION. 


there  is  a  slight  settling,  and  if  the  incisors  were  alloAved  to  strike  in  the 
articulator,  a  more  positive  contact  would  follow  in  the  mouth,  which 
would  cause  a  tilting  of  the  plates.  Again,  if  the  last  molar  strikes  too 
forcibly,  the  denture  would  be  crowded  forward,  and  not  only  loosened, 
but  the  mucous  membrane  would  be  considerably  irritated  by  the  friction. 
Fig.  442  illustrates  the  use  of  "  gum  section  "  teeth,  the  first  section 
containing  a  central  and  lateral  incisor  and  the  cuspid  tooth  ;  the  next 
section,  the  two  bicuspids ;  and  the  next,  the  two  molars.  It  will  be 
seen  that  the  use  of  section  teeth  requires  a  different  method  of  ar- 
rangement, two  or  more  teeth  being  placed  at  the  same  time.  On  the 
proximal  margin  of  each  block  or  section  there  is  an  excess  of  porcelain 
gum,  which  is  to  be  ground  off  to  the  required  amount  to  permit  of 
articulating  the  cutting  edges. 

This  is  called  the  jointing  process,  and  must  be  performed  very  care- 
fully in  order  to  obtain  a  properly  finished  piece.     If  the  joints  are  not 

properly  made  and  protected,  the  dark  vul- 
canite will  be  forced  through  in  vulcanizing 
and  produce  a  discolored  joint. 

Fig.  443  illustrates  in  No.  1  a  hori- 
zontal section  through' the  gum  enamel  of 
a  porcelain  block  and  the  approximating 
edges  A  A,  the  surface  to  be  joined.  If 
care  is  not  taken,  the  result  after  grinding 
may  be  as  shown  in  No.  2,  the  labial  sur- 
face in  contact  with  a  V-shaped  space  back 
of  it,  and  during  the  contraction  of  the 
vulcanite  in  the  hardening  process  the  two 
blocks  may  be  drawn  so  forcibly  against 
each  other  as  to  fracture  a  piece  of  the  porcelain  enamel. 

No.  3  indicates  the  proper  method  of  forming  the  joint  for  vulcanite 
work.  From  one-half  to  two-thirds  of  the  thickness  of  the  blocks 
toward  the  labial  surface  should  be  joined  squarely  against  each  other, 
while  the  inner  third  should  be  given  a  slight  bevel,  as  seen  in  No.  3. 

Fig.  444. 


1,  1,  horizontal  section  of  the  por- 
celain gum  of  a  block  of  three ; 
^^,  proximal  edges  to  be  joined; 

2  A,   V-shaped  or  imperfect  joint: 

3  A,  proper  method  of  jointing  see- 
lions  for  vulcanite  ;  4  A.  proper 
method  of  jointing  for  plate  or 
solder  work. 


Showing  an  upper  set  of  single-gum  plate  teeth  on  gold  plate,  illustrating  the  manner  of  jointing. 

After  the  case  is  inverted  this  V-space  is  to  be  filled  with  cement 
to  prevent  the  vulcanite  from  being  forced  through  the  joint. 

Single  gum  teeth  for  gold  plate  work  should  be  joined  squarely 
against  each  other  through  the  entire  thickness  of  the  block,  as  shown  in 
No.  4,  while  the  complete  set,  so  ground,  is  shown  in  Fig.  444. 


TEMPORARY  DENTURES. 


387 


Temporary  Dentures. 

A  distinction  is  made  by  many  operators  between  "  permanent "  and 
"  temporary  dentures."     Strictly  speaking,  any  artificial  denture  might 

Fig.  445. 


A  cast  showing  recent  extraction  of  six  anterior  teeth. 
Fig.  446. 


Showing  the  arrangement  of  teeth  necessary  in  a  case  like  Fig.  44-5,  where  the  six  anterior  teeth 

were  recently  extracted. 

be  considered  as  temporary,  and  none  as  permanent.    But  as  these  terras 
have  been  given  a  special  significance,  regardless  of  their  real  meaning. 


388  THE  ''BITE"    OR   OCCLUSION. 

"  Temporary  denture  "  is  a  term  applied  to  a  denture  inserted  imme- 
diately upon  or  soon  after  the  extraction  of  the  natural  teeth,  or  before 
the  process  of  resorption  is  complete. 

Fig.  445  illustrates  a  mouth  from  which  the  bicuspids  and  molars  of 
one  side  had  been  extracted  some  six  or  eight  months  before  the  anterior 
teeth.  Resorption  has  been  completed  in  this  region,  and  the  sockets 
from  which  the  teeth  were  extracted  perfectly  obliterated. 

The  anterior  portion  of  Fig.  445  shows  the  margins  of  the  sockets  from 
which  the  six  anterior  teeth  have  been  recently  extracted,  the  impression 
being  taken  as  soon  as  bleeding  had  ceased.  In  such  a  case  no  artificial 
gum  will  be  required,  as  the  ridge  is  already  sufficiently  prominent.  The 
crowns  of  the  artificial  teeth  should  be  placed  in  the  position  formerly 
occupied  by  the  natural  teeth,  with  the  neck  of  the  tooth  extending 
slightly  into  the  empty  socket.  The  outer  wall  of  the  socket  is  formed 
by  the  labial  alveolar  plate,  and  the  labial  surface  of  the  neck  of  the 
artificial  tooth  should  fit  snugly  against  this  in  order  to  have  the  natural 
gum  form  nicely  around  it. 

Fig.  446  shows  the  arrangement  on  a  plain  line  articulator,  with  the 
artificial  crowns  projecting  from  the  natural  gum,  and  the  appearance  for 
a  time  is  natural  and  agreeable.  Back  of  the  cuspid  teeth,  where  resorp- 
tion is  complete,  we  see  the  bicuspid  and  molar  teeth  arranged  with  an 
artificial  gum,  Avhich  is  brought  forward  to  the  distal  surface  of  the 
cuspid  tooth.  This  figure  (446)  also  illustrates  the  arrangement  of  a 
partial  lower  case  in  connection  with  an  upper  having  two  molars  on 
either  side. 

The  Arrangement  of  Teeth  in  Abnormal  Protrusion  of  the 

Lower  Jaw. 

In  the  preceding  illustrations  and  text  the  attention  of  the  student 
has  been  directed  to  normal  conditions,  and  the  normal  arrangement  of 
artificial  teeth  with  those  conditions,  in  order  that  he  may  familiarize 
himself  with  the  various  methods  and  principles  involved,  and  be  able  to 
modify  them  in  the  treatment  of  abnormal  cases. 

Fig.  446  may  be  considered  a  fairly  normal  relation  of  the  edentulous 
ridges,  and  one  with  which  all  of  the  rules  governing  a  normal  articula- 
tion can  be  followed  out  with  a  certain  degree  of  accuracy. 

Fig.  447  shows  an  extremely  abnormal  relation  of  the  alveolar  ridges, 
and  one  requiring  a  considerable  modification  of  the  usual  methods  in 
order  to  arrange  the  teeth  in  a  manner  at  all  satisfactory.  A  protrusion 
of  the  lower  jaw,  however,  within  certain  limits  may  be  met  with  occa- 
sionally, and  a  normal  arrangement  of  the  teeth  obtained,  providing  that 
other  conditions  are  favorable  to  it.  But,  before  attempting  to  arrange 
the  teeth  in  such  cases,  and  while  the  patient  is  still  at  hand,  the  ope- 
rator must  make  some  careful  observations. 

First,  to  ascertain  whether  the  low^er  teeth  can  be  retracted  sufficiently 
to  obtain  an  over-bite  without  interfering  with  the  movements  of  the 
tongue. 

It  is  seldom  possible  to  adjust  the  lower  teeth  toward  the  tongue  far- 
ther than  the  centre  of  the  edentulous  ridge.  If  such  an  operation  is 
attempted,  the  movements  of  the  tongue  will  not  only  be  impeded  and 


TEETH  IN  ABNORMAL  PROTRUSION  OF  THE  LOWER  JAW.   389 

speech  impaired,  but  the  stability  of  the  denture  will  be  affected  by  the 
tongue  constantly  pushing  against  it. 

Second. — It  must  be  ascertained  whether  the  tissues  of  the  upper  lip 

Fig.  447. 


Showing  extreme  protrusion  of  the  lower  jaw,  and  with  antagonizing  casts  on  the  anatomical 

articulator. 

are  sufficiently  lax  to  permit  of  bringing  the  upper  teeth  the  necessary 
distance  forward  from  the  alveolar  ridge  to  obtain  an  over-bite. 

Fig.  448. 


Showing  the  arrangement  of  teeth  necessary  in  a  bite  when  the  lower  teeth  close  outside  of  the 

upper. 

Third. — Will  the  removal  of  the  superior  incisor  teeth  from  the  alve- 
olar ridge  cause  a  continual  loosening  of  the  denture  by  excessiv^e  lever- 
age on  these  teeth  ? 

Fourth. — Whether  the  attempt  to  obtain  a  perfect  ])rofile  will  effect 
too  radical  a  change  in  the  patient's  appearance. 


390 


THE  ''BITE"    OR    OCCLUSION. 


Fig.  448  illustrates  the  arrangement  of  teeth  necessary  in  case  of"  pro- 
trusion so  extensive  as  in  Fig.  447.  The  upper  incisor  teeth  are  arranged 
to  close  inside  of  the  lower,  with  their  labial  surfaces  gliding  closely  on 
the  lingual  surfaces  of  the  inferior  incisors,  the  incisive  function  being 
performed  in  a  reverse  manner  to  that  of  a  normal  arrangement. 

When  the  superior  cuspid  tooth  is  reached  the  first  attempt  is  made 
to  merge  into  a  normal  arrangement. 

This  tooth  is  placed  with  its  anterior  cutting  edge  covered  by  the  in- 
ferior cuspid,  while  the  distal  cutting  edge  is  turned  labially  and  ground 
so  as  to  strike  directly  on  top  of  the  mesial  cutting  edge  of  tlie  first  in- 
ferior bicuspid.  The  first  bicuspid,  superior,  is  ground  and  brought  out 
slightly  more  than  the  cuspid,  and  from  this  point  distally  the  teeth 
assume  their  normal  position.  In  order  to  obtain  a  graceful  arrange- 
ment in  such  a  case,  as  seen  in  Fig.  448,  it  will  be  necessary  to  do  con- 
siderable grinding  and  lapping  of  the  upper  teeth,  which  is  not  at  all 
unsightly  in  this  character  of  case. 

The  facial  expression  following  such  an  arrangement  of  the  teeth  will 
be  improved.  In  marked  protrusion  of  the  lower  jaw,  where  the  natural 
teeth  close  outside  of  the  upper,  and  M'hen  this  condition  has  existed  up 
to  middle  life  with  natural  teeth,  a  correction  of  the  facial  expression 
with  artificial  teeth  should  not  be  attempted. 


The  Arrangement  of  Teeth  in  Abnormal  Protrusion  of  the 

Upper  Jaw. 

A  case  directly  the  opposite  to  the  one  illustrated  in  Fig.  447  is 
shown  in  Fig.  449.  In  this  case  the  protrusion  of  the  upper  ridge  was 
about  half  an  inch  beyond  the  lower,  and,  while  there  was  an  over-bite 

Fig.  449. 


Showing  pldbter  ciituuUtK in  111  aiast  with  ._  \tu  me  Drotrnsioii  (it  tht  upper  jaw. 

of  the  upper  teeth,  the  position  of  the  ridges  would  not  permit  of  bring- 
ing the  lower  into  contact  with  the  upper  for  the  natural  performance  of 
the  incisive  function.  This  function  was  established  between  the  cutting 
edges  of  the  lower  incisor  teeth  and  the  base-plate  of  the  upper  denture. 
The  six  anterior  teeth  were  permitted  to  barely  strike  the  base  of  the  ujiper 
denture  when  the  opposing  bicuspids  and  molars  were  in  occlusion. 

Another  feature  of  this  case  was  the  arrangement  of  third  artificial 
molars,  which  with  the  one  natural  molar  wive  a  masticating;  surface  of 


DIRECT  ANTAGONISM  OF  OPPOSING    TEETH.  391 

four  molars  on  either  side  above.  The  cut  shows  the  exact  size  of  the 
casts  and  their  relation  to  each  other,  indicating  the  necessities  of  the 
case  better  than  if  the  artificial  teeth  were  shown. 

Direct  Antagonism  of  Opposing  Teeth. 

A  third  form  of  abnormality  is  shown  in  Fig.  450.  While  this  case 
is  termed  abnormal  in  comparison  to  an  ideal  arrangement,  it  is  not  ab- 
normal, strictly  speaking.  The  abrasion  of  the  cutting  edges  of  the 
natural  teeth   from  many  years  of  hard  use  and  other  causes,  together 

Fig.  450. 


Showing  the  arrangement  of  upper  teeth  directly  upon  the  abraded  ends  of  the  lower  natural 

teeth. 

with  a  destruction  of  the  natural  over-bite  caused  l)y  the  obtusing  of  the 
angle  of  the  lower  jaw,  which  occurs  with  advancing  age,  is  a  natural 
consequence,  and  direct  antagonism  of  the  opposing  teeth  is  perfectly 
normal  under  such  conditions. 

Persons  of  an  advanced  age,  who  have  lost  all  of  the  upper  teeth, 
but  who  have  retained  a  number  of  the  Tower  teeth,  as  shown  in 
the  illustration,  are  frequently  seen.  These  teeth  are  so  abraded 
that  no  signs  of  cusps  remain,  and  perfectly  flat  surfaces  are  presented 
upon  which  to  articulate  the  artificial  teeth.  If  an  attempt  is  made  tO 
articulate  teeth  with  cusps  to  these  flat  surfaces,  only  the  points  of  the 
cusps  will  be  in  antagonism,  which  would  deprive  the  patient  of  a  thor- 
oughly useful  appliance.  An  over-bite  would  also  be  unnatural,  for 
whenever  we  find  the  bicuspids  and  molars  abraded  there  is  usually  a 
corresponding  abrasion  of  the  incisor  teeth,  and  if  the  patient  had  re- 
tained the  upper  teeth,  they  would  have  been  affected  in  the  same  manner, 
and  antagonism  would  have  been  directly  upon  the  cutting  edges. 

In  articulating  an  upj^er  denture  to  lower  natural  teeth  with  the 
above  conditions  existing,  one  feature  must  be  prominently  borne  in 
mind  by  the  operator — viz.  to  offer  no  obstacle  to  the  perfect  freedom  of 
the  lower  jaw.  To  this  end  the  artificial  teeth  should  be  articulated 
directly  upon  the  ends  of  the  lower  teeth  :  the  cusps  of  the  upper  teeth 
should  also  be  ground  off  and  the  flat  occlusal  surface  roughened.  Tliis 
arrangement  will  permit  a  free  lateral  movement  of  the  lower  jaw,  and 
mastication  will  be   performed  after    the  manner  of   the  millstones  in 


392 


THE  ''BITE''    OR   OCCLUSION. 


crushing  grain.  While  this  arrangement  may  not  afford  the  best  means 
of  performing  the  incisive  and  masticatory  functions,  it  is  tlie  best  that 
can  be  done  under  the  circumstances. 

When  arranging  teeth  to  strike  directly  upon  tlieir  cutting  edges,  the 
lines  of  force  must  be  carefully  studied,  and  any  point  likely  to  produce 
leverage  upon  the  denture  nmst  be  shaped  so  as  to  offer  its  portion  of 
support.  The  upper  incisor  teeth  should  not  be  allowed  to  strike  the 
labial  cutting  edges  of  an  abraded  lower,  but  should  be  placed  squarely 
in  the  centre  of  that  tooth.  The  cutting  edge  of  the  lower  teeth  can 
with  advantage  be  grooved  slightly,  mesio-distally,  and  the  upper  teeth 
articulated  to  this  groove,  as  shown  in  Fig.  435,  No.  18. 

Fig.  450  will  also  illustrate  Fig.  435  as  regards  the  position  of  the 
incisors  and  molars.  In  the  arrangement  of  the  bicuspid  and  molar 
teeth  in  such  cases  care  must  be  taken  not  to  allow  the  antagonizing 
buccal  edges  of  the  opposing  teeth  to  strike  on  the  same  line.  The  upper 
teeth  should  be  projected  either  buccally  or  lingually,  so  that  one  or  the 
other  of  the  teeth  will  drive  the  cheek  and  tongue  away  from  the  line 
of  occlusion  ;  otherwise  there  would  be  great  danger  of  injury  to  these 
tissues  every  time  the  mouth  is  closed. 


Partial  Dentures. 

In  the  selection  and  adjustment  of  the  teeth  in  partial  cases  the  ope- 
rator is  governed  largely  by  the  degree  of  resoi'ption  of  the  alveolar  pro- 
cesses at  the  edentulous  spaces. 

In  Figs.  451  and  453  we  observe  the  loss  of  the  left  central  and 
lateral  incisor,  and,  while  either  case  requires  an  artificial  central  and 


Fig.  451. 


Fig.  452. 


A  cast  indicating  the  need  of  a  gum  sec- 
tion. 


A  cast  showing  the  ajustment  of  a  gum 
section  containing  a  left  central   and 


lateral  incisor  that  will  harmonize  with  the  natural  teeth  of  the  opposite 
side,  the  two  cases  require  an  entirely  different  method  of  treatment. 

Fig.  451  exhibits  considerable  resorption  of  the  ridge  between  the 
points  A  A,  and  should  plain  teeth  be  used  here  it  would  require  a  con- 
siderable thickness  of  vulcanite  or  celluloid  gum  to  properly  restore  the 
contour  of  the  ridge.  A  vulcanite  or  celluloid  gum  is  contraindicated 
in  such  a  case — first,  on  account  of  its  unnatural  appearance ;  second, 
because  it  is  not  sufficiently  strong  and  is  liable  to  fracture  in  a  short 
time. 


PARTIAL  DENTURES, 


393 


Fig.  453. 


A  cast  indicating  the  need  of  plain  teeth. 


The  proper  method  of  treating  these  cases  is  with  a  sectional  block  of 
gum  teeth,  as  illustrated  in  Fig.  452.  A  block  with  the  porcelain  gum  as 
near  the  natural  color  as  possible  is  se- 
lected, with  teeth  of  the  proper  size, 
color,  and  form.  Before  attempting  to 
adjust  the  block  the  plaster  model 
should  be  scraped  slightly,  as  shown 
at  the  points  A  A,  in  order  to  obtain  a 
close  joint  between  the  artificial  gum 
and  the  natural.  The  block  should  now 
be  carefully  placed  in  the  space,  so  as 
not  to  mar  the  contiguous  plaster  teeth. 
The  points  of  contact  should  be  ground 
oif  slightly  from  the  block  until  the 
surface  of  the  artificial  gum  is  con- 
tinuous with  that  of  the  natural,  and  the  artificial  teeth  on  a  line  with 
those  of  the  plaster  cast.  It  should  now  be  fastened  to  the  model  by 
melted  wax,  and  the  lingual  side  of  the  plate  prepared  for  investing. 

Fig.  453  shows  a  model  similar  to  452,  where  but  little  resorption  has 
occurred.  Plain  teeth  are  here  indicated,  and  should  be  so  adjusted  that 
when  the  piece  is  finished  their  necks  will  be  slightly  imbedded  in  the  gum- 
tissue  of  the  ridge.  To  accomplish  this  the  ridge  on  the  model  should 
be  scraped  at  the  points  where  the  necks  of  the  teeth  impinge,  as  shown 
in  Fig.  453.  The  teeth  should  be  ground  so  tliat  they  may  be  placed  in 
alignment  with  the  natural  teeth  represented  on  the  plaster  cast. 
(See  Fig.  454.)  They  should  then  be  fastened  with  wax,  and  the  lingual 
side  of  the  base-plate  prepared  for  investing. 

Aside  from  the  above  conditions,  which  suggest  the  use  of  gum  or 
plain  teeth,  we  must  consider  the  bite  in  order  to  determine  whether  we 
can  use  teeth  with  headed  pins  or  those  with  headless  pins  (plate  teeth). 
In  the  two  illustrations  there  is  sufficient  space  between  the  cutting  edges 
of  the  lower  teeth  and  the  eden- 
tulous ridge,  consequently  we  can  Fig.  455. 
easily  use  teeth  with  headed  pins  if 
the  case  is  to  be  of  vulcanite  or 
celluloid.  If  it  is  to  be  a  gold  plate 
or  silver,  then  plate  teeth  should  be 

Fig.  454. 


used.  If,  however,  the  lower  teeth  almost  touch  the  edentulous  ridge, 
i:he  use  of  teeth  with  headed  pins  would  be  contraindicated,  because  they 
would  require  too  much  thickness  to  the  plate  and  would  prevent  the 
natural  teeth  from  occluding.  When  the  bite  is  close  and  a  vulcanite  plate 
is  contemplated,  plate  teeth  should  be  selected  and  lined  or  backed  with 
gold,  as  shown  in  Fig.  454.  The  thin  gold  tag  attached  to  the  back- 
ing may  extend  posteriorly  far  enough  to  receive  a  firm  attachment  in  the 


394  THE  "BITE"    OR   OCCLUSION. 

vulcanite  plate  (see  chapter  on  Vulcanite),  while  the  thin  gold  will  per- 
mit the  natural  teeth  to  occlude.  The  anterior  view  would  not  be 
unlike  Fig.  452  or  Fig.  455. 

Fig.  456  illustrates  an  extensive  partial  denture  and  the  use  of  teeth 

Fig.  456. 


Showing  the  use  of  teeth  with  extended  necks,  commonly  known  as  "  celluloid  teeth."  The  two 
centrals  and  right  lateral  incisors  are  natural,  and  have  suffered  recession  of  the  gums;  the 
artificial  teeth  are  selected  to  correspond. 

with  extended  necks,  commonly  known  as  teeth  for  celluloid  work.  It 
will  be  seen  by  the  figure  that  the  two  centrals  and  right  lateral  incisor 
are  natural  teeth  which  have  suffered  recession  of  the  gums,  causing  part 
of  the  root  to  be  exposed.  While  the  lip  of  the  patient  would  roll  high 
enough  in  laughing  to  expose  the  neck  of  the  teeth,  it  did  not  rise  suf- 
ficiently high  to  expose  the  unnatural  gum  of  the  denture. 

Failures  with  Partial  Dentures. — Failures  with  partial  dentures 
are  largely  due  to  carelessness  in  adjusting  the  artificial  teeth,  to  avoid 
which  the  student  is  directed  to  the  following  observations  : 

Whenever  a  block  or  plain  tooth  is  to  be  placed  in  contact  with  the 
mucous  membrane  of  the  ridge,  it  is  necessary  to  scrape  the  points  of 
contact  on  the  plaster  cast  slightly,  in  order  to  obtain  a  clean  joint 
between  the  natural  and  artificial  gum.  In  vulcanite  work  the  scraping 
should  be  a  little  more  extensive  than  in  soldered,  for  during  vulcaniza- 
tion the  rubber  forces  the  block  or  tooth  away  from  the  ridge  a  little, 
which  would  cause  a  dark  line  betw^een  the  tooth  and  natural  gum,  or 
there  would  be  a  space.  Scraping  is  done  to  compensate  for  this  slight 
moving  of  the  block  or  tooth,  also  to  obtain  a  little  pressure  upon  the 
natural  gum  to  ensure  a  clean  joint.  The  degree  to  which  this  is  to  be 
performed  depends  upon  the  compressibility  of  the  gum-tissue  in  the 
mouth,  which  should  be  examined  carefully  before  an  alteration  of  the 
model  is  made. 

Wherever  there  are  natural  teeth  which  occlude  in  the  mouth  requiring 

a  partial  denture,  these  should  never  be 
^^*^^-  '^^'  ■  held  apart  by  the  appliance,  except  for 

}  i'  \flF\  extreme  reasons.  It  not  infrequently 
happens  that  an  appliance  consisting  of 
the  bicuspids  and  first  molar  for  both 
THEs  s  ^  D  M  r„.  sides   is  necessary.     The  bite   is   very 

close,  not  giving  enough  room  for  cusps  upon  the  artificial  teeth  without 
holding  the  natural  teeth  apart.  In  such  a  case  facings  or  veneers  are 
used,  which  have  the  appearance  of  the  bicuspid  and  molar  teeth,  but 


LINGUAL  SURFACES  OF  DENTAL  PLATES.  395 

are  perfectly  flat  on  the  reverse  side.  (See  Fig.  457.)  These  teeth  are 
made  for  either  vulcanite  or  solder  work,  but  are  most  exclusively  used 
for  bridge-work.  By  using  veneers  or  facings  the  outward  appearance 
of  the  denture  can  be  made  satisfactory,  while  cusps,  if  necessary,  can 
be  built  up  with  the  vulcanite  or  gold  to  any  required  height. 

As  a  rule,  the  artificial  tooth  should  be  of  the  same  general  form  and 
shape  as  the  natural  tooth  for  which  it  is  a  substitute,  but  this  rule  can- 
not always  be  followed.  It  is  generally  better  to  place  a  cuspid  tooth 
back  of  a  natural  cuspid,  even  though  there  be  room  for  the  lingual  cusp 
of  a  bicuspid.  The  sudden  thickening  of  the  denture  at  this  point  when 
beginning  with  a  bicuspid  tooth  is  a  serious  impediment  to  the  tongue, 
which  would  not  be  so  noticeable  if  the  appliance  were  started  with  a 
cuspid — though  narrower  than  the  natural  cuspid  or  a  veneer — then  fol- 
lowing this  with  a  well-formed  second  bicuspid. 

A  single  artificial  incisor  or  a  central  and  lateral,  as  shown  in  Figs. 
452  and  455,  should  be  placed  with  their  cutting  edges  a  little  longer 
than  the  adjoining  tooth  on  the  plaster  cast,  to  allow  for  the  settling 
of  the  denture.  If  they  are  placed  the  exact  length  at  first,  after  a 
few  days'  wearing  they  will  appear  shorter  than  the  natural  teeth. 

Artificial  teeth  should  be  selected  to  correspond  exactly  with  adjoin- 
ing natural  teeth  in  color,  shape,  and  size. 

The  Proper  Conformation  of  the  Lingual  Surfaces  of 
Dental  Plates. 

Trouble  is  often  experienced  by  patients  in  securing  a  clear  and  sharp 
s  sound  after  they  have  commenced  the  use  of  artificial  dentures.  A 
peculiar  whistling  sound  is  produced. 

It  is  now  proposed  to  give  a  short  description  of  the  mechanism  by 
which  these  sounds  are  produced,  and  to  draw  attention  to  the  import- 
ance of  giving  due  consideration  to  the  shape  of  the  lingual  side  of  the 
plate  if  it  is  desired  to  secure  clearness  and  ease  of  articulation  of  the 
sound  above  referred  to. 

Inspection  of  models  of  the  upper  jaw  in  which  the  natural  teeth  are 
in  place  will  show  that  while  the  lingual  surface  of  the  bicuspids  and 
molars  practically  forms  a  continuation  of  the  lateral  curve  of  the  palatal 
arch,  the  alveolus  behind  the  incisors  is  thickened.  With  the  rugse  a 
nearly  flat  triangular  space  is  often  produced,  bounded  by  a  line  con- 
necting the  distal  surfaces  of  the  laterals  and  the  edges  of  the  alveolar 
sockets.  Viewed  in  longitudinal  section,  a  reversed  curve  is  presented, 
extending  forward  from  the  hard  palate  and  merging  into  the  hollow 
outline  of  the  lingual  surfaces  of  the  incisors. 

Sections  of  models  from  different  mouths  are  shown  in  Figs.  458  to 
463.  The  curves  will  be  seen  to  present  nearly  the  same  general  shape, 
whether  the  arch  be  deep,  like  Fig.  459,  or  shallow,  like  Fig.  461. 

In  Figs.  462  and  463  an  attempt  has  been  made  to  show  the  relative 
positions  of  the  tongue  and  teeth  in  making  the  -s*  and  sh  sounds.  In 
producing  the  sh  sound  (Fig.  463),  the  upper  and  lower  teeth  are  held 
slightly  apart ;  the  tip  of  the  tongue  rests  against  the  gum  behind  the 
lower  incisors,  its  edges  impinging  upon  the  lingual  surfaces  of  the 
bicuspids  and  molars  at  the  junction  with  the  alveolus.  The  result  is  a 
narrow  passage  over  the  centre  of  the  tongue,  the  narrowest  portion 


396 


THE  ''BITE"    OR    OCCLUSION. 


being  ju!?t  back  of  its  tip,  the  passage  being  thus  gradually  enlarged 
both  behind  and  before  its  narrowest  portion.  The  breath,  being  forced 
through  this  narrow  passage,  follows  its  curve,  and  is  impelled  against 
the  tips  of  the  lower  incisors,  the  result  being  the  .s7/  sound. 


Fig.  458. 


Fig.  459. 


Fig.  460. 


Fig.  461. 


Fig.  462. 


Fig.  463. 


In  giving  the  .s  sound  (Fig.  462)  all  the  parts  remain  in  the  positions 
above  described,  except  the  tip  of  the  tongue,  which  is  curved  upward 
to  the  alveolar  border  on  tiie  lingual  side  of  the  upper  incisors,  making 
the  passage  smallest  at  its  outlet  and  projecting  the  current  of  air  against 
the  upper  incisors.  It  will  be  found  bv  experiment  that  if  the  tongue  is 
drawn  Inickward  a  little  from  the  position  described,  the  hissing  sound 


Fig.  464. 


Fig.  465. 


will  be  changed  to  a  whistle.  It  will  be  noticed  that  the  shape  of  the 
palatine  arch  is  such  that  the  tongue  can  readily  conform  to  it,  and  that 
a  passage  between  the  tongue,  palate,  and  alveolar  border  can  be  readily 
formed  by  which  a  clear  articulation  of  the  sounds  in  question  can  be 
produced. 


REMOVAL   OF  CASES  FROM  THE  ARTICULATOR.  397 

As  a  contrast  to  the  figures  already  shown,  attention  is  directed  to 
Fig.  464,  which  is  a  section  of  a  fairly  well-made  vulcanite  plate.  The 
teeth  are  well  arranged,  the  joints  close  and  well  fitted,  the  finish  good. 
It  will  be  observed  that  the  palatal  curve,  if  continued,  would  meet  and 
coincide  with  the  curve  of  the  lingual  surfaces  of  the  incisors,  there 
being  a  break  at  the  point  of  junction  of  the  teeth  and  rubber ;  and  this 
is  so  abrupt  that  it  would  be  impossible  for  the  tongue  to  follow  its  out- 
line, as  it  does  the  curve  of  the  natural  arch  in  Figs.  463  and  464.  The 
reversed  curve,  shown  in  Figs.  458  to  461,  is  plainly  out  of  the  question. 
The  sketch  illustrates  what  is  by  no  means  an  extreme  case.  With 
thinner  teeth  and  a  longer  bite  the  defect  noted  would  be  still  greater. 

If  the  plate  which  is  shown  in  section  in  Fig.  464  were  tilled  in  to 
present  the  outline  shown  in  a  dotted  line  in  Fig.  465,  the  enunciation 
of  the  wearer  would  be  improved,  and  another  very  substantial  benefit 
be  secured — viz.  an  amount  of  strength  which  will  obviate  any  danger 
of  the  plate  cracking  through  the  centre. 

If  the  imitation  of  nature  be  carried  far  enough  to  reproduce  the 
rugae  upon  the  plate,  it  will  be  found  to  be  a  decided  benefit  both  to 
articulation  and  in  the  management  of  food  in  mastication.  When  the 
lingual  side  of  the  plate  is  smooth  the  tongue  has  but  little  power  to  hold 
a  morsel  of  food  upon  it,  while  with  the  rugae  the  food  is  easily  held  and 
managed.  They  are  easily  formed  by  burnishing  a  piece  of  heavy  tin- 
foil over  a  model  showing  them  prominently,  filling  the  depressions  in 
the  tin-foil  with  wax  or  paraffin,  and  then  fitting  and  attaching  it  to  the 
trial-plate  when  waxed  up  and  ready  for  flashing,  leaving  its  edges 
turned  up  so  that  it  will  be  held  securely  in  the  plaster  when  the  plate 
is  flasked.  The  surface  of  the  vulcanite  will  come  out  clean  and  smooth, 
and  will  require  but  little  polishing.  It  will  be  found  that  a  patient 
who  has  once  become  accustomed  to  the  use  of  a  plate  made  as  above 
suggested  will  be  extremely  loath  to  return  to  the  use  of  one  as  ordinarily 
made. 

Removal  of  Cases  prom  the  Articulator. 

After  the  teeth  are  arranged  and  the  waxing  is  finished,  the  cast  with 
the  wax-plate  and  tooth  in  position  should  „       . 

be  removed  from  the  articulator.  „..^— — '--^ — '.,-^ 

This  is  done  by  trimming  off  the 
plaster  which  held  the  cast  to  the  ar- 
ticulator, exposing  the  brass  bows  or 
frame,  and  then,  by  passing  the  point  of 
a  knife  or  spatula  between  the  base  of 
the  cast  and  articulator,  the  two  pieces 
will  readily  separate.  si^^^i^^  ^  pi^,,^^  cast,^itrtrupo- 

TOO  much    force    must    not    be    exerted  rarybase-plate  and  teeth  in  position. 

.  .  .  ,  •!!    1         1  removed  from  the  articulator  and 

in  this    operation,  or  there  will    be    clanger  ready  for  investing;  also  the  man- 

of   fracturing  the  cast.  ^   The  excess  of       folnt^  of^lum^fertl^^^ 
plaster  must  now  be  trimmed   from  the       vesting. 
base  of  the  cast,  when  the  case  is  ready  for  investing. 


CHAPTER    XL 

SELECTING  AND  FITTING  THE  TEETH  ;   ATTACHMENT  TO 
THE  PLATE;   FINISHING. 

By  H.  H.  Buechard,  M.  D.,  D.  D.  S. 


Selecting  the  Teeth. 

If  there  be  any  of  the  natural  teeth  remaining,  these  are  to  furnish 
the  guide  for  the  choice  of  the  artificial  teeth.  It  is  noted,  first  the  color 
of  the  natural  organs,  and  a  sample  shade  selected  which  matches  them 
in  this  particular.  Observe  the  shapes  of  the  natural  teeth,  whether 
they  be  long  or  short,  broad  or  narrow,  thick  or  slender-bodied — 
whether  the  necks  of  the  teeth  be  narrow  or  broad  as  compared  with  the 
width  of  their  cutting  edges.  A  mould  of  teeth  is  to  be  selected  in 
which  all  the  features  of  the  natural  teeth  are  reproduced  as  nearly  as 
possible.  It  is  noted  also  whether  the  lip  be  long  or  short,  and  the 
extent  to  which  the  articulating  wax  is  exposed  by  the  movements  of 
the  lip. 

If  the  jaws  be  edentulous,  the  temperament  of  the  patient  is  deter- 
mined by  the  shape  of  the  arch  and  vault,  by  the  features,  the  color 
of  the  hair,  of  the  eyes,  complexion,  etc.,  as  described  in  the  section  on 
temperaments.    Teeth  appropriate  to  the  temperament  are  to  be  selected. 

The  question  of  gum  or  plain  teeth  is  determined  first  by  the  amount 
of  absorption  ;  for  as  the  artificial  teeth  are  to  replace  the  lost  teeth,  so 
artificial  gum  is  to  compensate  for  deficiencies  made  by  resorption  of 
gum  contour.  If  there  be  no  loss  of  contour,  an  artificial  gum  is  mani- 
festly unnecessary. 

The  material  of  which  the  gum  restoration  is  to  be  made  is  deter- 
mined by  the  exposure  or  non-exposure  of  the  artificial  gum  by  the 
movement  of  the  lip.  Porcelain  gum  approximates  in  appearance  the 
natural  gum  more  closely  than  artificial  gum  of  any  other  substance,  so 
that  when  there  is  marked  exposure  of  this  portion  of  a  denture  the 
porcelain  is  to  be  preferred. 

There  are  unsatisfactory  limitations  as  to  the  amomit  of  arrangement 
possible  with  teeth  having  porcelain  gums,  so  that  cases  which  require 
an  irregular  arrangement  of  the  teeth  are  usually  supplied  with  plain 
teeth,  to  which  a  rim  or  an  artificial  gum  of  one  of  the  vegetable  bases 
is  applied. 

These  several  peculiarities  and  indications  are  noted  when  the  plate 
is  tried  in  the  mouth  and  the  articulation  taken. 

The  antagonizing  models  are  made,  and  usually  mounted  on  an  artic- 
ulator. The  line  on  the  wax  representing  the  middle  line  of  the  face  is 
extended   upward  and  downward  by  a  scratch  on  the  models.     At  a 

398 


SELECTING    THE  TEETH. 


399 


point  about  half  an  inch  above  the  wax  this  scratch  is  intersected  by 
another  line  ;  one  point  of  a  pair  of  dividers  is  placed  at  the  point  of 
intersection,  its  other  point  at  the  line  on  the  wax  representing  the 
length  of  the  lip,  which  is  also  the  length  of  the  teeth,  and  the  distance 
between  the  divider  points  is  then  marked  on  the  side  of  the  model  for 
future  reference. 

If  a  full  denture,  upper  and  lower,  the  middle  line  and  the  length 
of  the  lower  teeth  are  similarly  recorded. 

The  articulating  wax  having  been  built  to  a  form  restoring  the  lost 
facial  contour,  it  is  to  furnish  the  guide  in  setting  the  artificial  teeth  in 
their  relation  to  fulness. 

If  a  full  denture,  it  has  been  determined  by  the  rules  of  temperament 
what  should  be  the  size,  shape,  and  shade  of  the  artificial  teeth,  and  a 
mould  is  selected  from  the  stock  of  the  manufacturer  which  best  corre- 
sponds with  the  indications. 

The  shapes  of  the  single  gum  teeth  appropriate  to  the  several  tem- 
peraments are  shown  in  Figs.  467  to  470.  This  style  of  artificial  tooth 
does  not  oifer  the  same  facilities  for  artistic  arrangement  that  may  be 
made  with  plain  teeth. 


Fig.  467. 


Fig.  468. 


Lymphatic. 
Fig.  469. 


Nervous  temperament. 


Bilious. 


If  a  single  denture  or  a  partial  case,  the  remaining  natural  teeth  serve 
as  guides  in  selecting  the  substitutes  for  the  lost  organs. 

As  a  rule,  the  best  manufacturers  make  artificial  teeth  which  bear  the 
relative  sizes  that  are  found  in  the  natural  teeth.  Being  copied,  in  the 
main,  after  the  natural  organs,  a  mould  of  teeth  which  has  centrals  of 
the  correct  size  and  shape  will  presumably  have  lateral  incisors  accom- 
panying which  are  in  anatomical  correspondence,  so  that  in  selecting 
artificial  teeth  primary  attention  is  directed  to  the  central  incisors.  It  is 
noted,  first,  whether  the  inferior  incisors  are  imusually  flat  or  rounded, 
whether  thick  or  thin — the  superior  incisors  must  be  in  correspondence  ; 
next  the  width  must  be  correct :  as  a  rule,  a  superior  central  incisor  is  at 
its  cutting  edge  as  wide  as  an  inferior  central  and  half  a  lateral  incisor. 

The  lengths  of  the  crowns  of  inferior  and  superior  incisors  are  about 
equal,  although  inferior  incisors,  through  their  lesser  relative  width  and 
by  a  frequent  recession  of  the  gum  from  the  enamel  line,  appear  to  be 


400 


SELECTING   AND  FITTING    THE  TEETH,   ETC. 


longer.  When  set  in  the  proper  arch  the  axis  of  the  superior  cuspid 
should  be  at  the  line  between  the  inferior  cuspid  and  first  bicuspid. 

A  shade  darker  than  the  natural  teeth  should  be  selected  in  preference 
to  one  lighter.  The  shadow  of  the  lip  causes  artificial  teeth  to  appear  of 
a  lighter  color  when  in  the  mouth  than  when  held  in  direct  light. 

Cuspids  are  usually  more  yellow  than  the  incisors  or  bicuspids  :  it  is 
advisable  to  represent  this  peculiarity  in  the  artificial  teeth. 

In  all  cases  select  well-fired  teeth,  those  in  which  there  is  a  blending 
of  the  point  and  neck  colors. 

The  lighter  gum  colors  are,  as  a  rule,  to  be  preferred ;  however,  the 
general  colors  of  the  natural  gums  and  of  the  lips  are  to  form  the  guide 
in  this  particular.  It  would  be  obviously  an  error  to  place  in  the  mouth 
of  an  anaemic  patient  bright-red  or  purple  gums,  and  equally  wrong  to 
use  the  light  gum  shades  for  a  patient  who  is  plethoric  and  has  full, 
dark-red  lips.  The  gums  of  blondes  are  lighter  in  color  than  those  of 
brunettes. 

After  determining  and  selecting  the  form,  size,  and  color  of  the  crowns 
and  the  color  of  the  gum,  the  configuration  of  the  latter  may  form  an 
element  in  .selection,  and  it  should  always  when  block  teeth  are  employed, 
and  may  when  single  gum  teeth  are  indicated.  The  gum  should  be  thick 
enough,  and  yet  no  thicker  than  required,  to  restore  the  lost  contour,  and 
moulds  are  selected  which  require  the  minimum  of  grinding  to  adapt 
them  to  the  indicated  degree  of  contour.  Molars  and  bicuspids  are  to 
be  selected  which  shall  bring  the  distal  edge  of  the  second  molar  to  about 

Fig.  471. 


the  rise  of  the  tuberosities  (Fig.  471,  A):  rarely  should  that  portion  of 
the  tooth  be  beyond  the  middle  of  this  protuberance.  Occasionally  it  is 
advisable  to  omit  a  tooth  from  either  side  to  bring  teeth  of  the  correct 
width  to  the  point  named. 

In  selecting  teeth  for  partial  cases  it  is  noted  first  whether  there  is 
such  a  loss  of  alveolar  contour  at  the  site  of  the  absent  tooth  as  to  de- 
mand restoration  by  artificial  gum.  Plain  teeth  are  to  be  preferred 
wherever  admissible,  but  lost  contour  should  be  restored,  so  that  any 
marked  loss  in  this  particular  demands  a  gum  tooth. 

Teeth  should  as  nearly  as  possible  match  in  shade  the  teeth  on  either 
side.  If  these  be  pulpless  and  markedly  discolored,  their  shades  differing 
greatly  from  that  of  the  vital  teeth,  they  should  of  course  be  bleached  ; 
but  in  lieu  of  bleaching  the  color  of  the  artificial  tooth  is  to  be  between 
that  of  the  vital  and  that  of  the  discolored  teeth.  Marked  contrasts  of 
color  are  to  be  avoided. 

It  is  most  important  that  the  shape  of  the  artificial  teeth  corresponds 


ARRANGEMENT  AND  FITTING    OF  TEETH.  401 

with  that  of  the  natural  organs.  It  is  manifestly  improper  to  place  be- 
side a  rounded  and  narrow-necked  natural  tooth  an  artificial  tooth  having 
a  flat  grooved  face  and  broad  neck. 

The  cervical  line,  where  the  artificial  tooth  touches  the  natural  gum, 
should  correspond  with  the  cervical  lines  of  the  natural  teeth. 

Where  a  plain  tooth  which  is  of  the  proper  length  anatomically  is  found 
to  be  too  short  to  extend  from  the  correct  cutting-edge  length  to  the 
natural  gum,  and  when  long  enough  to  span  the  space,  sets  at  a  more 
obtuse  angle  than  the  adjoining  teeth,  an  artificial  gum  is  the  indication  : 
it  should  be  of  a  size  which  shall  bring  the  tooth  to  the  proper  angle,  and 
to  have  the  crown  of  the  correct  length ;  that  is,  in  anatomical  correspond- 
ence with  its  fellows. 

Teeth  having  their  platinum  pins  in  a  vertical  line  (straight  pins)  are 
to  be  preferred  to  those  having  the  pins  in  a  horizontal  line  (cross  pins), 
on  account  of  their  greater  strength.  The  break  in  the  tooth  represented 
by  the  pin  is  the  weak  spot,  and,  as 

the    stress    upon   an  artificial   tooth  Fig.  472.  Fig.  473. 

tends  to  fracture  it  horizontally,  it 
is  evident  that  if  both  points  of 
lessened  resistance  be  in  a  horizon- 
tal line  the  danger  of  fracture  is 
increased. 

In  selecting  teeth  note  that  the        pjns  lengthwise.  Pins  crosswise. 

distance  between  the  plate  and  the 

lower  pin  of  the  tooth  is  great  enough  to  permit  adaptation  of  the  tooth 
without  cutting  away  the  pin.  If  this  distance  is  very  short,  the  use  of 
cross-pin  teeth  will  be  necessary. 

Arrangement  and  Fitting  of  Teeth. 

If  the  case  be  one  for  the  replacement  of  a  full  upper  denture  by 
single  gum  teeth,  a  layer  of  wax  is  placed  around  the  alveolar  ridge  and 
the  tips  of  the  antagonizing  teeth  are  imbedded  in  it.  At  its  anterior 
aspect  the  wax  is  cut  away  until  it  merely  serves  to  retain  the  artificial 
teeth  when  their  pins  are  pressed  into  it. 

The  anterior  teeth  are  placed  around  the  incisive  arch,  so  that  the 
amount  and  direction  of  the  necessary  grinding  may  be  noted. 

The  directions  of  the  axes  of  the  teeth,  the  lengths  and  prominence 
of  the  cutting  edges  of  the  teeth,  peculiarities  of  arrangement,  and  the 
spaces  to  be  between  the  teeth  are  now  determined. 

A  corundum  wheel  of  coarse  grit,  one-fourth  inch  thick  by  one  and  a 
fourth  inches  diameter,  having  a  round  edge,  is  used  for  the  rough 
grinding. 

The  central  incisors  are  to  be  first  adapted.  Note  the  points  at  which 
the  under  surface  of  the  gum  touches  the  plate  when  the  cutting  edges 
of  the  teeth  are  placed  at  their  proper  length  and  their  proper  distance 
from  the  tips  of  their  antagonists.  Grind  the  teeth  away  at  these  points, 
and  continue  the  testing  and  grinding  until  there  is  a  fair  adaptation  of 
these  two  teeth. 

The  joint  between  them  is  roughly  made,  outlining  the  future  joint, 
and  leaving  sufficient  surplus  to  provide  for  the  finishing  gi'inding.  At 
this  stage  the  central  incisors  receive  their  general  expression.     Repeat 

26 


402  SELECTING  AND  FITTING   THE  TEETH,   ETC. 

the  procedure  with  the  lateral  incisors,  giving  them  the  relative  position 
to  the  central  incisors  suggested  by  the  positions  of  the  antagonizing  teeth, 
or  modifying  their  position  or  direction  according  to  any  unusual  forma- 
tion of  the  alveolar  ridge  at  these  situations.  Rough  grind  now  the  joints 
between  central  and  lateral  incisors.  The  cuspids  are  next  partially  fitted 
after  the  same  manner. 

The  expression  produced  by  these  six  teeth  will  determine  in  a  great 
measure  that  of  the  entire  denture. 

There  is  not  a  great  latitude  of  choice  for  the  arrangement  of  single 
or  any  gum  teeth  which  are  jointed  to  one  another,  so  that  the  prosthetist 
will  find  exercise  for  all  his  taste  and  ingenuity  in  using  what  there  is  to 
the  best  effect. 

If  the  teeth  are  of  the  proper  width,  the  points  of  the  cuspids  will 
now  be  resting  upon  the  middle  of  the  labial  surfaces  of  the  inferior  first 
bicuspids.  The  amount  of  joint-grinding  necessary  to  bring  the  artificial 
teeth  to  their  correct  anatomical  positions  is  now  noted.  This  amount  is 
to  be  divided  among  the  five  joints.  If  advisable  or  necessary  to  leave 
spaces,  it  is  preferable  to  make  that  between  the  centrals  small  but  dis- 
tinct. For  the  final  grinding  a  smaller  wheel  of  fine  grit  is  substituted. 
To  secure  the  accurate  adaptation  of  the  teeth  to  the  plate  some  device 
is  employed  to  show  the  points  of  contact  between  them  and  to  indicate 
when  the  contact  is  perfect.  Some  prosthetists  employ  for  this  purpose 
small  squares  of  thin  carbon-paper  pressed  against  the  plate ;  the  tooth, 
rubbed  against  this,  is  marked  at  the  points  of  contact.  A  black  or  blue 
crayon,  used  to  give  a  colored  surface  to  the  plate,  answers  well :  the 
writer  commonly  marks  the  plate  with  a  blue  pencil.  The  points  indi- 
cated are  ground  away  until  a  uniform  distribution  of  the  color  shows  the 
adaptation  of  the  tooth  to  the  plate  to  be  perfect. 

The  joint  between  the  centrals  is  now  to  be  finished.  Some  operators 
grind  the  joints  upon  the  side,  and  not  the  edge,  of  the  jointing  wheel. 

A  wheel  of  fine  grit  about  two  and  a  half  inches 
Fig.  474.  Fig.  475.       in  diameter  and  perfectly  true  is  revolved  rap- 

idly, and  the  joint  surface  held  lightly  and 
steadily  against  its  side,  thus  forming  a  plane 
surface.  The  tooth  is  then  set  in  position  on 
the  plate,  and  the  amount  of  necessary  grinding 
noted  in  its  fellow,  which  is,  in  its  turn,  ground 
Faulty  joint.       Perfect  joint,     in  such  a  manner  that  the  joint  surfaces  are  in 

contact  throughout  (Fig.  474). 
Great  care  must  be  exercised  that  there  be  no  V-shaped  space  at  the  back 
of  the  joint  (Fig.  474)  :  with  close  contact  of  the  pink  borders  anteriorly, 
or  almost  inevitably  when  the  teeth  expand  in  heating,  the  gum  will  flake. 
The  writer  believes  that  better  joints  are  made  by  using  the  edge  of 
the  jointing  wheel.  Note  the  points  at  which  grinding  is  necessary,  and, 
holding  the  tooth  in  the  thumbs  and  index  fingers  of  both  hands,  pass 
the  joint  rapidly  across  the  surface  of  the  wheel  backward  and  forward, 
using  a  wheel  of  fine  grit  having  a  narrow,  square  edge.  Adjust  and 
joint  the  other  teeth  after  the  same  method ;  and  now  the  points  of  the 
cuspids  should  rest  between  the  inferior  cuspids  and  first  bicuspids. 

The  centrals,  if  there  be  any  variations  in  their  axes  from  the  verti- 
cal line,  should  point  toward,  not  from,  the  median  line  :   the  laterals,  as 


ARRANGEMENT  AND  FITTING   OF  TEETH. 


403 


a  rule,  are  to  be  a  trifle  shorter  than  the  centrals ;  the  cuspids  about  the 
same  length  as  the  latter.  The  distal  edge  of  the  cuspid  is  turned  in,  so 
that  an  arc  of  a  circle  would  be  made  by  the  cutting  edges  of  the  six 
front  teeth. 

In  adapting  the  posterior  teeth,  although  it  is  impracticable  to  carry 
out  Dr.  Bonwill's  injunctions  as  to  correct  occlusion  with  this  type  of 
work,  the  endeavor  should  be  made  to  attain  two  of  the  objects — to 
arrange  the  teeth  so  that,  no  matter  what  the  positions  of  the  jaws  may 
be,  there  shall  always  be  three  points  of  contact  between  the  upper  and 
lower  dentures ;  and  to  lessen  the  amount  of  over-bite  progressively  to 
the  second  molar :  these  effects  are,  however,  mutually  interdependent. 

The  common  fault  in  arranging  the  posterior  teeth  is  in  making  them 
a  portion  of  a  circular  arch  :  the  figure  should  be,  including  the  anterior 
segment,  a  parabola.  Again,  the  arch  is  commonly  made  too  wide  across 
the  second  molars,  thus  removing  the  perpendicular  of  the  teeth  too  far 
beyond  the  centre  of  resistance,  the  top  of  the  alveolar  ridge,  and  pro- 
ducing a  lessened  stability  of  the  piece  during  mastication. 

The  bicuspids  and  molars  are  ground  in  pairs,  exercising  the  same 
care  in  securing  close  adaptation  of  the  bases  of  the  teeth  to  the  plate 
and  in  making  good  joints  as  with  the  anterior  teeth.  The  joint  between 
the  cuspid  and  first  bicuspid  requires  especial  care.  The  latter  tooth 
should  be  ground  well  in,  so  that  it  is  half  hidden  by  the  cuspid.  Un- 
due prominence  of  the  first  bicuspid  is  a  common  fault  in  the  arrange- 
ment of  artificial  teeth. 

The  bases  of  all  the  teeth  should  rest  solidly  upon  the  plate  (Fig. 
476,  A),  thus  bringing  the  strain  upon  the  bodies  of  the  teeth,  and  not 
upon  the  pins  (Fig.  476,  jB),  as  occurs  when  the  teeth  are  improperly 
adjusted. 

Ftg.  476. 


Cases  which  present  a  short  lip  and  a  full  gum  contour  indicate  the 
use  of  plain  teeth.  The  thickness  of  artificial  gum  necessary  to  prevent 
fracture  of  the  latter  would  cause  undue  prominence  of  the  lip. 

If  the  natural  gum  itself  is  exposed  through  the  movements  of  the 
lip  and  the  latter  is  very  full,  plain  teeth  are  to  be  so  fitted  to  the  natu- 
ral gum  as  to  appear  to  be  growing  from  it  (Fig.  476,  C). 

When  plain  teeth  are  to  be  employed,  the  extent  to  which  the  labial 
edge  of  the  plate  is  exposed  through  the  movements  of  the  lips  is  noted, 


404  SELECTING  AND  FITTING   THE  TEETH,  ETC. 

and  it  is  cut  away  until  it  is  scarcely  visible  at  the  angles  of  the  mouth. 
Behind  this  the  alveolar  portion  of  the  plate  is  permitted  to  remain. 
Usually,  the  anterior  edge  of  the  buccal  wall  of  the  plate  will  then  be 
about  betw^een  the  first  and  second  bicuspids,  or  a  little  in  front  of  this 
point.  The  necessity  for  this  form  of  plate  has  been  determined  when 
the  impression  is  taken,  so  that  the  minimum  of  cutting  away  is  re- 
quired. 

The  artificial  teeth  are  set  in  wax  and  their  proper  angle  to  the 
vertical  determined,  which  is  about  that  made  by  the  lower  teeth  with 
the  vertical  of  their  alveolar  wall.  The  lingual  tips  of  the  upper  teeth 
should  be  about  one- thirty-second  of  an  inch  from  contact  with  the  lower 
teeth.  The  edge  of  the  plate  is  filed  away,  so  as  to  support  two-thirds 
the  bases  of  the  artificial  teeth,  the  outer  third  of  the  latter  to  be  imbed- 
ded in  the  natural  gum  :  the  plate  is  then  bevelled  to  a  feather  edge. 

The  central  incisors  are  first  ground  to  the  natural  gum,  next 
the  laterals,  and,  following,  the  cuspids,  giving  to  the  neck  of 
each  tooth  the  curved  outline  possessed  by  natural  teeth.  When  these 
teeth  have  been  adjusted,  a  fine  point  is  passed  around  the  neck  of 
each,  marking  their  several  positions  on  the  models.  Within  this  line  a 
layer  of  plaster  of  uniform  thickness  is  scraped  away — about  one-thirty- 
second  of  an  inch  if  the  texture  of  the  natural  gum  be  firm,  and  more 
if  it  be  soft — and  the  necks  of  the  teeth  placed  in  these  depressions  :  the 
small  sections  of  plate  visible  between  the  teeth  are  removed  in  the 
finishing  operations.  The  first  bicuspid,  M^hether  a  plain  or  gum  tooth,  is 
ground  so  that  its  anterior  edge  at  the  neck  also  presses  into  the  natural 
gum.  All  of  the  posterior  teeth  must  rest  solidly  and  firmly  upon  the 
plate. 

The  choice  of  gum  or  plain  teeth  to  replace  the  bicuspids  and  molars 
is  determined  by  the  extent  of  contour  lost :  if  the  loss  be  sliglit,  the 
restoration  is  usually  made  with  pink  vulcanite,  as  this  material  is  much 
stronger  than  porcelain  for  such  purpose. 

Grinding  Partial  Cases. 

The  proper  teeth  are  selected  for  the  replacement  of  the  missing 
organs,  their  anatomical  forms  and  sizes  corresponding  with  the  natural 
teeth  adjoining.  From  several  samples  procured  from  the  manufacturer  the 
teeth  best  suited  in  color  are  taken.  This  is  determined  by  placing  them 
in  juxtaposition  with  the  natural  teeth.  As  stated  above,  teeth  appear  in 
many  cases  to  change  shade  when  placed  within  the  shadow  of  the  lips, 
and  so  several  are  selected,  the  best  of  which  is  determined  by  the  cru- 
cial test  of  placing  each  in  the  mouth. 

It  is  preferable,  when  and  where  possible,  to  use  plain  teeth  for  par- 
tial cases,  for  when  artificial  gum  is  adapted  as  it  should  be,  its  thinness 
is  a  decided  element  of  weakness.  It  is  permissible  in  most  cases  to 
make,  when  necessary,  plain  teeth  a  little  longer  than  anatomically  cor- 
rect ;  but  if  the  loss  of  gum  contour  at  the  site  of  an  absent  tooth  be 
pronounced,  a  gum  tooth  is  indicated. 

The  teeth  are  placed  on  the  model,  and  the  amount  and  direction  of 
the  grinding  to  be  done  noted.  The  artificial  tooth  is  in  all  respects  to 
restore  the  break  in  the  arch.     It  is  to  be  ground  in  until  its  cutting 


GRINDING  PARTIAL   CASES. 


405 


edge,  the  antagonizing  teeth  permitting,  is  in  the  common  arch  line.  The 
neck  of  the  tooth  is  to  have  the  shape  of  the  adjoining  natural  teeth  and 
to  be  at  the  same  height.  The  rounded  extension  of  the  plate  at  this 
point  is  cut  away  and  bevelled,  supporting  the  base  of  the  artificial  tooth 
and  yet  hidden  by  it.  If  a  gum  tooth  be  used,  the  plate  tongue  should 
be  larger  when  possible,  affording  support  to  part  of  the  porcelain  gum. 

To  adjust  gum  teeth  the  plaster  should  be  colored  by  means  of  a 
crayon  or  carbon-paper  laid  under  the  artificial  gum  to  indicate  the 
points  requiring  grinding.  At  the  completion  of  the  fitting  the  plaster 
should  be  scraped  beneath  the  artificial  gum,  so  that  the  latter  will  press 
firmly  against  the  natural  gum.  The  artificial  gum,  to  be  properly 
adapted,  should  exactly  restore  the  contour  of  the  general  gum.  It  is 
preferable  to  have  too  little  rather  than  too  great  a  fulness. 

As  a  rule,  it  is  advisable  to  have  the  artificial  teeth  a  trifle  longer  on 
the  model  than  the  adjoining  teeth,  or  longer  than  its  position  should  be 
in  the  mouth.  The  yielding  of  the  soft  tissues  to  the  pressure  of  a 
plate  when  the  latter  is  in  position  in  the  mouth  carries  the  artificial 
teeth  higher  than  tliey  are  on  the  model,  so  that,  particularly  in  soft 
mouths,  teeth  which  are  placed  in  correct  anatomical  position  on  a  model 
are  too  short  when  in  the  mouth. 

This  yielding  of  the  tissues  occasionally  so  alters  the  relation  as  to 
throw  out  of  position  the  artificial  teeth  which  have  been  accurately 
fitted  to  the  model.  It  is  usual  in  such  cases  to  fasten  the  teeth  to  the 
plate  by  means  of  adhesive  wax,  and  accurately  adjust  them  while  the  piece 
is  in  the  mouth:  the  wax  softens  sufficiently  to  permit  altering  the  rela- 
tions of  the  teeth,  which  when  properly  adjusted  are  chilled,  carefully 
removed  from  the  mouth,  and  immediately  placed  in  the  investment  of 
sand  and  plaster.  In  some  instances  it  may  be  impossible  to  maintain 
the  relative  positions  of  teeth  and  plate  while  withdrawing  the  piece  from 
the  mouth.  This  is  not  infrequently  the  case  when  the  natural  teeth  are 
long  and  irregularly  disposed,  and  single  artificial  teeth  must  be  set  in 
odd  positions  with  great  exactness.  It  is  advisable  to  have  the  patient 
draw  the  plate  well  into  position,  and  then  take  a  plaster  impression  in- 
cluding several  teeth  on  either  side  of  the  space  for  the  artificial  teeth,  in 


Fig.  477. 


Fig.  478. 


which  the  plate  is  withdrawn  from  the  mouth.  This  impression  is  var- 
nished and  a  cast  made  of  investing  material.  When  this  has  set  hard  it 
is  separated  from  the  impression,  and  the  artificial  teeth  set  in  their  correct 
arrangement.    Stays  are  fitted  as  described  below,  and  additional  invest- 


406  SELECTING  AND  FITTING   THE  TEETH,   ETC. 

ing  material  placed  over  and  around  the  artificial  teeth,  holding  them  in 
position,  and  the  model  serves  as  the  soldering  investment. 

Cases  in  which  the  investment  is  made  in  two  sections,  as  described, 
require  slow  and  gradual  heating  to  prevent  separation  of  the  sections 
during  the  soldering  operation. 

In  well-assorted  stocks  of  the  manufacturer,  blocks  of  two  or  more 
teeth  may  be  found  which  are  well  adapted  for  special  cases  (Figs.  477, 
478).  When  spaces  for  which  these  blocks  are  designed  may  be  so 
fitted  by  them  as  to  restore  perfectly  the  lost  contour,  they  may  be 
employed.  They  possess  the  advantage  of  dispensing  with  gum  joints, 
but  have  the  disadvantage  of  greater  liability  to  fracture.  They  are  to 
be  ground  to  perfect  adaptation  with  the  plate,  joining  the  natural  gum 
by  a  thin  edge. 

The  heads  of  the  pins  are  cut  oif,  and  a  stay  of  plate  No.  26  fitted  to 
their  backs  beneath  the  shoulders  :  they  are  then  invested.  Great  care 
is  necessary  in  heating  and  soldering  such  blocks  to  avoid  fracturing 
them. 

Pull  Dentures. 

To  properly  adapt,  arrange  to  the  best  advantage,  and  to  correctly 
finish  a  full  denture  of  gum-plate  teeth  is  one  of  the  most  difficult  ope- 
rations in  prosthetic  dentistry. 

The  articulating  wax  in  its  upper  and  lower  sections  should  represent 
accurately  the  length  of  the  upper  and  lower  incisors — the  fulness  and 
contour  of  both  dentures.  The  articulation  is  mounted  and  teeth 
selected  which  will  harmonize  in  size,  shape,  and  color  both  of  teeth  and 
gums  with  the  age,  complexion,  and  physiognomy  of  the  patient. 

In  adapting  and  fitting  the  teeth  to  the  plates  it  is  usual  to  regard 
the  lower  wax  as  the  outline  of  the  lower  denture,  this  wax  remaining 
on  the  plate,  and  the  upper  teeth  are  adapted  to  the  plate,  as  described 
above,  the  labial  and  buccal  tips  of  the  teeth  following  the  external  edge 
line  of  the  summit  of  the  wax.  After  the  upper  teeth  have  been  fitted, 
arranged,  and  jointed  in  harmony  with  the  physiognomy,  they  are 
cemented  to  the  plate  by  means  of  adhesive  wax.  The  lower  teeth  are 
now  fitted  to  the  plate,  articulating  with  the  upper  teeth. 

It  will  be  noted  in  fitting  the  teeth  of  lower  dentures  that,  as  a  rule, 
the  articulating  relations  existing  with  the  natural  teeth  are  reversed. 
If  the  upper  teeth  have  been  adapted  so  as  to  have  a  firm  plate  support 
beneath,  the  lower  bicuspids  and  molars  when  in  position  are  found  to 
occlude  not  within,  but  outside,  the  upper.  The  reason  of  this  is  found 
in  the  different  manner  of  resorption  of  the  alveolar  processes  of  superior 
and  inferior  maxillse. 

The  alveolar  process  of  the  superior  maxilla  diverges  from  the  body 
of  the  bone  so  that  during  resorption  it  contracts  in  the  arch  areas 
(Fig.  479,  A).  The  process  of  the  inferior  maxilla  converges  so  that  the 
greater  the  shrinkage  the  wider  the  arch  becomes  (Fig.  479,  B).  If 
teeth  are  arranged,  therefore,  in  correct  anatomical  relation  in  mouths 
where  there  has  been  extensive  loss  of  process,  the  upper  teeth  are 
inevitably  placed  beyond  the  centre  of  resistance,  the  apex  of  the  ridge, 
or  by  narrowing  the  width  of  the  arch  of  the  lower  teeth  gives  the  lingual 


FULL  DENTURES.  407 

wall  such  an  inward  inclination  that  the  movements  of  the  tongue  are 
restrained  and  tend  to  displace  the  denture. 

Greater  stability  is  given  a  denture  if  the  bases  of  both  lower  and 
upper  teeth  rest  upon  the  summits  of  the  respective  alveolar  ridges. 

Fig.  479. 


While  in  many  or  most  cases  such  an  arrangement  produces  undesirable 
relations  as  to  the  articulation  of  the  dentures,  divergence  from  it  de- 
creases the  stability  of  the  pieces,  so  that  it  is  preferable  to  compromise, 
giving  the  tongue  as  great  a  latitude  of  movement  as  possible  without 
unduly  lessening  the  stability  of  the  denture. 

When  the  arrangement  of  the  teeth  is  completed,  they  are  to  be 
cemented  to  the  plate  for  trial  in  the  mouth.  This  is  best  accomplished 
by  providing  a  wall  which  shall  hold  the  teeth  in  their  respective  posi- 
tions while  being  cemented  to  the  plate.  The  surface  of  the  model 
above  the  plate  line  has  a  series  of  conical  depressions  made,  usually, 
three  on  a  side,  as  shown  in  the  chapter  on  Block  Carving  (Fig.  270) ; 
these  and  the  walls  of  the  model  are  varnished  and  oiled.  A  plaster 
batter  is  applied  over  the  teeth  and  walls  of  the  model,  covering  them 
by  a  layer  about  half  an  inch  thick.  The  plaster  wall  so  made  is 
grooved  at  the  median  line,  so  that  it  will  divide  readily  at  that  point. 
When  the  plaster  has  set  it  is  removed  in  two  sections  and  the  teeth 


408  SELECTING  AND  FITTING   THE  TEETH,   ETC. 

withdrawn  from  their  beds ;  they  and  the  plate  are  boiled  in  the  acid 
solution,  then  dried.  The  pins  of  each  tooth  are  straightened  and 
made  parallel :  this  is  best  done  by  squeezing  them  with  a  pair  of  flat- 
nosed  pliers,  which  will  also  remove  the  film  of  tooth  enamel  which 
occasionally  overlies  the  pins.  The  teeth  are  returned  to  their  beds,  the 
walls  containing  them  adjusted  to  the  model,  and  adhesive  wax  is  melted 
and  applied,  so  that  each  tooth  shall  be  firmly  attached  to  the  plate. 
The  denture  is  now  ready  for  trial  in  the  mouth. 

Trial  of  Denture. 

The  plate  is  placed  in  position  in  the  mouth,  and  it  is  noted,  first, 
whether  the  joint  between  the  central  incisors  is  in  an  imaginary  line 
bisecting  the  face.  When  the  jaws  and  lips  are  closed,  the  edges  of  the 
central  incisors  should  exactly  mark  the  length  of  the  lip,  except  in 
patients  having  an  unusually  short  lip,  when  the  teeth  may  be  longer. 
The  occlusion  is  noted  :  the  teeth  of  both  sides  must  strike  in  biting, 

The  patient  should  feel  no  greater  pressure  upon  one  side  than  upon 
the  other.  The  normal  lip  outline  should  be  restored ;  any  bulging  of 
the  lip  shows  the  gums  to  be  too  full :  it  is  rare  with  gum  teeth  that  the 
gums  are  too  thin.  Teeth  unduly  prominent  or  insufficiently  prominent 
should  be  placed  in  proper  position,  and  any  improvement  possible  made 
by  altering  the  positions  of  the  teeth. 

The  teeth  of  partial  cases  are  to  be  pressed  into  correct  positions,  so 
that  their  necks  appear  to  be  growing  from  the  gum.  If  gum  teeth  be 
used,  their  gums  are  pressed  so  firmly  against  the  natural  gums  as  to 
leave  an  almost  indistinguishable  line  between  the  natural  and  the  arti- 
ficial gum. 

Rimming  the  Plate. 

After  the  teeth  of  a  full  upper  denture  have  been  tried  in  the  mouth 
and  found  to  be  correct,  a  protective  rim  is  to  be  made  extending  over 
the  upper  edges  of  the  gums  for  about  one-eighth  of  an  inch,  and  attached 
to  the  plate  wall  above  the  gums.  It  is  designed  to  prevent  the  entrance 
of  foreign  substances  beneath  the  artificial  gums,  and  to  serve  as  a  pre- 
ventive against  fracture  of  the  tops  of  the  gums.  Usually  these  gum 
sections  are  fractured  by  a  fragment  of  some  foreign  substance  getting 
beneath  the  gum  and  acting  as  a  wedge  between  gum  and  plate. 

A  wall  of  plaster,  as  described  above,  is  made,  enclosing  the  teeth, 
and  when  hard  is  removed.  Each  tooth  is  loosened  in  its  bed  and  re- 
turned to  it.  A  block  of  wax  is  pressed  into  the  lingual  surface  of  the 
plate,  covering  enough  of  the  backs  of  the  teeth  to  hold  them  in  position 
when  the  plaster  wall  is  removed.  Detach  the  wall  and  fill  between  the 
block  of  wax  and  the  teeth  with  plaster,  carrying  the  latter  over  the  occlu- 
sal surfaces  of  the  teeth  (Fig.  480).  When  this  block  of  plaster  has  set  it 
holds  the  teeth  firmly  in  their  relative  positions.  The  artificial  gums  are 
marked  by  a  line  at  a  uniform  distance  from  the  upper  edge  line  of  the 
plate.  The  block  of  plaster  containing  the  teeth  is  removed  from  the 
plate,  and  the  gums  are  ground  down  to  the  line  marked  on  them, 
bevelled,  and  the  cut  surfaces  smoothed  on  a  fine  corundum  wheel.  They 
are  returned  to  the  plate,  still  held  by  the  block  of  plaster.     The  surface 


RIMMING   THE  PLATE.  409 

of  the  model,  the  upper  portion  of  the  plate-wall,  the  plate  heel  over  the 
tuberosity,  and  the  gums  are  oiled  and  covered  by  a  plaster  batter  about 
half  an  inch  thick  and  extending  for  more  than  a  quarter  of  an  inch  over 

Fig.  480. 


Guide  to  hold  single  gum  teeth  together  while  adjusting  a  rim. 

the  porcelain  gums.  This  plaster  forms  an  impression  from  which  a 
model  of  that  portion  of  the  denture  is  to  be  made.  It  is  a  more  satis- 
factory measure  to  make  these  impressions  in  two  sections,  each  of  which 
extends  a  short  distance  beyond  the  median  line  of  the  plate.  From  the 
models  dies  and  counter-dies  are  made,  two  of  each  for  each  side. 

A  strip  of  plate  of  No.  28  gauge  is  swaged  between  each,  and  trimmed 
so  that  it  shall  extend  for  about  an  eighth  of  an  inch  above  the  plate 
edge,  the  lower  edge  of  the  strip  covering  the  tops  of  the  gums  to  a  uni- 
form depth  of  about  one-eighth  of  an  inch.  The  heel  of  the  strip  should 
be  closely  adapted  to  the  tuberosity  and  its  anterior  extremity  a  short 
distance  beyond  the  median  line.  The  strip  for  the  opposite  side  is  to 
be  similarly  made  and  trimmed.  .  The  plate  and  strips  are  boiled  in  acid, 
dried,  the  plate  and  one  strip  adju.sted  to  one  another  with  the  arti- 
ficial teeth  in  position.  The  strip  is  to  be  held  by  the  clamps  of  iron. 
The  block  containing  the  teeth  is  re- 
moved, and  the  plate  set  with  its  alveolar  ^...Jz^^  ^^^' 
portion  resting  uniformly  upon  a  solder- 
ing block.  A  cream  of  borax  is  painted 
along  the  joint  between  strip  and  plate, 
and  two  small  pieces  of  solder  placed  on  the  ledge  formed  by  the  pro- 
jection of  the  strip  above  the  plate  edge.  The  plate  is  now  carefully  and 
uniformly  heated  under  the  blowpipe,  and  by  means  of  a  fine  flame  the 
solder  is  melted,  partially  uniting  the  strip  to  the  plate.  When  the  plate 
is  cool  the  teeth  are  set  in  position  to  see  that  the  position  of  the  band 
strip  is  correct.  A  line  of  borax  is  painted  along  the  lines  of  junction 
between  the  strip  and  plate,  avoiding  the  introduction  of  borax  into  the 
space  to  be  occupied  by  the  tips  of  the  gum  :  plate  and  strip  are  to  be 
held  by  means  of  three  clamps — one  at  the  tuberosity,  one  at  the  anterior 
extremity,  and  one  between  them.  About  four  of  the  small  squares  of 
solder  are  usually  sufficient  to  complete  the  union.     The  plate  is  boiled 


410  SELECTING  AND  FITTING   THE  TEETH,   ETC. 

ill  acid,  and  the  anterior  end  of  the  strip  cut  off  by  means  of  a  saw  exactly 
at  the  median  line. 

The  second  strip  is  applied  to  the  plate,  its  anterior  extremity  cut  to 
make  a  square  joint  with  the  attached  half  of  the  band  or  rim.  It  is 
soldered  as  the  first,  uniting  the  ends  of  the  bands  by  a  very  small  piece 
of  solder.  The  upper  projection  of  the  band  is  cut  down  to  the  plate  out- 
line, rounded  and  smoothed.  The  teeth  are  returned  to  their  positions  in 
the  plate,  and  the  next  operation  proceeded  with — the  fitting  of  the  stays. 

Fig.  482. 


Upper  denture  rimmed. 

Another  but  less  neat  and  accurate  method  of  fitting  a  rim  is  as  fol- 
lows :  Fit  to  the  upper  edge  of  the  plate  and  for  an  eighth  of  an  inch 
over  the  gums  of  the  artificial  teeth  a  strip  of  pattern  tin  :  this  is  to  be 
reproduced  in  plate  of  No.  30  gauge.  Anneal  the  strip  of  metal,  and  fit 
it  to  the  plate  edge  and  over  the  artificial  gums  with  approximate  accu- 
racy. The  plate  is  laid  face  upward  upon  a  block  of  charcoal,  and  a 
couple  of  iron  pins  pressed  into  the  latter,  bracing  it  against  the  heel  of 
the  plate.  The  strip  is  placed  in  its  position  upon  the  plate  and  held 
against  it  by  means  of  two  or  more  iron  pins.  At  the  points  where  it  is 
seen  the  strip  is  in  contact  with  the  plate  borax  is  applied,  and  small 
pieces  of  solder  placed  at  the  points  of  contact.  The  parts  are  then 
tacked  by  melting  the  pieces  of  solder.  Transferred  to  the  model  and 
the  teeth  placed  in  position,  the  contact  of  the  edges  of  band  and  plate 
is  furthered,  and  then  soldered,  the  operations  described  being  repeated 
as  often  as  necessary  to  perfect  the  joint  between  the  plate  and  rim. 
The  edge  of  the  band  covering  the  artificial  gums  is  burnished  down  until 
it  is  within  a  small  fraction  of  an  inch  from  contact  with  them. 

Wiring  Plates. 

When  plain  teeth  have  been  adapted  to  a  plate,  and  it  is  designed  to 
place  over  them  an  artificial  gum  of  one  of  the  vegetable  bases,  it  is 
advisable  to  attach  to  the  upper  edges  of  the  plate  a  continuous  wire, 
to  round  the  upper  edge,  increase  the  means  of  retention  of  the  artificial 
gum,  and  to  lend  additional  beauty  of  finish  to  the  piece.  After  the 
teeth  have  been  fitted  and  tried  in  the  mouth,  the  palatal  line  of  the  base 
of  the  last  molar  is  marked  by  a  scratch  on  the  plate.  Beginning  at  the 
extremity  of  this  tooth,  a  wire  is  to  curve  over  the  ridge  and  follow 
the  upper  edge  of  the  plate  until  it  terminates  at  the  base  of  the  oppo- 
site terminal  molar :  the  stays  of  these  teeth  are  to  abut  with  the  ends 
of  the  wire.  A  piece  of  triangular  wire  of  No.  18  gauge  of  the  proper 
length  is  procured.  This  is  annealed,  boiled  in  the  acid  solution,  and 
one  face  of  it  scraped  to  exhibit  a  fresh  surface.    The  middle  of  the  wire 


WIRING  PLATES. 


411 


is  usually  attached  first.  A  clamp  holds  that  point  of  the  wire  against 
the  plate  at  the  depression  for  the  fraenum,  the  edge  of  the  wire  level 
with  the  upper  edge  of  the  plate,  which  is  then  set  on  a  block  of  char- 
coal, the  alveolar  ridge  portion  resting  upon  the  surface  of  the  latter. 
The  point  of  junction  of  the  wire  and  plate  is  covered  with  borax  and 
a  small  piece  of  solder  placed  over  it.  A  fine  blowpipe  flame  is  directed 
against  the  plate  beneath  the  wire,  carefully  avoiding  contact  of  the  flame 
with  the  loose  ends  of  the  wire,  as  these  latter  fuse  very  readily.  When 
the  solder  flows,  attaching  the  wire  at  this  one  point,  the  clamp  is  re- 
moved and  the  plate  plunged  in  the  sulphuric-acid  solution.  The  plate 
is  placed  upon  the  model  or  die  and  the  wire  bent,  following  the  line  of 
the  plate.  For  about  half  an  inch  on  both  sides  of  the  soldered  point 
the  wire  is  brought  into  close  apposition  with  the  plate,  the  upper  edges 
of  wire  and  plate  in  a  line ;  the  junction  is  boraxed,  a  clamp  placed  at 
the  extremities  of  the  fitted  portions  of  the  wire,  and  joined  to  the  plate 
by  small  pieces  of  solder.  The  remainder  of  the  wire  is,  little  by  little, 
fitted  and  soldered  until  the  extremities  are  attached  and  are  soldered 
fast  to  the  point  at  which  the  disto-palatal  corner  of  the  second  molar 
touches  the  plates.  As  a  final  measure  the  entire  length  of  the  joint 
between  the  plate  and  wire  is  covered  by  borax,  one  or  two  small  pieces 
of  solder  placed  at  points  where  the  solder  may  be  deficient  in  amount, 
and  then  the  blowpipe  flame  is  passed  along  the  joint,  filling  the  latter 
completely  with  the  solder. 

Should  the  case  be  one  retained  by  clasps  and  not  by  the  vacuum 
chamber,  the  wire  is  to  be  attached  before  the  clasps  are  fastened  to  the 
plate.    Before  rimming  or  wiring 

it  should  be  determined  whether  Fig.  483. 

the  plate  edge  is  of  the  proper 
height  or  depth,  for,  should  sub- 
sequent trimming  of  this  portion 
of  the  plate  be  required,  it  is 
possible  a  portion  of  the  wire 
might  need  to  be  filed  away, 
and  thus  mar  the  finish  of  the 
denture. 

Cases  which  have  the  third 
molars  remaining  should  have  the 
wire  carried  around  the  plate  at 
the  bases  of  these  teeth  (Fig.  483). 

The  wall  made  over  the  ex- 
ternal faces  of  the  teeth  is  now 
cut  away  at  the  portions  touch- 
ing the  band  or  wire  until  the 
teeth  are  set  in  the  Avail,  the 
for  the  succeeding  operation. 

If  the  teeth  are  to  be  attached  to  the  plate  by  means  of  vulcanite  the 
wire  is  continued  across  the  palatal  aspect  of  the  palate,  following  a  line 
which  marks  the  base  of  the  wax.  A  pair  of  special,  long  clamps  will  be 
required  to  hold  the  wire  in  contact  with  the  plate  during  the  soldering 
operation. 


wall 


IS 


in   its 
the 


proper  position, 
rim,  and  they  are 


The 
ready 


412  SELECTING  AND  FITTING   THE  TEETH,  ETC. 

Fitting  Stays. 

The  backing  stays  which  are  to  serve  <  as  the  medium  of  union  be- 
tween teeth  and  plate  are  usually  adapted  to  the  teeth  of  partial  dentures 
while  they  are  in  the  first  plaster  wall,  so  that  after  removal  from  the 
mouth  the  piece  may  be  placed  immediately  in  the  soldering  investment. 

Full  upper  or  lower  dentures,  or  both,  when  removed  from  the 
mouth  are  set  on  their  models.  Should  any  alterations  have  been 
made  in  the  positions  of  any  of  the  teeth,  the  gums  must  be  jointed 
again,  so  as  to  restore  the  continuity  of  the  gum  contour.  Any  slight 
grinding  necessary  to  perfect  the  adaptation  of  the  teeth  to  the  plate 
must  also  be  done. 

There  are  two  methods  of  fitting  the  stays  to  the  teeth — the  first 
by  making  a  second  plaster  wall  and  fitting  the  stays  while  the  teeth 
are  held  in  this  manner  ;  the  second  by  investing  the  piece  and  fitting  the 
stays  in  the  soldering  investment.  The  writer  for  several  years  followed 
the  latter  method,  but  has  abandoned  it  for  the  former,  which,  although 
requiring  a  greater  length  of  time,  is  more  accurate. 

After  the  teeth  have  been  enclosed  in  the  second  plaster  wall  the 
adhesive  wax  is  picked  away,  not  removed  by  boiling  water,  as  the 
latter  fills  the  spaces  between  and  covers  the  surface  of  the  teeth  with 
a  film  of  the  cement. 

A  pattern  in  three  sections  of  the  stiff  foil  is  made  for  the  stays — 
one  embracing  the  molars  and  bicuspids  of  one  side,  the  second  those 
of  the  other  side,  the  third  of  the  six  anterior  teeth.  The  line  of  junc- 
tion with  the  plate  should  be  accurate.  These  patterns  are  duplicated 
in  platinous  gold,  the  thickness  of  the  latter  depending  upon  the  amount 
of  stress  to  which  the  teeth  will  be  subjected  :  the  usual  thickness  is  No. 
25  gauge.  For  teeth  requiring  additional  support  No.  24  to  No.  22 
should  be  employed.  The  outline  of  the  pattern  at  the  line  of  the  junc- 
tion with  the  plate  should  be  cut  accurately  in  the  gold. 

Fig.  484. 


Occasionally  it  will  be  found  that  the  backs  of  artificial  teeth  have 
a  very  irregular  surface,  one  to  which  it  would  be  impossible  to  adapt 
the  platinous  gold  as  it  should  be — the  surfaces  of  gold  and  tooth  in 
contact  throughout.  This  difficulty  is  overcome  by  making  the  stays  in 
two  layers,  that  next  to  the  tooth  of  thin  and  pliable  metal,  24-carat  gold 
or  platinum  of  No.  32  gauge.  The  gold  when  used  gives  a  yellow  tinge 
to  the  cutting  edges  of  the  teeth,  the  platinum  a  blue  tinge ;  22-carat 


FITTING  STAYS. 


413 


Fig.  485. 
B 


plate  of  No.  34  gauge  aiFects  the  color  but  little.     The  gold  for  stays  is 
first  annealed. 

The  following  tools  are  spread  before  the  operator,  so  that  each  may 
be  picked  up  when  required  : 

A  pair  of  broad-pointed  steel  tweezers  (Fig.  492) ;  the  pair  accom- 
panying dissecting  cases  is  the  correct  form ; 

A  pair  of  parallel  pliers  (Fig.  484) ; 

Two  plate-files,  one  5  in.  long,  coarse  cut,  the  other  3  in.  long,  fine  cut ; 

A  pair  of  plate-punches,  a  pair  being  selected  which  has  the  shortest 
distance  from  the  joint  to  the  pin,  thus  securing  the  greatest  force  needed 
for  perforating  platinous  gold  :  many  punches  have  the  short  arm  of  the 
punch  so  long  as  to  require  a  strong  force  to  perforate  the  metal ; 

A  countersink  engine-bit  of  about  one-eighth  edge  mounted  in  the 
tool    handle,    for    countersinking    the 
holes  (Fig.  485,  C) ; 

A  chisel  having  a  wedge-shaped  edge 
and  mounted  in  a  handle,  to  split  the 
pins  of  the  teeth  (Fig.  485,  A,  B) ; 

A  small  pot  of  rouge  made  into  a 
paste  with  olive  oil. 

In  fitting  stays  to  single  teeth,  those 
having  irregular  backs,  the  head  of  each 
platinum  pin  is  touched  with  the  rouge 
and  oil ;  a  piece  of  the  thin  metal  is 
cut  the  full  width  and  length  of  the 
crown  and  fitted  so  that  it  makes  an 
accurate  joint  with  the  plate.  It  is 
then,  while  the  base  is  held  in  contact 
with  the  plate,  pressed  against  the  lower 
pin.  The  position  of  the  latter  is  marked 
by  the  rouge.  The  pin-punch  is  placed 
to  cover  the  mark  so  made,  and  the  gold 
is  perforated.  It  is  again  placed  in 
position  behind  the  tooth,  and  the  second  pin  marked  and  the  perforation 
made.  By  means  of  a  rubber  point,  the  erasing  rubber  of  a  lead  pencil, 
the  gold  is  pressed  into  close  apposition  with  the  surface  of  the  tooth. 
The  holes  are  now  countersunk  to  half  their  depth  from  the  palatal  side. 
Over  the  stay  so  adapted  a  second  stay  of  platinous  gold,  No.  27  gauge, 
is  fitted  in  the  same  manner.  The  tooth  is  now  removed  from  its  plaster 
bed  and  a  sharp  point  passed  around  it,  marking  its  exact  width  and 
length  on  the  stay,  which  is  then  trimmed  to  this  line  and  given  rounded 
edges.  At  the  cutting  edge  of  the  tooth  the  platinous  gold  stay  is  made 
one-sixteenth  of  an  inch  shorter  than  the  other,  and  given  a  long  bevel. 
The  pins  are  then  cut  oif  to  within  one-sixteenth  of  an  inch  of  the  stays, 
and  the  projecting  portion  divided  into  halves  by  means  of  the  pin-splitter. 
Care  is  necessary  in  this  operation  that  the  pins  be  not  shaved  away, 
instead  of  being  divided.  The  two  pin  sections  are  bent  back  against 
the  stay,  and  serve  to  hold  it  firmly  against  the  back  of  the  tooth.  The 
edges  of  the  stay  are  given  a  rounded  form,  except  at  the  base,  set  in 
the  walls,  cemented  to  the  plate,  and  the  fixture  then  invested. 

In  fitting  the  stays  to  a  full  denture  it  has  always  been  the  Avriter's 


414 


SELECTING  AND  FITTING   THE  TEETH,  ETC. 


Fig.  486. 


Fig.  487. 


iM 


practice  to  begin  with  the  terminal  molar  of  one  side,  fitting  each  stay 
in  sequence,  so  that  the  second  molar  of  the  opposite  side  is  the  last  stay 
to  be  adjusted.  Cut  from  the  strip  of  metal  a  piece  having  the  width  of 
the  base  of  the  tooth.  The  distal  end  of  the  stay  for  the  second  molar 
is  made  long  enough  to  extend  around  the  gum  to  the  edge  of  the  rim, 
to  which  it  is  ultimately  to  be  attached.  If  the  patterns  for  the  stay 
pieces  are  accurate,  the  section  of  gold  cut  by  them  will  fit  the  plate  at  the 
bases  of  the  teeth ;  if  not,  the  gold  is  to  be  filed  so  that  it  does  fit  closely. 
The  pins  of  the  teeth  are  touched  on  their  ends  with  the  rouge  and  oil, 
and  the  perforations  are  made  as  described.  Each  stay  as  it  is  made  is 
cut  to  the  size  and  form  of  the  back  surface  of  the  tooth  upon  which  it 
is  to  be  placed.  The  form  of  the  stay  for  the  terminal  molar  is  as 
represented  in  the  cut  (Fig.  486). 

The  joint  between  adjoining  stays  is  to  be  cut  square ;  its  base  is  also 
to  have  a  square  edge.     The  other  outlines  are  to  be  bevelled  and  to 
follow  the  form  of  tlie  back  of  the  tooth,  cover- 
ing it  entirely  (Fig.  487).     The    pin-holes  are 
next  countersunk. 

The  stay  for  the  first  molar  is  cut  and  fitted 
in  the  same  manner,  making  a  close  joint  with 
the  gum  portion  of  the  stay  of  the  second  molar. 
The  stays  for  the  bicuspids  are  similarly  fitted,  and  so  on  to  the  terminal 
molar  of  the  opposite  side,  the  stays  being  given  the  forms  of  the  backs 
of  the  individual  teeth,  and  extending  as  far  toward  the  cutting  edges  as 
the  occlusion  will  permit,  the  basal  portion  of  each  stay  fitting  to  the 
plate  closely,  and  its  lateral  walls  in  close  contact  with  the  stays  of  the 
adjoining  teeth.  If  there  be  spaces  between  the  stays  and  the  teeth,  the 
solder  which  joins  the  two  frequently  draws  the  tooth  from  its  position 
when  it  contracts  in  cooling.  The  more  accurate  the  adaptation  the  less 
solder  is  required  to  unite  the  parts,  hence  less  likelihood  of  disturbing 
the  positions  of  the  teeth.  The  contraction  of  a  mass  of  solder  may  also 
cause  an  alteration  of  the  form  of  the  plate  upon  which  it  is  melted. 

When  all  of  the  stays  have  been  fitted  the  plaster  wall  holding  the 
teeth  is  removed.     The  teeth,  stays,  and  plate  are  boiled  in  the  acid 

solution.  The  teeth  are  placed  in  line  before 
the  operator,  and  each  stay  set  beside  the 
tooth  to  which  it  belongs.  Each  is  placed 
on  its  tooth,  and  by  means  of  pliers  bent 
until  it  fits  accurately  the  surface  of  the 
tooth.  The  pins  are  next  cut  off  to  within 
one-sixteenth  of  an  inch  of  the  surface  of 
the  stay,  and  split.  The  split  sections  are 
bent  back,  retaining  the  stay.  Each  tooth 
as  it  has  its  stay  adjusted  and  fastened  is 
returned  to  position  in  the  plaster  wall,  but 
not  before  a  fine  file  is  passed  over  the 
bevelled  edges,  smoothing  the  outlines  of 
the  stay  to  those  of  the  tooth.  When  all  the  teeth  and  stays  have  been 
so  treated,  the  walls  containing  them  are  placed  on  the  model,  and  by 
means  of  adhesive  wax  the  teeth  are  firmly  cemented  to  the  plate. 

If  the  operator  chooses  to  assure  himself  of  greater  accuracy  or  more 


Fig.  488. 


INVESTING   THE  CASE.  415 

thorough  attachment  of  the  stays  to  the  teeth,  and  a  better  finish  to 
their  edges,  the  teeth  and  stays  are  imbedded  in  investing  material, 
thus :  Make  two  beds  of  the  material,  about  one-half  of  an  inch 
thick,  in  each  ;  seven  of  the  teeth  are  placed  in  two  rows,  exposing 
the  surfaces  of  the  stays,  the  teeth  themselves  entirely  enclosed  in  the 
investment  (Fig.  488).  When  this  has  set  each  pin  is  covered  by  borax, 
and  above  each  a  small  square  of  20-carat  solder  is  placed.  The  invest- 
ments are  now  heated  in  a  furnace ;  next  in  a  charcoal  bed  under  the 
blowpipe,  and  when  the  teeth  and  stays  are  made  a  bright  red  by  the 
heat  transmitted  through  the  base  of  the  investment,  the  fine  flame  is 
turned  upon  each  pin  until  the  solder  flows  about  it,  filling  the  counter- 
sink. When  cool  the  teeth  are  boiled  in  acid,  and  each  stay  smoothed 
and  finished  on  the  polishing  lathe.  This  method  ensures  accuracy, 
but  the  experienced  operator  prefers  to  have  the  soldering  of  stays  to 
the  teeth  and  to  the  plate  in  one  operation. 

When  the  cement  which  attaches  the  teeth  to  one  another  and  to  the 
plates  has  hardened,  the  plaster  wall  is  removed.  It  is  noted  whether 
each  tooth  is  in  its  proper  position ;  the  jaws  of  the  articulator  are  brought 
together,  so  that  it  may  be  seen  whether  the  occlusion  is  correct.  The 
teeth  and  plate  are  now  ready  for  investment. 

Investing  the  Case. 

An  investment  is  a  device  designed  to  hold  the  teeth  and  plate  in 
their  relative  positions  during  the  soldering  operation.  It  is  made  of 
a  material  having  a  low  degree  of  conductivity  and  sufficient  coherence 
to  ensure  that  it  shall  maintain  its  form  when  raised  to  a  very  high  heat. 
By  its  relatively  low  conductivity  it  prevents  too  rapid  heating  of  the 
porcelain  teeth  which  it  encloses,  and  also  the  too  rapid  cooling  when  the 
source  of  heat  is  removed ;  either  of  which  is  a  prominent  factor  in  causing 
fractures  of  porcelain.  The  same  physical  property  lends  to  the  invest- 
ing material  the  feature  of  maintaining  the  teeth  at  a  constant  tempera- 
ture during  the  soldering  operation.  Plaster  is  the  basis  of  the  invest- 
ment ;  to  it  are  added  beach  sand  and  asbestos,  so  that  it  will  resist 
fracture  in  heating. 

About  a  gill  of  water  is  placed  in  a  plaster-bowl,  and  to  it  are  added 
two  tablespoonfuls  of  short-fibre  asbestos.  Beach  sand  is  added  until 
the  materials  are  just  covered  by  a  film  of  water,  and  the  mixture  is 
well  stirred  to  distribute  the  asbestos  evenly.  Plaster  of  Paris  is  next 
sifted  in  and  stirred  until  a  soft,  plastic  mass  is  made.  A  spoonful  of 
this  is  placed  upon  a  glass  slab,  making  a  layer  about  half  an  inch  thick. 
The  denture  is  wet  so  that  the  investing  material  will  flow  freely  into 
the  spaces  between  the  teeth.  A  small  portion  of  the  plaster  is  taken 
upon  the  point  of  a  spatula  and  worked  into  the  deepest  portions  of  the 
palatal  surface  of  the  plate  :  little  by  little,  more  investment  is  added 
until  the  plate  is  full,  when  the  material  is  then  packed  between  the 
teeth,  filling  the  spaces  perfectly.  It  is  then  inverted  upon  the  bed 
of  the  material  upon  the  slab,  and  the  investment  built  about  the 
teeth  until  they  are  covered  by  a  layer  half  an  inch  thick.  The 
lingual  surface  of  the  plate  is  covered  to  within  about  half  an  inch  of 
the  bases  of  the  stays.  To  ensure  against  fracture  of  the  investment, 
it  is  the  usual  practice  to  imbed  in  the  investment  a  piece  of  round  iron 


416  SELECTING  AND  FITTING  THE  TEETH,  ETC. 

wire.    This  is  bent  so  that  its  arch  shall  be  about  one-quarter  of  an  inch 
larger  than  that  of  the  teeth.     It  is  set  in  position  when  the  investment 

Fig.  489. 


Upper  denture  invested  and  ready  for  making  the  backings,  and  showing  position  of  wire  to 

guard  against  fracture. 

Fio.  490. 


Lower  denture  invested  and  ready  for  making  the  backings :  A,  position  of  wire  to  guard  against 

■fra  r>t.n  rp 


fracture 


is  half  completed.     When  the  investment  is  perfectly  hard  the  cement 
is  picked  away  piecemeal,  every  particle  being  removed.     Do  not  use 


m  VESTING   THE  CASE.  417 

hot  water  for  melting  out  the  wax  :  it  is  uncleanly,  frequently  leaving 
a  tenacious  film  upon  the  teeth  and  plate,  besides  softening  the  investment. 

In  some  laboratories  the  teeth  and  plate  after  trial  in  the  mouth  are 
immediately  invested,  and  the  stay-fitting  done  while  in  this  encasement, 
using  no  preliminary  wall.  The  writer  followed  this  method  for  some 
years,  but  abandoned  it  for  the  former  method  described,  that  being 
safer  and  more  accurate.  The  patterns  are  made,  and  each  stay  cut, 
fitted,  and  trimmed  as  with  the  method  first  described.  By  means  of 
pliers  they  are  bent  to  fit  the  backs  of  the  teeth  as  closely  as  possible, 
using  especial  care  that  the  edges  of  the  stay  are  in  contact  with  the  tooth. 
The  stays  are  boiled  in  the  acid  solution,  and  their  line  of  junction  with 
the  plate  scraped  clean.  Each  pin  is  now  cut  oif  to  within  one-sixteenth 
of  an  inch  of  the  surface  of  the  stay  and  split  twice  by  means  of  the  pin- 
splitter,  the  cuts  at  right  angles  to  one  another  :  the  four  sections  are  then 
bent  down,  holding  upon  the  stay  firmly.  Care  is  necessary  in  this  opera- 
tion that  not  enough  force  be  applied  to  fracture  the  investment.  Some 
operators  grasp  the  unshortened  ends  of  the  platinum  pins  in  the  jaws 
of  a  pair  of  pliers,  drawing  the  ends  together  over  the  face  of  the  stay 
instead  of  splitting  the  pins.  There  is  more  or  less  danger  of  splitting 
the  teeth  by  this  method  ;  besides,  the  cutting  of  four  leaflets  and  bending 
them  from  the  centre  gives  a  form  to  the  pin  like  that  of  a  rivet  head  : 
the  likeness  is  complete  when  the  spaces  between  the  leaflets  are  filled  with 
solder,  so  that  the  attachment  is  a  combination  of  soldering  and  riveting. 

No  matter  how  carefully  the  stay-fltting  may  be  done  by  this  method, 
there  is  not  so  good  an  adaptation  of  stay  to  tooth  as  with  the  first  method 
described.  Another  objection  is  that  the  necessary  manipulations  tend 
to  loosen,  to  a  greater  or  less  extent,  the  teeth  from  their  positions  in  the 
investment,  so  that  after  soldering  the  alterations  of  position  may 
become  evident. 

Dr.  W.  H.  Trueman  ^  advises  a  method  for  overcoming  one  of  the 
great  defects  arising  from  stay-fitting  in  the  soldering  investment — viz. 
the  want  of  accurate  contact  between  the  wings  of  the  stays  and  the 
lower  portions  of  the  tooth  back.  Each  stay  is  fitted  and  bevelled  as 
for  plain  teeth  with  straight  sides.  Narrow  pieces  of  thin  platinum 
plate  are  cut  extending  from  the  top  of  the  gum-joint  between  the  teeth 
to  the  plate,  and  wide  enough  to  be  firmly  held  by  the  sides  of  the  stay. 
Before  the  stays  are  fastened  to  the  teeth  these  pieces  are  pressed  across 
the  joints,  fitting  any  irregularities  of  form  which  may  be  present,  the 
stays  placed  in  position  in  pairs,  so  that  by  bending  down  the  pins 
the  sides  of  the  stay  hold  the  platinum  pieces  firmly  in  position.  When 
all  the  stays  have  been  adjusted  and  fastened  small  pieces  of  the  stay 
metal  are  bevelled  to  fit  between  the  sides  of  the  adjoining  stays,  and 
long  enough  to  hide  the  platinum  :  before  placing  them  for  soldering  the 
surface  of  the  platinum  is  covered  by  borax,  the  base  joints  are  scraped  ; 
the  small  sections  are  covered  by  the  flux  and  placed  in  position.  Should 
there  be  any  points  of  imperfect  contact  between  the  bases  of  stays  and 
the  plate,  the  space  is  to  be  perfectly  filled  with  small  pieces  of  plate 
appropriately  filed  and  fitted. 

Very  long  teeth,  those  subjected  to  unusual  stress  in  mastication,  and 
which  might  exhibit  a  tendency  to  bend  at  the  plate  joint,  are  given  the 

^  American  System  of  Dentistry,  vol.  ii. 
27 


418  SELECTING  AND  FITTING   THE  TEETH,   ETC. 

additional  rigidity  necessary  by  placing  at  the  base  of  each  joint  a  section 
of  triangular  wire.  A  cream  of  borax  is  applied  to  all  the  joints  and 
about  each  pin.  Solder  is  cut  into  small  squares  of  about  one-sixteenth  of 
an  inch  size  and  covered  with  borax.  Above  each  pin  and  over  each  lateral 
joint  one  of  these  squares  is  placed.  At  the  base  of  the  stays  a  continuous 
line  of  the  pieces  is  placed  on  the  plate.  This  amount  of  solder  should 
suffice  to  solder  a  denture  if  the  stays  have  been  accurately  fitted  and 
spaces  or  weak  joints  correctly  buttressed  by  means  of  additional  plate. 

The  following  rules  are  to  be  observed  in  soldering ; 

When  two  pieces  of  metal  are  to  be  united  by  solder  their  surfaces 
should  be  as  nearly  as  possible  in  perfect  contact. 

The  solder  used  for  dental  appliances  should  be  employed  merely  as 
a  uniting  agent,  and  beyond  the  amount  necessary  to  perform  this  office 
it  should  form  no  part  of  a  fixture.  Any  additional  strength  of  the  piece 
should  be  derived  from  additions  of  plate,  not  of  solder. 

Absolute  chemical  cleanliness  of  the  surfaces  to  be  united  is  neces- 
sary, for  soldering  is  a  molecular  union  of  the  surfaces  of  metals  by  means  of 
a  metal  of  greater  fusibility  than  those  to  be  united,  and  any  substance 
interposed  between  the  metallic  molecules  prevents  their  intimate  union. 

The  thickest  part  of  an  investment  is  to  receive  the  greatest  volume 
of  heat. 

Solder  flows  toward  the  parts  of  highest  temperature,  so  that  in  sol- 
dering the  part  into  or  over  which  solder  is  to  be  floAved  is  made  hotter 
than  its  ^  surroundings. 

The  nearer  a  metal  is  raised  toward  its  melting-point,  the  more  its 
molecules  separate,  and  it  tends  to  assume  a  crystalline  structure ;  there- 
fore the  higher  the  melting-point  of  the  solder  used,  the  stronger  is  the 
union  of  the  solder  with  the  soldered  metals,  and  the  tensile  strength  of 
the  latter  is  correspondingly  lessened. 

With  decrease  in  the  thickness  of  the  solder  pieces  there  is  an  in- 
creased surface  of  oxidation. 

Solder  should  be  placed  at  short  intervals  on  the  part  of  the  fixture 
most  difficult  to  heat. 

Drying  of  the  investment  should  precede  the  heating  of  it. 

No  tooth  should  receive  the  direct  flame  of  the  blowpipe  until  it  is 
heated  to  redness  by  heat  transmitted  through  the  investment  from  the 
exterior. 

Borax  must  not  be  placed  on  porcelain  :  it  forms  a  contractible  glass 
surface  which  in  contracting  produces  enamel  fracture. 

In  any  piece  where  there  may  be  several  soldering  operations  begin 
with  a  high-carat  solder — 18-carat  solder  for  18-carat  plate — the  second 
soldering  with  16-carat,  and  if  a  subsequent  one  be  required,  14-carat. 
This  is  not  necessary  where  the  heat  required  for  fusion  of  the  second 
solder  is  at  a  distance  from  the  solder  first  fused. 

Heating  and  cooling  should  be  gradual. 

The  case  is  now  set  in  the  base  of  an  old  vulcanite  flask  and  placed 
on  a  furnace,  and  warmed  until  the  investment  is  perfectly  dry  :  the  heat 
is  gradually  increased  until  the  base  of  the  investment  is  red  hot.  Trans- 
ferred to  a  Fletcher  furnace,  the  heat  is  increased  until  the  entire  piece 
is  at  a  low  red  heat.  While  the  last  stages  of  the  furnace-heating  are  in 
progress  a  soldering-pan  is  filled  with  small  pieces  of  charcoal  and  heated 


INVESTING   THE  CASE.  419 

under  a  blowpipe  (Figs.  68  and  71).  The  case  is  transferred  to  the  bed  of 
charcoal,  the  pieces  of  the  latter  being  heaped  about  the  sides  of  the  invest- 
ment. The  broad  blowpipe  flame  is  then  thrown  beneath  the  investment 
and  passed  rapidly  over  its  outer  wall,  until  the  teeth  and  stays  are  made 
red  by  the  transmitted  heat  and  the  solder  begins  to  settle.  The  fine 
flame  is  now  thrown  upon  the  line  of  junction  between  the  stays  and 
plate,  and  carried  from  the  terminal  molar  of  one  side  to  that  of  the 
other,  the  solder  melting  and  flowing  freely.  Usually  the  solder  above 
the  pins  and  lateral  joints  is  fused  by  the  same  flame  ;  if  not,  if  it  do  not 
flow  freely  about  the  pins  and  between  the  joints,  a  very  pointed  flame 
is  directed  at  each  pin  and  joint.  To  flow  as  it  should  the  solder  pji- 
hibits  a  quick  fluidity  and  has  a  smooth,  even  surface  at  the  completion 
of  the  operation.  The  case  is  now  returned  to  the  warm  tray  and  per- 
mitted to  cool  slowly.  When  the  stays  are  cooled,  this  is  the  test  for 
the  proper  time  of  removing  the  investment ;  the  latter  is  carefully 
broken  away  piecemeal.  The  teeth  and  gums  are  now  examined  for  any 
possible  cracks  or  checks,  as  they  are  more  readily  seen  while  the  case  is 
dry.  The  piece  is  boiled  in  the  acid  solution,  washed,  scrubbed  with 
soap  powder,  and  dried,  and  then  placed  on  the  model. 

If  the  preceding  operations  have  all  been  done  correctly,  the  plate 
will  have  suffered  no  change  of  form  and  the  porcelain  will  be  intact. 
If,  however,  there  have  been  any  neglect  of  the  minutiae,  all  of  vital  im- 
portance, the  plate  may  be  warped,  the  porcelain  gums  checked,  or  one 
or  more  teeth  cracked  or  in  malposition.  If  the  pieces  have  been  accu- 
rately fitted  and  no  excess  of  solder  used,  the  succeeding  operations  are 
a  comparatively  light  task,  but  none  the  less  important.  A  small  fine 
corundum  wheel  on  the  lathe  is  used  to  grind  down  the  heads  of  the 
pins  and  to  make  uniform  the  joint  at  the  bases  of  the  backing.  A 
wheel  should  never  be  used  when  and  where  it  touches  any  point  save 
the  one  upon  which  we  desire  to  operate.  Flat  and  half-round  gravers 
(Fig.  291)  are  employed  for  the  finishing  dressing  and  scraping.  The 
tops  of  the  joints  between  the  stays  are  given  a  uniform  concavity  by 
means  of  engine  burrs  of  the  plug-finishing  variety.  The  stays  them- 
selves and  the  plate  are  not  to  be  reduced  in  thickness  at  any  point :  for 
this  reason  tools  and  appliances  should  never  be  larger  than  necessary 
to  remove  the  superfluous  solder. 

It  is  a  prudent  measure  to  make  a  plaster  cast  of  the  interior  of  the 
plate  to  support  the  latter  during  the  trimming  and  buffing  operation  : 
by  this  means  there  is  a  lessening  of  the  danger  of  bending  the  plate  and 
of  undue  strain  upon  the  artificial  teeth.  Useful  points  for  the  smooth- 
ing of  the  surfaces  of  the  stays  and  their  joints  are  made  of  old  corun- 
dum wheels  softened  by  heat  and  drawn  out  into  flat  pencils.  By  alter- 
ing the  shapes  of  their  points  these  pencils  may  be  formed  so  that  they 
may  be  operated  in  any  irregular  places.  After  all  of  the  surfaces  have 
been  dressed  smooth,  water-of-Ayr  stones  are  used  to  give  the  final 
dressing  :  they  are  passed  over  every  portion  of  the  plate  surface,  oblit- 
erating all  of  the  tool-marks  and  removing  the  outer  coating  of  the  entire 
plate.  "  To  prevent  the  entrance  of  foreign  particles  in  the  spaces 
between  the  teeth  and  plate,  and  between  the  teeth  themselves,  the  den- 
ture may  be  warmed,  and  melted  paraffin  flowed  into  all  interstices :  this 
is  permitted  to  remain,  as  it  effectually  prevents  the  collection  of  debris 


420 


SELECTING  AND  FITTING  THE  TEETH,  ETC. 


and  secretions  in  parts  inaccessible  to  ordinary  cleansing  agents  "  (Bon- 
will).  The  piece  is  now  transferred  to  the  polishing  lathe,  where  the 
smoothing  is  completed  by  means  of  fine  felt  wheels  and  powdered 
pumice. 

It  is  customary  with  the  experienced  operator  to  dispense  with  the 
use  of  Scotch  stone,  except  in  places  inaccessible  to  the  following  imple- 
ment. Select  from  the  stock  of  the  dental-goods  dealer  the  hardest  of  the 
felt  cones  offered.  This  is  placed  on  the  mandrel  of  the  polishing  lathe 
and  revolved  rapidly,  when  a  sharp  knife-blade  held  against  it  divides 
it  into  wheels  of  any  desired  width.  A  section  of  this,  three-eighths 
of  an  inch  wide,  is  kept  constantly  charged  with  powdered  pumice  made 
into  paste  with  water,  and  is  passed  rapidly  across  all  parts  exhibiting 
scratches  or  tool-marks.  The  device  is  for  the  removal  of  slight  blem- 
ishes, and  should  never  be  applied  to  reducing  protuberances.  The  case 
is  held  with  the  fingers  embracing  the  outside  of  the  teeth  and  support- 
ing the  body  of  the  plate  firmly,  so  that  no  uneven  pressure  is  brought 
to  bear  upon  the  latter.  Plates  are  occasionally  warped  during  the  fin- 
ishing operation  if  held  improperly.  The  piece  is  kept  constantly  in 
motion,  so  that  while  buffing  there  shall  be  no  prolonged  contact  of  the 
wheel  at  any  point.  The  wheels  as  they  are  worn  down  are  preserved 
for  buffing  small  spaces.     When  the  surfaces  of  the  plate  and  stays  are 

perfectly  smooth,   the  edges  of  the 
Fig.  491.  plate  rounded  and  freed  of  all  minute 

irregularities,  a  brush  having  a  row 
of  stiff  bristles  is  a  substitute  for 
the  wheel :  this  is  passed  rapidly 
over  the  surfaces  of  plate  and  stays, 
cleansing  well  the  palatal  surface  of 
the  former,  but  removing  none  of  its 
fine  lines.  When  all  the  surfaces 
have  received  a  fair  polish  by  this 
means,  a  similar  brush  is  placed  on 
the  mandrel,  and  further  surfaced, 
using  a  paste  of  chalk  as  the  polish- 
ing medium.  Succeeding  this,  a 
broad  brush  (Fig.  97)  having  fine 
bristles  is  employed  with  the  chalk 
paste,  to  give  a  high  polish  to  all 
of  the  surfaces — a  sufficient  finish 
to  render  the  color  of  the  solder  undistinguishable.  The  plate  is  from 
time  to  time  washed  to  observe  the  progress  of  these  operations,  and, 
after  the  buffing  with  chalk  and  soft  wheel,  is  scrubbed  well  with  soap 
to  free  it  from  all  particles  of  pumice  or  chalk. 

A  practice  followed  by  the  writer,  but  which  appears  to  have  fallen 
into  general  disuse,  is  to  succeed  the  foregoing  operation  by  that  of 
burnishing. 

It  is  difficult  to  procure  an  effective  set  of  burnishers :  the  best  are 
of  small  points  and  edges  made  of  forged  steel,  the  temper  scarcely 
drawn,  and  given  a  mirror-like  polish  (Fig.  492). 

A  folded  towel  is  placed  before  the  operator  and  the  denture  laid 
upon  it,  and  beside  it  the  burnishers.     A  block  of  coarse  soap,  free 


Brush  wheel,  cup-shaped,  for  surfacing. 


SPIRAL  SPRINGS. 


421 


Fig.  492. 


Burnishers. 


from  any  grit,  and  a  vessel  of  water,  are  set  beyond,  so  that  the  blades  of 
the  burnishers  may  be  frequently  lubricated  by  dipping  them  first  in  the 
water,  then  rubbing  them  over  the 
soap.  The  burnishers  are  rubbed  over 
every  portion  of  the  plate  surfaces  and 
stays  until  a  brilliant  surface  is  given 
them.  This  operation  requires  half  an 
hour  or  more  to  do  thoroughly.  At 
its  completion  the  burnishers  are  dried 
and  rubbed  smooth  on  a  piece  of 
chamois,  and  returned  to  a  wash-leather 
wrapping  having  appropriate  pockets 
for  each  tool.  The  case  is  now 
washed  free  from  soap,  and  is  ready 
for  the  final  polishing.  The  burnish- 
ing is  commonly  dispensed  with,  and  the  succeeding  operation  practised 
immediately  after  the  final  buffing  with  whiting.  A  brush  four  inches 
in  diameter,  having  the  softest  of  bristles,  is  employed.  A  thin  mixture 
is  made  of  alcohol  and  the  finest  jeweller's  rouge  (an  oxide  of  iron) :  this 
is  painted  over  the  surfaces  of  the  plate  and  stays,  and  the  brush,  revolv- 
ing as  rapidly  as  possible,  is  passed  and  repassed  over  all  parts  until  the 
metal  portions  of  the  denture  have  a  polish  equalling  that  of  the  inner 
case  of  a  watch.  Every  trace  of  the  polishing  powder  is  removed  with 
soap  and  water. 

An  attractive  finish  may  be  given  the  palatal  surface  of  the  plate 
with  a  water-of-Ayr  stone.  A  piece  of  this  material  is  filed  to  a  pencil 
point ;  the  plate  surface  is  wet  and  the  entire  palatal  surface,  except  the 
interior  of  the  chamber,  which  is  highly  burnished,  is  marked  by  a 
series  of  spirals  traced  by  the  pencil  point,  the  lines  of  the  spirals 
radiating  from  the  edges  of  the  chamber :  it  gives  the  surface  of  the 
plate  the  appearance  of  frosting.  Any  rouge  remaining  about  the  joints 
which  is  not  removable  by  soap  and  water  may  be  destroyed  by  touching 
the  joints  with  nitric  acid,  then  reapplying  the  soap.  If  the  burnish- 
ing operation  have  been  followed,  it  will  be  found  that  the  polish  of  the 
plate  persists  for  a  greater  period. 

Spiral  Springs. 

Prior  to  the  advent  of  the  vacuum  chamber  formed  in  plates,  the 
retaining  appliance  employed  with  full  dentures  was  that  known  as  the 
spiral  spring.  Improvements  in  laboratory  technique,  comprised  in  bet- 
ter means,  methods,  and  materials  for  impression-taking,  together  with  a 
more  accurate  adaptation  of  plates,  have  so  limited  the  use  of  these 
springs  as  to  place  them  in  the  class  of  obsolete  appliances.  It  is  ex- 
tremely rare  that  recourse  to  this  method  of  retention  is  ever  necessary. 
Springs  are  employed  only  when  the  anatomical  configuration  of  the  parts 
would  render  the  employment  of  other  retaining  devices  inapplicable. 

Examples  of  such  cases  are  found  when  any  of  the  following  condi- 
tions exist :  Extreme  flatness  of  the  arch ;  extreme  contraction  of  the 
area  upon  which  the  plate  rests ;  an  exaggerated  softness  and  thickness 
of  the  soft  tissues  of  the  mouth ;  or  for  attachment  to  obturators  or 
artificial  vela  in  edentulous  cleft-palate  cases. 


422 


SELECTING  AND  FITTING   THE  TEETH,   ETC. 


Full  denture  with  spiral  springs  in  position. 


The  appliance  consists  of  two  parts — the  springs  and  the  arms  to 
which  they  are  attached.     The  springs  are  made  of  wire  coiled  about  a 

mandrel,  so  that  they  have  a  tubu- 
FiG.  493,  lar  form.     The  arms  are  in  two 

sections  :  one  section  is  anchored 
in  the  buccal  wall  of  the  denture  ; 
the  other,  freely  movable  upon  it 
by  a  swivel -joint,  is  at  right 
angles  to  the  first.  There  are 
four  of  these  double  arms — one 
for  either  side  of  each  denture. 
The  springs  are  in  pairs  —  one 
for  the  right,  one  for  the  left 
side. 

The  springs  are  slipped  over 
the  free  or  the  movable  arms, 
with  the  concavity  of  the  spring 
backward,  as  shown  in  Fig.  493. 
It  will  be  seen  that  the  elas- 
ticity of  the  spring  tends  to  press  both  dentures  in  their  proper  positions. 
They  are  so  attached  that  the  surfaces  of  the  springs  will  rest  upon  the 
buccal  aspects  of  the  denture,  and  not  protrude  in  such  a  manner  as  to 
irritate  the  soft  tissues  of  the  mouth. 

The  springs  are  made  of  round  platinous  gold  wire,  of  from  No.  24 
to  30  gauge,  wound  upon  a  mandrel  somewhat  smaller  than  the  movable 
anchorage  arm.  An  ordinary  knitting-needle  will  serve  as  a  mandrel. 
The  wire  is  to  be  wound  in  a  coil  upon  this  mandrel  in  such  a  manner 
as  to  have  a  uniform  tension  throughout  the  coils  ;  that  is,  the  spring  when 
completed  should  be  perfectly  cylindrical.  The  sj)rings  must  be  accu- 
rately paired  :  the  degree  of  elasticity  in  both  must  be  alike.  The  method 
of  making  them,  as  described  by  Dr.  Wm.  H.  Trueman,  is  as  follows  •} 

"  The  mandrel.  A,  is  attached  to  the  lathe  by 
Fig.  494.  its  enlarged  extremity,  B.    To  support  the  man- 

drel when  in  use  a  block  of  hard  wood,  jB,  two 
inches  long  by  one  inch  wide  and  half  an  inch 
thick,  is  arranged  as  follows  :  Lengthwise  of 
the  block  and  centrally  located  upon  its  upper 
surface  there  is  formed  a  groove,  C,  in  depth 
twice  the  diameter  of  the  mandrel  and  of 
width  sufficient  for  the  mandrel  to  fit  it  tightly. 
From  the  bottom  of  this  groove  and  about 
half  an  inch  from  one  end  drill  a  hole,  D, 
one-sixteenth  of  an  inch  in  diameter  through 
the  thickness  of  the  block,  countersinking  each 
end  sufficiently  to  remove  the  square  edge  and 
round  the  entrance  to  the  hole  at  each  side  of 
the  block.  With  a  small  round  graver  increase 
the  depth  and  width  of  the  groove  from  the 
hole  just  made  to  the  nearest  end  of  the  block,  as  seen  at  e.  The 
object  of  this  is  that  the  mandrel  may  be  evenly  supported  by  the 
^  American  System  of  Dentistry,  vol.  ii. 


Apparatus  for  making  spiral 
springs:  A,  mandrel;  B,  por- 
tion fitted  to  lathe ;  f,  loop  to 
■which  wire  is  fastened ;  B, 
block  supporting  mandrel ;  c, 
groove  in  which  mandrel 
turns  ;  d,  hole  through  which 
wire  p)asses ;  e,  enlarged  por- 
tion of  groove  to  accommo- 
date spring  wound. 


SPIRAL  SPRINGS.  423 

groove  in  the  block  when  the  portion  of  its  length  occupying  this  part 
of  the  groove  is  covered  by  the  wire  wound  upon  it. 

"  In  using  this  device  secure  the  mandrel  in  the  lathe  ;  the  small  lathe 
used  for  grinding  teeth  will  answer  if  a  stronger  one  is  not  available, 
as  the  power  required  is  but  slight.  Pass  one  end  of  the  wire  through 
the  hole  in  the  block  and  secure  it  to  the  loop,  r,  on  the  mandrel ;  turn 
the  mandrel  a  few  times,  guiding  the  wire  so  that  the  coils  will  be  far 
apart :  the  object  of  this  is,  first,  to  more  firmly  secure  the  wire  to  the 
mandrel ;  second,  to  occupy  the  space  upon  the  mandrel  corresponding 
to  the  space  between  the  end  of  the  block  and  the  hole  through  which 
the  wire  passes,  so  that  when  the  winding  begins  the  wire  will  be  drawn 
through  straight,  and  not  at  an  angle,  as  would  otherwise  be  the  case. 
This,  a  little  practical  experience  will  quickly  prove,  is  of  more  import- 
ance than  at  first  appears.  We  are  now  ready  to  begin  winding  the 
spring.  Place  the  end  of  the  block  through  which  the  wire  passes  next 
the  lathe-head,  the  mandrel  lying  in  the  groove  opposite  the  centre  of 
and  in  line  with  the  axis  of  the  lathe-spindle ;  the  right  hand  should 
hold  the  block  firmly,  and  the  fingers  of  the  left  hand,  protected  with  a 
glove  or  a  piece  of  cloth,  regulate  the  tension  of  the  wire  by  making  it 
bear  hard  against  the  side  of  the  hole,  d.  To  make  a  good  spring  the 
wire  should  be  held  firmly  and  with  a  greater  strain  than  would  be 
prudent  with  the  unprotected  fingers.  Slowly  turn  the  lathe,  increasing 
the  speed  if  the  winding  is  proceeding  satisfactorily,  and  keep  the  block 
firmly  pressed  toward  the  lathe-head,  so  as  to  lay  the  coils  closely 
together :  the  wire  forces  the  block  forward  on  the  mandrel  too  rapidly 
unless  resisted  by  a  firm,  steady  pressure.  There  are  several  points  to 
be  carefully  guarded  in  winding  a  spring.  It  is  all-important  that  the 
first  few  coils  should  be  laid  closely  together ;  they  are  apt  to  determine 
the  character  of  all  that  follow  :  it  may  be  necessary  before  proceeding 
to  force  them  together  with  a  burnisher  if  they  are  disposed  to  separate. 
See  that  the  wire  is  not. liable  to  become  entangled  in  the  lathe  or  with 
near  objects,  or  to  form  "  kinks,"  as  it  is  very  apt  to  do.  By  attaching 
to  the  free  end  of  the  wire  a  weight  of  a  few  ounces  this  annoyance  may 
be  avoided.  There  is  a  constant  tendency  in  the  coils  to  ride  over  those 
already  formed ;  this  must  be  checked  by  sufficient  tension.  If  the 
spring  is  a  long  one  or  if  the  fingers  are  insufficiently  guarded,  the 
friction  of  the  wire  passing  over  them  becomes  quite  painful,  naturally 
causing  the  tension  to  be  relaxed  and  spoiling  the  spring.  The  end  of  the 
wire,  if  the  wire  is  completely  used  up,  becomes  a  source  of  danger  as  it 
passes  through  the  block.  It  may  coil  around  a  carelessly-disposed  finger 
or  it  may  be  bent  into  a  hook ;  in  either  case  it  is  liable  to  do  serious 
injury.  This  will  suggest  that  if  a  weight  is  attached  to  it,  it  should 
be  secured  by  tying  with  a  piece  of  thread  that  will  either  slip  off  or 
break — never  by  making  a  hook  or  loop  in  the  wire." 

The  arms  are  made  of  18-carat  wire,  of  a  size  slightly  larger  than  the 
tube  of  the  springs.  Eight  pieces  of  wire  are  cut,  each  about  three- 
quarters  of  an  inch  long.  Four  of  these  pieces  are  to  be  made  into 
movable,  four  into  the  fixation,  arms.  For  each  of  the  latter  two  disks 
of  plate,  No.  24,  are  cut :  these  are  perforated  in  their  centres,  so  that 
they  shall  fit  tightly  over  the  wires.  One  of  the  disks  is  driven  on  the 
wire  for  about  one-eighth  of  an  inch  ;  the  second  is  then  placed  at  a 


424  SELECTING  AND  FITTING   THE  TEETH,  ETC. 

distance  from  the  first  slightly  less  than  the  diameter  of  the  wire.    The 

space  on  the  wire  between  these  disks  is  to  be  kept  free  of  the  borax 

with  which  the  lines  of  junction  of  wire  and  disk  are  touched.    An 

infinitesimal  portion  of  solder  is  placed  outside  each  disk 

Fig.  495.  and  fused,  attaching  the  pieces.     The  external  disk  is 

A         ■  ■     ID       rounded  and  smoothed ;  the  second  is  to  have  a  square 

edge. 

B  n  :Q  The  movable  arms  are  made  by  forming  the  ends 

Button  and  hook     of  the  wires  into  loops ;  the  loops  are  then  laid  upon 

^or  attaching  spi-     ^   smooth   anvil   and   flattened  until   they  are  narrow 

enough  to  pass   between  the  disks  on  the   first  arms. 

The  loop  is  opened  sufficiently  to  admit  the  section  of  wire  at  that  point. 

The  sides  of  the  movable  arms  are  squared  so  that  when  rotated  into 
the  spring  tube  a  faint  retaining  thread  will  be  formed  on  them. 

As  furnished  by  the  manufacturer  the  arms  are  undetachable  from 
one  another. 

If  the  plate  be  of  metal,  an  arm  is  to  be  soldered  to  the  stays  of  the 
artificial  teeth  ;  if  of  vulcanite  or  celluloid,  the  end  of  the  wire  is  bent 
into  a  retaining  loop.  When  the  plate  is  of  one  of  ihe  latter  materials, 
grooves  or  gutters  may  be  formed  in  its  buccal  wall  to  prevent  pressure 
of  the  spring  upon  the  tissues  of  the  mouth  (Fig.  493). 

The  arms  are  attached  to  the  dentures  in  such  positions  that  the  springs 
shall  rest  upon  the  buccal  surfaces  of  the  dentures.  The  arms  pass  be- 
tween the  second  bicuspids  and  first  molars  of  upper  and  lower  dentures. 
The  arms  are  passed  between  these  teeth  until  the  inner  disk  rests  upon 
their  buccal  surfaces.  The  springs  are  next  placed  over  the  movable 
arms  and  pressed  against  the  buccal  surfaces  of  the  artificial  teeth,  when 
the  arms  are  to  be  firmly  cemented  by  their  projecting  ends  to  the  palatal 
surface  of  the  plate  and  to  the  teeth.  When  the  cementing  adhesive 
wax  is  hard  the  springs  are  carefully  detached.  The  position  of  the 
arm  must  not  be  disturbed  in  any  subsequent  operation. 

Repairing  Soldered  Dentures. 

The  common  casualties  occurring  to  soldered  dentures  which  demand 
repair  are  cracks  of  the  plate,  the  fracture  of  one  or  more  teeth,  the  loss 
of  a  natural  tooth,  leaving  a  gap  in  the  arch,  and,  finally,  some  altera- 
tion of  the  form  of  the  plate. 

When  cases  present  for  repair,  it  is  always  to  be  noted  whether  there 
be  any  fault  in  the  adaptation  of  the  plate  to  the  arch  and  vault. 
Patients  by  becoming  accustomed  to  the  presence  of  a  denture  may  have 
their  mouths  grow  tolerant  of  a  piece,  the  adaptation  of  which  is  markedly 
faulty.  Much  chagrin  is  spared  the  operator  if  he  invariably  call  the 
patient's  attention  to  such  faults.  It  may  be  that  the  change  of  form  is 
due  to  resorption  of  the  tissues  of  the  mouth  producing  non-adaptation 
of  the  denture,  or  the  latter  itself  may  be  bent  from  its  original  form. 

The  operator  is  not  infrequently  annoyed  himself,  and  unjustly  cen- 
sured for  it  by  patients,  by  a  phenomenon  due  to  physiological  processes 
in  the  dental  arch  and  vault — to  wit :  an  artificial  denture  is  made  and 
faultlessly  adapted  ;  it  is  worn  by  the  patient  for  a  period  ranging  from 
one  to  several  years ;   then  gradually  develops  a  discomfort  which  an 


REPAIRING  SOLDERED  DENTURES.  425 

examination  shows  is  due  to  lack  of  adaptation  of  the  plate  to  its  base. 
When  placed  upon  the  original  plaster  model  it  is  seen  little  or  no 
change  of  its  original  form  has  occurred.  The  mouth  itself  has  altered 
in  its  configuration,  which  alteration  may  be  readily  demonstrated  to  the 
patient  by  placing  the  denture  upon  the  model.  This  is  one  of  the 
reasons  why  models  should  be  marked  with  the  patient's  name,  together 
with  the  date  of  making,  and  preserved.  These  changes  almost  always 
occur  in  the  mouths  of  all  patients  between  the  ages  of  twenty-five  and 
fifty  years. 

In  either  event,  the  difficulty  complained  of  being  faulty  adaptation, 
it  is  necessary  to  again  bring  the  plate  surface  in  contact  with  the  under- 
lying parts.  The  first  step  of  the  operation  is  the  securing  of  an  accu- 
rate plaster  impression,  from  which  a  perfect  model  is  obtained.  The 
latter  is  given  a  coating  of  varnish,  and  when  this  is  dry  the  denture  is 
set  on  the  model.  If  it  be  a  partial  case,  it  will  be  found,  frequently,  that 
it  is  impossible  to  place  the  piece  in  position  on  the  model  without  muti- 
lating the  plaster  teeth.  These  latter  are  for  the  time  removed,  and  the 
location  of  the  faults  of  adaptation  noted.  The  most  common  fault  will 
be  found  a  lateral  bending,  the  posterior  angles  of  the  plate  bent  away 
from  or  against  the  soft  tissues  of  these  parts.  If  this  be  the  only  dif- 
ficulty, the  experienced  workman  readily  and  deftly  restores  the  form  by 
bending  between  the  fingers.  If  the  difficulty  embrace  the  entire  vault 
or  outlined  spaces  of  it,  satisfactory  readjustment  is  only  possible  by 
reswaging  the  plate.  As  a  preliminary  measure  it  is  advisable  to  boil 
all  dentures  presented  for  repair  in  a  strong  solution  of  caustic  soda  or 
potash,  to  saponify  fatty  matters  and  destroy  all  food  deposits  between 
or  beneath  the  teeth.  If  this  precaution  be  not  taken,  the  deposits  are 
carbonized  during  the  soldering  operation,  and  blacken  the  joints  by  the 
insoluble  and  usually  irremovable  particles.  The  case  is  next  boiled  in 
the  acid  solution  to  free  it  of  the  oxides  on  its  surfaces. 

A  wax-bite  is  taken  and  an  articulator  formed.  If  it  be  a  partial 
denture  and  the  bases  of  the  stays  are  accessible  to  a  fine  saw-blade, 
each  tooth  is  removed  by  sawing  through  each  stay  as  close  to  the  plate 
as  possible.  Should  the  teeth  be  inaccessible  to  the  saw-blade,  a  small 
circular  saw  having  very  fine  teeth  is  mounted  on  the  lathe  and  em- 
ployed for  the  purpose.  In  some  cases  it  is  necessary  to  unsolder  the 
teeth  from  the  plate.  The  teeth  and  gums  are  covered  by  a  paste  of 
whiting  to  a  depth  of  about  one-quarter  of  an  inch  and  the  solder  sur- 
faces well  boraxed.  The  denture  is  set  over  a  stove  to  warm  sufficiently 
to  dry  the  paste  when  it  is  placed  in  a  furnace  and  heated.  It  is  now 
transferred  to  a  charcoal  bed,  leaving  the  teeth  and  gums  free  from  con- 
tact with  any  pieces  which  might  support  them.  A  blowpipe  flame  is 
directed  against  the  encasement  until  the  teeth  are  at  a  red  heat,  when  the 
flame  is  turned  against  the  plate  at  the  base  of  each  backing,  and  as 
soon  as  the  solder  is  fused  each  tooth  is  knocked  off  the  plate  and  into 
the  charcoal  bed,  where  it  is  permitted  to  lie  until  cool.  The  plate  is 
cleansed  in  acid,  and  the  rough  solder  masses  are  dressed  down  by 
means  of  coarse  files. 

The  plate  is  bent  into  as  close  an  adaptation  to  the  plaster  model  as 
possible,  between  the  fingers.  The  inner  surface  of  the  vacuum  chamber 
is  oiled,  and  in  it  is  fitted  a  piece  of  wax  of  the  same  depth  as  the  chamber 


426  SELECTING  AND  FITTING   THE  TEETH,  ETC. 

and  a  hair's-breadth  smaller  on  all  sides.  In  the  centre  of  the  chamber 
area  on  the  model  a  drop  of  melted  adhesive  wax  is  placed,  and  the  plate 
containing  the  wax  form  quickly  pressed  into  position.  In  a  minute  or 
two  the  plate  is  removed  and  the  edges  of  the  wax  form  are  pressed,  not 
melted,  into  contact  with  the  model ;  its  edges  are  next  smoothed  and 
bevelled,  and  the  entire  model  is  varnished.  A  die  is  made,  and  on  it  a 
counter-die  of  lead,  and  then  one  of  zinc,  are  formed.  Between  the  die 
and  lead  counter  the  plate  is  swaged,  interposing  between  the  counter-die 
and  plate  a  layer  of  the  wet  rubber  cloth  to  prevent  contamination  of 
the  surfa(ie  of  the  plate,  always  more  or  less  rough. 

The  plate  is  annealed,  and  then  swaged  between  the  zinc  die  and 
counter,  when  usually  it  will  be  found  to  have  a  satisfactory  adaptation 
to  the  model.  The  teeth  are  boiled  in  acid,  any  ragged  edges  of  solder 
dressed  ofP,  and  are  adapted  to  the  model  and  articulator  as  for  a  new 
case.  The  teeth  are  cemented  to  the  plate,  tried  in  the  mouth,  and,  if 
found  correct,  the  piece  is  invested. 

Any  space  between  the  bases  of  the  stays  and  the  plate  are  to  be 
filled  with  pieces  of  plate.  The  surfaces  to  be  soldered  are  first  covered 
by  the  cream  borax ;  then  in  the  spaces  beneath  the  teeth  and  stays  a 
piece  of  pure  gold  is  placed  as  a  matrix ;  a  fragment  of  24-carat  plate. 
No.  36,  being  bent  upon  itself,  and  the  folded  edge  introduced  beneath  the 
tooth  :  the  leaflets  are  then  separated,  one  being  brought  in  contact  with 
the  base  of  the  tooth,  the  other  with  the  plate  :  the  V-shaped  depression 
is  filled  flush  with  small  bars  of  plate.  The  stays  and  additions  are 
covered  by  the  borax,  a  greater  amount  than  usual  of  solder  placed  on 
the  plate  beneath  the  stay,  and  the  case  is  heated  and  soldered  as 
described  on  the  preceding  pages. 

The  next  class  of  repairs  in  point  of  extent  are  those  which  require 
the  addition  of  plate  to  overlie  spaces  left  by  the  loss  of  a  natural  tooth 
or  teeth.  A  plaster  impression  is  taken  of  the  part  with  the  denture  in 
position  in  the  mouth.  The  plate  is  to  be  withdrawn  in  the  impression. 
A  wax-bite,  which  has  also  been  taken  with  the  plate  in  the  mouth  and 
before  taking  the  impression,  is  mounted  and  an  articulation  made.  If 
the  break  in  the  outline  be  small  and  of  regular  form,  a  die  is  not  re- 
quired to  fit  the  additional  pieces.  Tlie  edges  of  the  plate  surrounding 
the  break  are  to  be  bevelled  from  the  palatal  side.  If  the  edges  of  the 
break  be  more  than  one-sixteenth  of  an  inch  from  contact  with  the 
model,  a  series  of  saw-cuts  are  made  along  it,  extending  into  the  plate 
halfway  to  the  line  of  contact  with  the  model.  A  thin  piece  of  24-  or 
22-carat  gold  plate  or  of  platinum  is  annealed,  and  made  to  conform  to 
the  surface  of  the  model  by  means  of  the  rubber  end  of  a  lead  pencil : 
its  inner  edge  is  to  come  within  the  plate  line  as  far  as  the  end  of  the 
bevel,  its  outer  edge  to  be  on  a  line  with  the  plate  line. 

A  joint  made  between  the  plate  and  the  supplementary  piece  is 
stronger  when  the  edges  of  the  plate  overlap  the  patch :  the  adap- 
tation is  more  accurate,  and  to  secure  the  necessary  strength  it  is  not 
required  to  leave  an  unsightly  protuberance.  The  leaflets  between  the 
small  saw-cuts  are  now  bent  down,  covering  the  added  piece.  The  tooth 
or  teeth  are  fitted  to  their  places,  and  stays  made.  The  several  pieces 
are  cemented  together,  and  the  fixture  is  invested,  making  the  invest- 
ment immediately  underlying  the  plate  joint  thinner  than  at  other  places. 


BEPAIBING  SOLDERED  DENTURES.  427 

SO  that  more  heat  will  be  transmitted  to  this  portion  of  the  denture.  The 
cement  is  picked  away,  the  surfaces  well  covered  by  a  cream  of  borax, 
and  in  the  space  between  the  stay  and  the  plate  edge  surrounding  the 
break  a  piece  of  plate  of  No.  26  gauge  is  set,  fitting  the  piece  beneath  it. 
Solder  is  placed  around  the  joints  and  the  case  well  heated.  In  the 
soldering  the  heat  is  to  be  thrown  upon  the  plate  beyond  the  line  of 
the  break,  so  that  the  solder  may  be  drawn  beneath  the  plate  and  fill  the 
joint.  The  deflected  heat  usually  flows  the  solder  about  the  pins  of  the 
teeth  and  at  the  base  of  the  stay. 

Should  the  space  to  receive  the  addition  be  large  or  have  an  irregular 
form,  it  is  advisable  to  swage  the  piece.  The  plate  edges  adjoining  the 
open  space  are  to  be  bevelled,  and  the  line  of  the  edges  traced  on  the 
model  by  means  of  a  pin  point.  The  plate  is  removed  from  the  model, 
the  latter  is  varnished,  and  a  small  die  made  of  the  part  to  be  covered 
by  plate.  A  piece  of  plate  of  No.  26  gauge  is  swaged  to  fit,  and  its 
inner  edge  cut  down  until  it  is  slightly  broader  than  the  pin  scratch  on 
the  model.  Saw-cuts  are  made  in  the  plate  edges  surrounding  the  break, 
and  the  leaflets  bent  down,  holding  the  swaged  section.  The  teeth  are 
mounted  and  the  pieces  united  as  described. 

Occasionally  it  is  necessary  to  make  the  repair  in  two  operations.  It 
may  be  impossible  to  perfectly  unite  the  piece  to  the  plate  and  the  tooth 
to  both  in  one  soldering.  Such  cases  are  found  in  those  having  a  portion 
of  the  joint  between  the  supplementary  piece  and  the  plate  extend  far 
beyond  the  palatal  edge  of  the  artificial  tooth  ;  for  instance,  where  it  is 
required  to  add  an  extension  to  the  end  of  a  lower  plate,  the  additional 
piece  being  virtually  a  small  plate  covering  the  ridge.  In  such  cases 
the  piece  is  first  swaged,  fitted,  and  soldered  to  the  plate,  and  the  tooth 
or  teeth  mounted  in  a  second  operation. 

A  common  casualty,  as  noted  above,  is  a  crack  in  some  portion  of  the 
plate.  Such  breaks  are  to  be  repaired  by  the  addition  of  a  strip  of  plate, 
never  by  solder  alone.  The  case  is  cleansed  thoroughly  and  the  edges 
of  the  crack  are  brought  together.  Should  the  edges  of  the  crack  be 
separated  more  than  about  one-twentieth  of  an  inch,  it  is  inadvisable  to 
attempt  readjustment  of  the  edges  :  the  repair  is  to  be  made  then  with- 
out any  bending.  The  crack  is  filled  with  the  cream  borax.  When  this 
is  dry  the  plate  is  invested,  and  a  piece  of  plate  of  No.  28  gauge,  about 
a  quarter  of  an  inch  wide  and  extending  the  full  length  of  the  crack,  is 
fitted  to  the  plate  covering  the  crack.  Its  upper  edges  are  bevelled,  and 
it  is  well  cleansed,  and  the  surfaces  to  be  united  covered  by  the  flux.  A 
piece  of  solder  is  laid  at  each  edge,  and  the  case  is  heated  and  soldered : 
in  finishing  the  strip  is  to  represent  a  rounded  ridge.  Should  the  crack 
be  at  the  portion  of  a  plate  embracing  the  neck  of  a  natural  tooth,  a  semi- 
lunar piece  is  to  be  fitted  over  the  plate  and  soldered  to  it. 

When  teeth  are  broken  from  a  denture  an  impression  is  taken  with 
the  plate  in  the  mouth,  an  articulation  made,  the  tooth  fitted,  stayed,  and 
soldered  as  with  a  new  case. 

If  the  tooth  be  broken  away  from  its  stay  and  lost,  the  repair  may  be 
made  by  riveting.  A  tooth  of  the  same  mould  and  color  is  selected,  the 
pin-holes  drilled,  not  punched  out,  as  the  latter  operation  invariably 
bends  the  stay.  The  tooth  is  ground  into  position  :  this  operation  will 
require  some  care,  owing  to  the  pins  hampering  the  free  mobility  of  the 


428  SELECTING  AND  FITTING   THE  TEETH,  ETC. 

tooth  in  its  space.  If  necessary,  the  pin-holes  may  be  reamed  out  and 
made  larger.  If  there  be  any  marked  difference  in  the  situations  of  the 
pins  of  the  new  tooth  from  those  in  the  old  one,  the  pin-holes  are  sawn 
into  elliptical  openings,  and  when  the  tooth  is  fitted  the  pins  are  so  bent 
as  to  cover  as  much  of  the  openings  as  possible.  The  case  is  then 
invested  and  soldered. 

Should  the  other  teeth  of  the  denture  be  of  such  type  as  would  be 
endangered  by  the  heating  necessary  in  soldering,  it  is  advisable  to  rivet 
the  tooth  to  the  stay.  A  tooth  is  selected  having  the  pins  at  the  same 
distance  apart  as  in  the  old  tooth.  The  pins  of  the  old  tooth  are  care- 
fully drilled  out  of  the  stay,  and  holes  are  countersunk  at  the  palatal 
side.     The  tooth  is  fitted  to  position,  and  the  pins  cut  off  to  about  one- 

FiG.  496. 


Riveting  hammer. 

sixteenth  of  an  inch  from  the  surface  of  the  stay.  A  folded  towel  is 
laid  upon  an  old  counter-die,  the  tooth  to  be  riveted  set  upon  the  towel, 
and  no  other  tooth  should  press  hard  against  the  latter  :  repeated  light 
blows  of  a  small  riveting  hammer  are  directed  against  the  ends  of  the 
pins  until  each  is  forged  into  the  countersinks,  filling  them  completely 
and  leaving  rounded  heads,  which  are  then  burnished  hard  to  complete 
the  operation. 

Cases  will  occasionally  present  in  which  the  artificial  tooth  has  broken 
away  from  its  stay,  leaving  pins  projecting  from  the  back  of  the  tooth 
about  one-fiftieth  of  an  inch  long.  Such  a  tooth  is  to  be  boiled  in  a  test- 
tube  with  nitric  acid.  To  its  back  is  burnished  a  covering  of  platinum 
plate.  No.  36  or  38.  Apertures  are  made  over  the  stumps  of  the  pins.  The 
tooth  and  the  platinum  back  are  invested,  a  piece  of  pure  gold  is  placed 
over  each  pin,  and  the  platinum  is  soldered  to  the  pins.  The  old  pins 
are  drilled  out  of  the  stay  standing  on  the  plate.  The  back  of  the  stay 
is  scraped  to  cleanse  and  thin  it,  and  its  top  bent  inward  slightly.  The 
tooth  with  the  platinum  back  is  set  against  the  stay  and  cemented  to  it : 
the  case  is  invested,  and  the  platinum  soldered  to  the  stay,  using  a  low- 
carat  solder. 

In  repairing  cases  having  a  gum  of  one  of  the  vegetable  bases,  if 
the  stay  be  standing  the  following  method  is  frequently  applicable  : 
The  rubber  or  celluloid  is  cut  out  to  receive  the  neck  of  the  tooth,  but 
the  festoon  covering  the  latter  is  to  remain  untouched.  A  plain  tooth  is 
fitted  to  the  stays,  in  which  pin-holes  have  been  drilled  and  countersunk. 
Phosphate  of  zinc  colored  pink  with  carmine  is  placed  in  the  depression 
cut  in  the  gum,  and  the  tooth  pressed  into  position  :  when  the  cement 
has  set  the  pins  of  the  tooth  are  riveted  as  described. 

To  properly  adjust  broken  or  detached  clasps  it  is  necessary  to  take 
an  impression  of  the  clasp  tooth  with  the  plate  in  the  mouth.  Should 
the  clasp  itself  be  broken,  the  surface  on  either  side  of  the  break  is  filed 


REPAIRING  SOLDERED   DENTURES.  429 

flat  and  a  piece  of  thin  clasp  metal  extending  for  one-fourtli  of  an  inch 
on  either  side  adapted,  cleansed,  and  perfectly  joined  to  the  clasp  by 
means  of  solder. 

A  method  of  repairing  metallic  plates  without  subjecting  the  denture 
to  the  soldering  operation,  and,  what  may  be  more  important,  a  means 
of  attaching  a  clasp  to  a  plate  or  an  additional  tooth  without  depriving 
the  patient  of  the  piece  except  for  a  few  minutes,  has  been  devised  by 
Prof.  C.  J.  Essig. 

A  typical  application  of  the  method  will  illustrate  its  advantages :  A 
patient  is  wearing  a  partial  gold  plate ;  one  of  the  remaining  natural 
teeth  is  becoming  progressively  looser,  and  may  be  lost  at  any  time ;  it 
is  not  permissible  to  deprive  the  patient  of  the  piece  for  the  length  of 
time  necessary  to  repair  it  by  soldering.  A  bite  and  impression  are 
taken  with  the  plate  in  position.  If  the  operation  be  the  preparation  of 
an  artificial  tooth  to  be  substituted  for  a  loosening  natural  organ,  as  soon 
as  it  is  removed  ;  the  plaster  tooth  on  the  model  is  cut  away,  together  with 
an  amount  of  plaster  to  represent  the  condition  of  the  soft  parts  after 
extraction.  A  die  and  counter-die  are  made,  and  a  piece  of  plate  No. 
26  is  swaged  which  shall  overlap  the  plate,  as  shown  on  the  model,  for 
one-fourth  of  an  inch  or  more  :  a  tongue  to  extend  into  the  interdental 
space  is  to  furnish  a  support  to  the  artificial  tooth.  An  articulating 
model  is  made,  a  tooth  fitted  to  the  model,  and  a  stay  adapted  to  it.  The 
pieces  are  now  invested  and  united  by  means  of  solder,  then  finished. 
The  edges  of  the  plate  piece  should  receive  a  bevel,  so  that  there  shall 
be  no  abrupt  line  between  the  new  and  old  plate. 

To  add  a  clasp,  an  impression  is  taken  with  the  plate  in  position,  and 
a  model  is  made  which  shall  have  a  perfect  representation  of  the  tooth  to 
be  clasped.     The  clasp  is  fitted  to  the  tooth,  and  a  piece  of  plate  to  the 
general  plate,  as  described  above.     This  is  filed  away 
about  the  base  of  the  clasp  tooth  until  it  has  a  close  Fig.  497. 

joint  with  the  clasp,  to  which  it  is  cemented,  invested, 
and  soldered,  and  finished  as  described. 

To  add  these  pieces  to  the  plate,  three  holes  are 
drilled  through  the  plate  as  marked  in  Fig.  497,  and 
each  is  countersunk  upon  its  upper  side.    When,  in  the 
first  instance  noted,  the  natural  tooth  is  lost,  or,  in 
the  second,  the  clasp  addition  is  prepared,  the  piece  is 
placed  in  the  mouth  with  the  plate  itself  in  position, 
and  by  means  of  a  sharp  excavator  point  the  outlines 
of  the  supplementary  piece  are  scratched  on  the  plate 
proper.     With  the  pieces  held  in  close  apposition  a 
drill  is  placed  through  the  openings  made  in  the  small  plate,  and  the 
plate  proper  perforated  :  the  holes  are  countersunk  at  the  palatal  surface. 
Gold  pins  upon  which  rivet  heads  have  been  formed  are  placed  through 
the  openings  and  riveted,  thus  holding  the  sections  firmly  together. 


CHAPTER  XIL 

ENGLISH  TUBE  TEETH:    THEIR  USE  IN  PLATE-,  CROWN-, 
AND  BRIDGE-WORK.i 

By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 


English  Tube  Teeth. 

The  English  tube  tooth  diifers  from  the  ordinary  plate  tooth  in  that 
its  attachment  to  the  piece  to  which  it  is  adjusted  is  effected  by  means 
of  a  central  tube  of  platinum  running  through  the  body  of  the  tooth,  and 
into  it  a  pin  or  post  is  introduced  (Figs.  498  to  500). 

Tube  teeth  may  be  used  in  any  situation  on  either  upper  or  lower 
plates,  and  they  are  well  adapted  for  mastication.  Being  somewhat 
cubical  in  shape,  they  are  probably  stronger  than  flat  teeth.  The  tube 
tooth  is  supported  over  its  whole  lower  surface,  and  the  greatest  strain" 
in  occlusion  falls  mostly  in  a  vertical  direction,  upon  the  crown  and 
parallel  to  the  line  of  the  central  pin  ;  whereas  in  a  flat  tooth,  the  attach- 
ment being  on  one  side  only,  the  strain  caused  by  the  impact  of  the  bite 
is  more  unevenly  distributed. 

The  tube  teeth  allow  of  easy  removal  for  repair,  it  being  possible  to 
add  a  new  tooth  in  from  ten  to  twenty  minutes. 

As  the  quantity  of  solder  used  in  uniting  the  backings  of  flat  teeth  to 
the  plate  is  of  necessity  considerable,  the  danger  of  warpage  from  this 
cause  is  proportionally  great.  By  the  use  of  tube  teeth  this  risk  is 
entirely  removed — a  consideration  which  alone  seems  sufficient  to  com- 
mend their  application  in  many  cases  back  of  the  cuspids,  where  flat-back 
masticating  teeth  would  otherwise  be  used. 

Many  English  dentists  claim  that  tube  teeth  are  more  adaptable  than 
pin  teeth  :  a  very  long  tooth  can  be  cut  down  to  any  length,  and  the 
body,  being  of  the  same  texture  throughout,  can  be  ground  and  polished 
perfectly. 

They  can  be  used  for  plate-,  crown-,  and  bridge-work,  and  in  some 
cases  in  combination  with  vulcanite.  From  the  ease  with  which  they 
may  be  adapted  a  small  stock  of  these  teeth  will  meet  all  ordinary  de- 
mands of  private  practice — a  most  important  consideration  to  practi- 
tioners who  are  not  within  easy  reach  of  a  dental  depot. 

Being  a  more  faithful  reproduction  of  the  shapes  of  natural  teeth, 
they  are  likely  to  feel  more  comfortable  to  the  tongue  and  interfere  with 
speech  less  than  do  flat  teeth. 

They  are,  in  all  probability,  more  easily  kept  clean,  being  without 
backings,  which  favor  the  lodgement  of  decomposable  material,  than  or- 

1  From  a  paper  read  before  the  World's  Columbian  Congress  by  John  Girdwood, 
L.  D.  S.  (E.  D.),  D.  D.  S.  (University  of  Pennsylvania). 
430 


ENGLISH  TUBE  TEETH. 


431 


dinary  pin  teeth,  and  their  supports,  being  surrounded  by  porcelain,  are 
out  of  the  reach  of  any  impurity  (Figs.  495  to  500). 


Fig.  498. 

Incisors. 

Defective.    Improved. 


Fig.  499. 
Bicuspid. 


Side. 


Plan. 


Side. 


Side. 


Side. 


Plan.  Plan. 

Defective  and  improved  tubing. 


Plan. 


For  crown-  and  bridge-work  many  advantages  are  claimed  for  tube 
teeth,  and  those  who  constantly  use  them  find  that  they  can  be  as 
perfectly  and  directly  fitted  to  natural  roots  as  any  other  form  of  porce- 
lain crowns.  Being  made  of  porcelain  with  but  a  thin  central  platinum 
tube  baked  in  them,  they  retain,  when  mounted  for  wear  in  the  mouth, 
their  translucency  and  natural  appearance — qualities  so  often  destroyed 
by  the  gold  backing  on  flat  teeth. 

There  seems,  however,  to  be  one  defect  in  the  tube  incisors  and  cus- 
pids as  at  present  manufactured.  In  these  the  base  is  frequently  too 
small  antero-posteriorly,  and  consequently  in  many  cases  it  is  impossible 
to  cover  the  root  completely  with  them.  Moreover,  the  tube  is  very  often 
too  near  the  front,  so  that  the  axis  of  the  crown  does  not  always  corre- 
spond with  that  of  the  root  (Fig.  498,  A). 

The  bicuspids  and  molars,  however,  are  free  from  any  such  faults, 
and  are  pre-eminently  well  adapted  for  crown-work.  Yet  with  the  front 
teeth  as  now  manufactured  good  work  can  be  done,  and  if  this  style  of 
teeth  were  in  greater  demand  manufacturers  would  probably  produce 
improvements  beyond  those  at  present  thought  necessary. 

The  setting  of  tube  teeth  requires  the  use  of  a  special  set  of  simple 
hand  tools,  which  are  shown  in  Figs.  501  to  507. 

Fig.  501,  a  countersinker  for  clearing  away  the  burr  which  forms 
upon  the  end  of  the  tube  when  ground,  and  for  slightly  enlarging  the 
orifice  of  the  tube  at  its  base.  A  suitable  countersinker  may  be  made 
from  an  old  excavator  handle  ground  to  a  three-sided  pyramidal  point 
and  tempered  hard.  It  should  be  large  enough  to  obviate  any  danger 
of  forcing  it  into  the  tube  and  so  vSplitting  the  tooth. 

Fig.  502,  a  tube-file  used  to  remove  the  debris  from  the  tube  after 
grinding :  it  follows  the  countersinker,  and  is  used  before  trying  the 
tooth  on  the  pin. 

Fig.  503,  a  marker :  this  is  a  piece  of  straight  round  wire  which 
should  fit  the  tubes  easily,  but  not  loosely,  and  have  one  end  filed  almost 
to  a  central  point. 

Fig.  504,  a  pair  of  flat-pointed  pliers  with  a  longitudinal  groove  in 
them  for  holding  the  pin  while  it  is  inserted  in  its  socket  in  the  plate. 


432 


ENGLISH  TUBE  TEETH,   ETC. 


Fig.  505,  a  sharp-pointed  graver. 

Fig.  506,  a  length  of  gold  pin  wire  (magnified). 


Fig.  501. 


Fig.  502. 


Fig.  503. 


Countersinker. 


Tube-file. 


Roughing  pliers,  with  gold  pin 
ready  for  insertion. 


Fig.  507,  a  pot  of  paint,  not  too  thin,  made  by  mixing  olive  oil  and 
vermilion. 

The  uses  of  these  instruments  will  be  described  in  the  explanation 
of  the  method  of  mounting  the  teeth  for  which  they  are  required. 


Fig.  505. 


Fig.  507. 


Sharp-pointed  graver. 
Fig.  506. 

Length  of  pin  wire. 


Pot  of  vermilion  and  brusli  for  mark- 
ing and  fine  filling. 


Fig.  508.  For  the  purpose  of  illustration  we  will  suppose  a  case  of 
a  partial  gold  upper  denture,  where  the  lateral  incisor  and  cuspid  on  the 
right  side  and  all  the  grinding  teeth  on  both  sides,  except  the  second 
superior  upper  molar,  are  absent.  Having  swaged  and  fitted  (Fig.  508) 
the  plate  in  the  ordinary  way  and  adjusted  the  clasp,  a  tube  tooth  is 
selected  for  each  side.  Care  must  be  taken  that  the  teeth  chosen  shall 
be  longer  than  is  apparently  necessary,  so  that  there  will  be  tooth-sub- 
stance to  spare  in  fitting  to  the  plate  and  bite.  The  teeth  are  now 
roughly  fitted  in  the  positions  they  will  occupy.  The  countersinker 
removes  the  burr  from  the  platinum  tube  at  its  ground  end,  and  the 


ENGLISH  TUBE  TEETH. 


433 


tube-file  clears  out  all  debris  from  end  to  end.     The  teeth  are  replaced 
on  the  plate  to  be  fastened  in  their  proper  positions  with  hard  wax. 


Fig.  508. 


Fig.  509. 


M  )c1l1  show  111^  ^t  uidin-;  tteth 


Plate  and  pms  for  post  teeth 


The  marking  wire,  tipped  with  vermilion  paint,  is  then  passed  down 
each  tube  till  it  touches  the  plate,  where  it  will  leave  a  mark  showing 
the  places  at  which  the  holes  are  to  be  drilled  to  receive  the  pins.  The 
teeth  are  then  removed  from  the  plate,  care  being  taken  to  avoid  dis- 
turbing the  color  mark.  With  a  sharp-pointed  graver  a  slight  pit  is 
made  for  the  drill.  The  plate  need  not  be  taken  from  the  model  while 
drilling  the  holes  for  the  pins :  care,  however,  must  be  observed  to  keep 
the  drill  exactly  at  the  same  angle  as  was  made  by  the  marker  (Fig. 
510).     By  means  of  a  broach  the  holes  in  the  plate  should  be  enlarged 

Fig.  510. 


Showing  method  of  marking  pin-posts. 

till  they  are  nearly,  but  not  quite,  large  enough  to  receive  the  pin-wire : 
the  rough  edge  or  burr  left  by  the  drill  must  be  removed  by  counter- 
sinking both  sides.  A  suitable  length  of  gold  pin-wire  should  then  be 
cut,  and  the  end  which  is  to  fit  the  socket  in  the  plate  should  be  slightly 
tapered,  so  as  to  fit  tightly  and  project  about  a  sixteenth  of  an  inch 
through  on  the  palatal  surface.  A  slight  groove  should  be  made  longi- 
tudinally on  the  tapered  end  of  the  wire  for  the  purpose  of  assisting  the 
solder  to  run  more  readily  from  the  palatal  to  the  lingual  surface.  The 
tapered  end  of  the  pin  and  the  pin-hole  are  then  touched  with  borax, 
and  the  wire  fixed  firmly  in  place  by  means  of  the  pliers  (Fig.  504), 
attention  being  paid  to  its  direction.  The  tooth  is  next  tried  on,  and, 
having  ascertained  that  this  particular  point  is  correct,  the  pins  may  be 
soldered  in  a  manner  to  allow  the  solder  to  flow  through  from  side  to 

28 


434  ENGLISH  TUBE   TEETH,   ETC. 

side.  It  is  not  necessary  to  invest  the  plate  for  this  purpose,  for  the 
tightness  of  the  pin  in  its  socket  will  support  it  sufficiently.  In  solder- 
ing it  is  of  the  utmost  importance  that  the  smallest  possible  quantity  of 
solder  be  used.  It  will  be  at  once  seen  that  as  the  tube  tooth  fits  the 
pin  exactly,  any  excess  of  solder  at  its  base  must  prevent  the  tooth's 
touching  the  plate,  unless  the  former  be  ground  out  or  the  superfluous 
solder  cut  away.  AVhen  the  plate  has  cooled,  the  flux  is  removed  by 
boiling  in  water  acidulated  with  sulphuric  acid.  The  projecting  end  of 
the  pin  should  then  be  cut  off,  and  smoothed  down  with  a  corundum  wheel 
and  graver  until  it  is  level  with  the  plate.  The  plate  is  then  replaced 
on  the  model  and  the  pin  filed  down  until  they  accurately  fit  the  bite. 
That  this  shortening  should  be  carefully  done  is  of  some  consequence, 
because  when  the  tooth  is  put  in  position  on  its  pin  it  can  be  seen  at  a 
glance  how  much  of  its  length  may  be  safely  ground  away  in  fitting. 
The  teeth  are  then  placed  on  the  pins,  and  if  the  latter  should  have 
tilted  in  soldering,  it  will  be  at  once  seen,  and  may  be  corrected  by 
grasping  the  pin  close  to  the  plate  and  bending  as  required.  Now  comes 
the  fine  fitting  of  the  teeth,  done  best  with  small  wheels :  Paint  is  placed 
upon  the  plate  where  the  tooth  will  touch  it,  and  the  latter  is  pressed 

gently   to   place :   when   removed   it  will 
I^'JG.  511.  show  a  small  red  mark  where  it  is  too  long 

0and  needs  grinding  off:  having  used  the 
|*n|  I™!       countersinker  and  tube-file,  the'  tooth  is  to 
\J  ^'^       be  tried  on  its  pin  again,  and  this  process 
I I        I  of  alternate  trying  on  and  grinding  is  to 

el,    Jl  -^    "*^      be  repeated  until  a  perfect  fit  is  obtained. 
^^     It  is  well  in  fitting  to  the  plate  to  remem- 
^^^^^=^-^^        ber  the  bite ;  otherwise  the  operator  will 
.     ,.  ,   ^    ^,  find,  to  his  annoyance,  after  havinp-  care- 

Plate  and  pms,  with  little  teeth  r>  n       r«,,     t    ,i        ,       ,i      ,i     ,  ,•      i    ,• 

ready  for  fixing.  lully  fitted  the  tootii,  that  ou  articulating 

it  is  too  short.  The  coronal  surfaces  of 
the  teeth  are  now  to  be  ground  to  suit  the  occlusion  of  the  bite,  using 
the  vermilion  paint  to  ascertain  points  of  undue  contact.  Next  the 
cuspid  and  first  bicuspid  on  the  right  side  are  set  and  finished,  the  first 
bicuspid  on  each  side  serving  as  a  guide :  the  pins  for  the  remaining 
teeth  may  be  inserted  at  one  soldering. 

Fig.  511.  Let  us  presume  that  all  the  teeth  have  been  fitted  to  the 
plate  and  to  the  bite  :  their  ground  edges  should  then  be  lightly  touched 
against  the  side  of  a  very  fine  corundum  or  Arkansas  wheel  in  the  direc- 
tion opposite  to  its  motion.  The  teeth  are  then  polished,  and  the  coronal 
ends  of  the  pins  are  finished  to  show  a  rounded  end  or  ground  to  the  bite 
according  to  the  requirements  of  the  case.  This  done,  the  plate  is  finished 
in  the  usual  manner.  Previous  to  fixing  the  teeth  a  few  shallow  cuts  are 
made  in  each  pin  with  a  fine  file.  When  the  teeth  have  been  properly 
cleaned  and  freed  from  all  traces  of  oil — which  can  be  done  by  boiling 
them  for  a  few  minutes  in  a  strong  solution  of  soda — their  tubes  are 
dried  by  cotton  wound  round  a  broach  and  their  interiors  roughened  by 
a  clean  tube-file.  Fig.  512  is  a  good  representation  of  how  the  tubes  are 
filled  with  sulphur.  This  material  is  melted  in  the  small  porcelain  Ber- 
lin cup  marked  A,  until  it  is  quite  fluid,  and  is  kept  in  this  condition 
and  held  by  an  assistant.     The  operator  himself  grasps  the  plate  firmly 


ENGLISH  TUBE  TEETH. 


435 


with  the  pliers  (Fig.  512)  in  the  left  hand  and  heats  the  whole  carefully 
over  the  lamp.  This  must  be  done  gradually,  and  the  flame  ought  not 
to  play  on  the  porcelain.     In  the  right  hand  he  takes  the  wire  spatula 


Fig.  512. 


Mode  of  grasping  plate  in  finally  fixing  teeth. 


-B  (Fig.  512),  and,  dipping  it  in  the  molten  sulphur,  conveys  it  to  the 
heated  plate  and  teeth  repeatedly  till  a  surplus  begins  to  show  itself. 
The  sulphur  runs  by  capillary  attraction  under  the  teeth  and  along  their 
pins,  and  when  the  whole  has  cooled  it  sets  hard  and  the  teeth  are  im- 
movable. The  excess  of  sulphur  may  be  removed  with  a  fine-pointed 
knife ;  the  plate  is  then  ready  for  the  final  polishing. 

This  description  of  the  method  of  fitting  tube  teeth  applies  in  every 
particular  to  all  cases,  whether  they  be  partial  or  full,  upper  or  lower. 
Different  methods  of  setting  tube  teeth  are  doubtless  practised  by  dif- 
ferent workmen,  but  it  is  believed  that  the  modus  operandi  herein 
described  is  as  simple  and  effective  as  any. 

Besides  the  ordinary  tube  teeth,  single  gum  teeth  of  this  kind  are  to 
be  had,  and  they  prove  as  satisfactory,  Avhen  judiciously  used,  as  teeth 
with  flat  backs.  Perhaps  it  may  not  be  -out  of  place  to  indicate  here 
the  style  of  case  which  will  prove  most  suitable  to  the  use  of  tubes. 
Mouths  where  all  the  masticators  have  been  lost  and  the  front  teeth 
alone  remain  are  very  favorable  cases  for  tube  teeth.  Again,  where 
alternate  teeth  are  missing  they  answer  admirably.  They  are,  however, 
not  well  suited  for  vulcanite  work,  because  from  the  weakness  of  the 
rubber  which  radiates  from  the  margin  of  the  plate  such  dentures  would 
be  liable  to  break  under  the  force  of  mastication.  But  if  a  gold  plate 
and  tube  teeth  be  constructed  for  such  a  case,  the  ease  with  wiiich  it 
can  be  repaired  is  greatly  in  favor  of  its  selection  ;  and  should  the  inter- 
mediate natural  teeth  be  lost  in  course  of  time,  other  tube  teeth  can 
-easily  be  added  to  the  old  plate  to  replace  them. 


436 


ENGLISH  TUBE  TEETH,   ETC. 


English  Tube   Crowns. 

In  this  country  during  recent  years  attention  has  occasionally  been 
called  to  English  tube  teeth  in  crown-work,  although  no  details  of  their 
application  have  been  given.  This  branch  of  practice,  however,  is  com- 
mon enough  in  England,  although  the  usual  method  of  fitting  the  tooth 
to  a  model,  fixing  pin  and  tooth  together,  and  finally  cementing  them 
upon  the  root,  is  open  to  many  objections — among  others,  loss  of  time 
incurred  in  taking  the  model  and  bite  and  want  of  accuracy  in  fitting. 

An  improvement  in  setting  tube  crowns  has  been  made  by  Mr.  John 
Stewart,  L.  D.  S.,  of  Edinburgh.     The  method  is  as  follows  :  The  root 

Fig.  513. 


Single  root  pin,  with  post 
for  tube  crown. 


Bifid  root  pins,  with  posts 
for  tube  crowns. 


is  prepared  in  the  usual  manner.  If  part  of  it  remain  above  the  level 
of  the  gum,  the  rubber  dam  is  applied  to  one  tooth  on  each  side  before 
excising,  having  first  ansesthetized  the  gum  by  painting  on  a  20  per  cent, 
solution  of  cocaine.  A  ligature  is  used  in  preference  to  a  clamp  for  fixing 
the  rubber,  because  the  latter  interferes  with  the  bite  when  the  pin  comes 
to  be  adjusted.  The  rubber  dam  is  pushed  up  as  far  as  possible  on  the 
lingual  and  labial  or  buccal  aspect  of  the  root,  for  the  reason  that  thi& 
kind  of  crown,  being  bandless,  requires  to  have  its  weak  point,  the  union 
of  root  and  crown,  covered  by  the  gum  when  the  dam  is  taken  off.  The 
canal  is  then  enlarged  with  a  twist  drill  a  size  larger  than  the  diameter 
of  the  wire  to  be  used  as  a  post.  If,  as  often  happens  in  the  first  bicus- 
pid, the  canal  be  bifid,  a  piece  of  wire  may  be  bent,  as  in  Fig.  513,  ta 
fit  into  each  canal,  and  to  it  the  straight  post  should  be  soldered  ;  or  the 
straight  pin  may  be  "kneed,"  as  in  Fig.  514,  and  an  additional  "leg'' 
soldered  to  it.  Both  ways  are  practicable,  provided  the  soldering  be  done 
securely.  The  post  may  be  made  of  gold,  platinum,  or  English  dental 
alloy.  The  post,  where  possible,  should  have  a  fine  shallow  thread  cut 
on  it,  except  where  it  emerges  from  the  root  to  enter  the  crown.  This 
part  is  the  weakest,  and  its  strength  should  not  be  impaired  even  by 
a  screw-thread. 

Having  selected  a  suitable  tooth,  it  is  fitted  roughly  to  the  root  before 
applying  the  rubber  dam.  On  ascertaining  that  it  fits  fairly  well,  the 
pin  is  placed  in  the  root  and  tried  on  the  crown  :  if  it  be  much  out  of 
line  with  the  other  teeth,  its  position  must  be  corrected,  either  by  bend- 
ing the  pin  at  the  junction  of  root  and  crown,  or  by  reaming  the  canal 
in  the  direction  necessary,  or  by  a  combination  of  both  operations.  The 
tooth  and  the  pin  are  then  triecl  on  once  more :  if  everything  is  right,  the 
walls  of  the  canal  are  grooved  with  a  wheel  burr ;  mix  the  cement,  and, 
placing  a  little  oxyphosphate  cement  in  the  canal  and  around  the  pin, 
the  latter  is  forced  to  its  place  with  the  pliers  (Fig.  504).     While  the 


ENGLISH  TUBE  CROWNS.  437 

cement  is  still  soft  the  base  of  the  crown  is  slightly  oiled  and  slipped  on 
to  the  pin  to  ensure  its  correct  position  before  the  cement  sets.  It 
should  be  held  in  place  until  the  cement  sets.  Then,  having  taken  oif 
the  crown,  the  surplus  cement  is  to  be  trimmed  from  the  end  of  the  root. 
This  part  of  the  root  may,  if  thought  desirable,  be  cut  out  around 
the  post  and  filled  with  gold  or  amalgam.  This,  however,  is  not 
necessary  except  in  cases  where  the  root  has  been  much  weakened  by 
decay. 

The  bite  Avill  at  this  point  claim  attention.  The  patient  is  directed  to 
close  the  teeth,  and  the  post  is  ground  down  until  it  ceases  to  interfere 
with  complete  closure.  When  no  clamp  is  used,  the  rubber  dam  will 
not  interfere  to  any  extent  with  this  part  of  the  work.  The  tooth  is 
now  fitted  to  the  root,  as  would  be  done  on  a  plate,  but  instead  of  using 
vermilion  paint  for  fine  fitting,  a  small  disk  of  the  thinnest  articulating 
paper,  in  the  centre  of  which  a  hole  must  be  made  with  the  rubber-dam 
punch,  is  slipped  over  the  pin  to  the  face  of  the  root.  The  tooth  is 
then  pressed  to  place  and  ground  oflP  where  it  is  marked  until  a  perfect 
fit  is  obtained.  The  articulation  is  then  carefully  adjusted.  The  cervi- 
cal margin  is  examined,  and  if  the  crown  overlap  the  root,  the  excess  of 
porcelain  is  to  be  removed  until  the  sides  of  root  and  crown  are  continu- 
ous. Previous  to  setting,  the  base  of  the  crown  should  be  hollowed  out, 
care  being  taken  to  avoid  the  edges  :  this  provides  for  the  presence  of  a 
body  of  cement  between  the  root  and  the  crown,  as  in  the  Logan  and 
other  crowns.  The  tube  is  to  be  thoroughly  cleaned  out  and  roughened 
in  its  interior,  as  in  plate-work,  and  fastened  to  the  pin  and  root  with 
cement,  pressing  it  firmly  to  place  with  a  Bonwill  crown-setter.  The 
head  of  the  pin  may  be  riveted  with  an  engine-burnisher,  and  the  bite 
should  be  examined  before  the  patient  leaves. 

The  shaping  of  the  root  is  a  matter  of  choice.  The  two  which  have 
found  most  favor  are  the  well-known  '-new  Richmond"  (Fig.  515)  and 

Fig.  515.  Fig.  516. 


New  Richmond.  Ordinary  saddle-shaped. 


the  "saddle"  (Fig.  516)  shapes.     The  crown  to  suit  the  former  may  be 
fitted  by  hand  with  a  three-sided  corundum  file. 

Many  suggestions  have  been  made  regarding  the  posts  and  pins  : 
some  operators  prefer  that  they  be  made  of  square  or  oval  forms  of  wire, 
in  order  to  prevent  rotation  ;  but  if  the  roots  have  been  properly  pre- 
pared, rotation  cannot  possibly  take  place  unless  the  crown  first  becomes 
loose — an  accident  which  in  practice  rarely  occurs.  Besides  being  un- 
necessary, square  or  oval  pins  are  a  positive  drawback,  and  they  greatly 
limit  the  usefulness  of  this  form  of  crowns.  They  demand,  in  the  first 
place,  an  unnecessary  enlarging  of  the  canal,  and  consequently  weaken 
the  root,  and  as  posts  they  possess  less  strength  than  do  round  ones ; 
and  it  is  sometimes  found  that  after  the  pin  has  been  set  the  direction 


438  ENGLISH  TUBE  TEETH,   ETC. 

of  the  crown  is  not  all  that  could  be  desired,  or  that  either  the  mesial  or 
distal  corner  stands  a  little  out  of  line.  Where  a  square  or  oval  post 
has  been  used  this  cannot  be  corrected,  except  by  the  removal  and  read- 
justment of  the  post ;  whereas  when  it  is  round  the  crown  can  be  turned 
on  its  axis  in  any  direction  required  at  any  stage  of  the  fitting.  For 
these  reasons  round  posts  are  generally  superior  in  this  class  of  work  to 
all  other  forms. 


Tube  Crowns  on  Metallic  Caps. 

If,  for  any  reason,  it  is  considered  advantageous  to  protect  the  sur- 
face of  the  root  by  means  of  a  metallic  cap  and  band,  the  rubber  dam 
must  be  dispensed  with.  The  root  is  trimmed,  the  sides  made  parallel, 
and  after  fitting  a  collar  to  it,  leaving  the  gold  a  trifle  high,  the  canal  is 
prepared  and  a  post  loosely  inserted  into  it.  A  plaster  impression  and 
bite  of  the  whole  is  then  taken.  The  pin  and  band  will  generally  come 
away  with  the  impression,  or,  should  they  not  do  so,  they  can  be  easily 
removed  from  the  root  and  replaced  in  the  plaster.  After  running  the 
model,  a  coin-gold  cap.  No.  30  thickness,  is  fitted  and  soldered  to  the 
band  :  through  it  a  hole  is  drilled  for  the  pin  ;  it  is  then  placed  on  the 

Fig.  517.  Fig.  518. 


Elevation  showing  blackened  bicuspid.  Fiepared  root. 

model,  the  pin  is  inserted  and  its  direction  corrected  by  bending  before 
soldering  to  the  cap.  The  pin  may  be  easily  bent  if  nicked  with  a  file, 
and,  as  any  weakness  caused  thereby  is  repaired  by  the  soldering,  it  in 
no  way  imperils  the  soundness  of  the  post.  Having  boiled  in  pickle, 
the  assembled  pin,  cap,  and  band  are  returned  to  the  plaster  model,  and 
the  crown  is  fitted  as  previously  described.  This  done,  it  is  cemented  to 
cap  and  pin  before  inserting  them  in  the  mouth.  This  makes  a  strong 
and  beautiful  crown,  and,  while  it  is  especially  applicable  to  single-rooted 
teeth,  it  may  also  be  occasionally  employed  on  some  molar  roots. 

Tube  Crowns  on  Living  Teeth. 

It  is  seldom  that  tube  teeth  can  be  used  for  this  purpose,  but  Dr. 
Girdwood  reports  two  cases  which  he  treated  with  gratifying  success. 
Fig.  517  is  the  first  of  these,  and  represents  a  lower  left  first  bicuspid, 
which  had  a  large  amalgam  filling,  extending  to  the  crown,  on  each 
of  its  proximal  surfaces.  The  tooth  was  much  discolored,  and  by 
its  presence  the  appearance  of  an  otherwise  good  set  of  teeth  was 
spoiled.  The  patient  objected  to  the  extirpation  of  the  pulp.  The 
bite  was  close,  yet  the  teeth  showed  considerably.  An  all-gold  crown 
would   have  been  too   conspicuous,  a  porcelain-faced  one  worthlessly 


ENGLISH  TUBE  TEETH  IN  BRIDGE-WORK. 


439 


Fin. 


'^^^-^2:^^'^^ 


weak.     Therefore,  it  was  decided  to  grind  down  the  buccal  aspect  of  the 

root  nearly  to  the  gum  margin   (Fig.    518),   leaving  the   lingual    side 

considerably  higher.     A  cap  and  band 

were    made    to    fit    the     root     tightly 

and    to    pass    a    short    distance    under 

the   gum  :   a    pin  was  soldered    to  this 

and  a  tube    tooth  adjusted   to    it    and 

the  bite,  and  the  whole  cemented  (Fig. 

519)  on  the  living   root.     The  buccal 

side  of  the  22-carat  gold  band  is  almost 

covered  by  the  gum,  and  what  is  seen  of 

it  looks  like  a  small  cervical  filling.    The 

second  case  reported  by  Dr.  Girdwood 

does  not  differ  essentially  from  the  first, 

except  that  the  bite  is  somewhat  closer 

and  the  crown,  if  anything,  more  severely  tested. 


Elevation  showing  bicuspid  tooth. 


English  Tube  Teeth  in  Bridge-work. 

As  is  well  known,  one  of  the  greatest  objections  to  ordinary  bridge- 
work  consists  in  the  difficulty  met  with  in  concealing  the  gold  so  as  not 
to  be  seen  when  the  patient  talks  or  laughs.  By  the  use  of  English  tube 
teeth  it  is  claimed  that  this  objection  may  be  entirely  obviated. 


Fig.  520. 


Model  for  removable  bridge. 

For  fixed  bridges  replacing  the  front  teeth  tube  teeth  are  less  suitable, 
because  of  the  difficulty  encountered  in  securing  proper  self-cleansing 
spaces,  the  sine  qua  non  of  the  perfect  bridge. 

The  case  shown  in  Fig.  520,  where  the  cuspids  are  past  filling  and 
the  molars  still  stand,  will  serve  to  explain  the  manner  of  constructing 
a  large  removable  plate  bridge  with  tube  teeth.  The  crowns  of  the  cus- 
pids are  to  be  cut  level  with  the  gum,  and  the  roots  prepared  after  the 
usual  fashion :   the  canals  are  to  be  drilled  to  receive  a  gold  or  platinum 


440 


ENGLISH  TUBE  TEETH,   ETC. 


tube,  which  should  be  as  long  as  possible  and  sufficiently  wide  to  accom- 
modate a  No.  13  post  of  hard  gold.  The  molars  are  next  trimmed  to 
receive  gold  crowns,  and  a  considerable  notch  is  cut  in  the  crown  and 
anterior  proximal  surface  of  each.  This  notch  (the  object  of  which  will 
be  presently  explained)  should  not  extend  on  the  coronal  surface  more 
than  halfway  back,  nor  on  the  anterior  aspect  more  than  halfway  from 
the  crown  to  the  gum.  Tubes  are  then  placed  in  the  roots  of  the  cuspids 
and  allowed  to  project  about  three-eighths  of  an  inch.  An  impression 
of  the  mouth  is  next  taken  in  plaster,  in  which  the  tubes  will  come 
away,  and  it  is  run  out  and  opened  as  usual.  The  plaster  teeth  and 
roots  are  now  trimmed,  so  that  the  cuspid  caps  and  molar  crowns  when 
made  will  pass  a  little  way  beneath  the  gum  margin.  The  pattern  of 
cap  and  band  for  the  cuspid  is  the  "  Richmond,"  and  care  should  be 
taken  that  each  is  made  level  with  the  gum  on  the  labial  side  (Fig.  521). 
Hard  gold  or  platinum  tubes  are  next  soldered  to  them  in  lieu  of  the 
ordinary  posts  of  single  "  Richmond  "  crowns.  The  fixing  of  these  with 
cement  in  their  proper  positions,  and  the  operation  of  sealing  the  apical 


Fig.  521. 


Fig.  522. 


Cap,  Vjaud,  and  tube  soldered. 


t^tiuck  crown  for  molar. 


ends  with  gold  or  amalgam,  complete  the  preparation  of  the  roots.  They 
are  then  ready  to  receive  their  posts  (Fig.  5:^1).  A  "  Mellotte '_'  die  of 
each  molar  is  then  taken  and  a  gold  collar  made  to  fit  it.  This  collar 
is  notched  on  its  anterior  surface  (Fig.  523)  to  suit  the  corresponding  de- 
pression on  the  same  surface  of  the  natural  tooth  ;  the  band  is  put  on  the 


Fig.  523. 


Fig.  524. 


Band  for  molar. 


Pure  gold  cap. 


"Mellotte"  cast  and  a  piece  of  No.  30  pure  gold  (Fig.  524)  is  placed 
over  the  crown  and  burnished  to  fit  its  upper  surface  and  the  floor  of 
the  notch  referred  to.  When  this  is  soldered  to  the  collar  it  gives  an 
all-gold  crown  without  cusps.  A  pure-gold  cap  is  next  struck  up  and 
filled  in  with  coin  gold :  it  is  ground  level  on  its  under  surface,  and  is 
in  turn  notched  at  the  same  part  as  the  gold  crown  already  made. 
Having  adjusted  it  to  the  latter,  they  are  soldered  together,  and  an 
ordinary  all-gold  crown  is  the  result,  plus  the  recess  on  the  crown 
and  anterior  surface  (Figs.  522  and  526). 

These  crowns  are  cemented  upon  their  respective  teeth.     Posts  with 
bent  ends  are  now  placed  in  the  cuspid  tubes  and  allowed  to  project  from 


ENGLISH  TUBE  TEETH  IN  BBIDGE-WOBK. 


441 


them  about  three-eighths  of  an  inch  or  more.  A  plaster  impression  of 
the  whole  is  now  to  be  taken,  and  the  pins  will  come  away  in  it  if  the 
direction  of  the  cuspid  tubes  has  been  carefully  considered.  Before 
casting  the  imjDression  a  small  piece  of  metal  tubing  of  such  a  size  as  will 
exactly  fit  the  posts  is  slipped  over  each  :  this  will  prevent  any  alteration 
in  their  direction  when  they  have  to  be  withdrawn  and  replaced  in  their 
sockets  during  the  making  of  the  bridge. 

Having  cast,  opened,  and  hardened  the  model,  the  next  procedure  is 
to  make  the  clasps  for  the  fixed  molar  crowns,  as  follows  :  First,  take  a 
^'  Mellotte "  die  of  each  tooth  and  cut  a  pattern  as  in  Fig.  525,  being 
careful  to  leave  a  portion  of  it  (i?)  high  enough  above  the  level  of  the 
tooth  to  permit  of  its  being  bent  down  and  accurately  fitted  into  the 
notch.  The  clasp  is  next  fitted  to  the  tooth,  and  the  portion  (B)  is 
thinned  down  with  a  file  and  punched  till  it  fits  into  the  depression  as 


Fig.  525. 


Fig.  526. 


Portion  of  band  pattern. 


Molar  crown,  notched  and  completed. 


just  indicated.  It  is  now  strengthened  and  contoured  to  the  normal 
shape  of  the  crown  by  the  addition  of  pieces  of  hard  gold  soldered  to- 
gether with  21 -carat  solder.  This  forms  a  strong  partial  cap  or  spur, 
which,  bearing  on  the  gold  crown,  prevents  the  bridge  settling  too  hard 
upon  the  gum.  It  is  better  to  make  the  band  and  spur  from  one  piece 
of  metal,  as  shown  in  Fig.  525,  than  to  solder  the  spur  to  the  band  when 
fitted,  for  by  the  former  way  the  continuity  of  the  metal  is  unbroken. 


Plan  showing  bridge-plate 


The  clasp  must  be  prolonged  posteriorly  to  grasp  the  distal  surface  of 
the  crown,  in  order  that  any  tendency  on  the  part  of  the  tooth  to  back- 
ward movement  by  pressure  on  the  spur — which  will  thus  act  as  an  in- 
clined plane — may  be  prevented  (Fig.  527). 


442  ENGLISH  TUBE  TEETH,   ETC. 

The  next  step  is  the  swaging  of  the  plate,  which  is  made  of  two  thick- 
nesses of  metal,  the  first  being  made  of  No.  24  gauge  ^  and  about  five- 
eighths  of  an  inch  wide  all  round.  It  must  be  stuck  up  sharply  and 
made  to  cover  the  cuspid  caps.  Next  a  piece  of  plate.  No.  26  gauge,  and 
a  trifle  narrower  than  the  first,  is  swaged  over  the  latter.  When  fitted 
the  two  are  soldered  together  with  21-carat  gold  solder.  The  thick 
single  plate  thus  produced  is  trimmed  to  the  shape  shown  in  Fig.  456. 
After  having  seen  that  the  plate  fits,  it  is  drilled  through  opposite  each 
cuspid  tube  to  receive  the  posts,  which  are  introduced  into  the  tubes  and 
allowed  to  project  through  the  drill  holes  on  the  lingual  surface.  The 
clasps  are  then  adjusted,  and  a  little  plaster  placed  around  them  and  the 
cuspid  posts.  When  it  is  hardened  the  various  parts  are  removed  from 
the  model  and  fixed  in  their  respective  places  :  they  are  then  invested 
and  soldered  with  20-carat  solder. 

If  the  cuspid  tube-tooth  posts  be  thicker  than  the  size  of  pin  wire, 
they  are  to  be  reduced  by  the  file  to  suit  the  porcelain  teeth. 

The  teeth  are  now  adjusted  as  described  in  their  plate  application,  the 
finished  piece  is  shown  in  Fig.  528. 

Modification  of  this  method  can  be  used  in  the  construction  of  any 
removable  tube-tooth  bridge.  The  point  to  be  especially  noted  is  the 
treatment  of  the  molars,  a  plan  which  can  be  adapted  to  suit  any  of  the 

Fig.  528. 


Side  view  of  teeth  on  bridge-plate. 

posterior  teeth.     It  most  surely  prevents  the  "  settling  "  of  the  denture 
and  the  tendency  to  movement  on  the  part  of  the  natural  teeth. 

Fixed  Bridge-work. 
Fixed  bridge-work  offers  but  a  limited  scope  to  English  tube  teeth, 
for  they  can,  as  a  rule,  be  used  as  substitutes  for  the  masticating  teeth 
only,  or,  at  most,  behind  the  laterals.  As  already  mentioned,  the  obstacle 
to  their  utilization  in  restoring  the  front  teeth  is  the  much-discussed  self- 
cleansing  space,  which  cannot  readily  be  gotten  by  any  all-porcelain 
crowns,  for  reasons  which  render  useless  the  adaptation  of  Logan,  Bon- 
will,  and  other  crowns  to  like  purposes.  The  idea  must  not  be  formed, 
however,  that  the  tube  teeth  can  never  be  used  here ;  but,  on  account  of 
the  shape  of  a  front  tooth  which  necessitates  a  short  and  weak  lingual 
surface,  often  to  be  further  destroyed  to  accommodate  the  bite,  it  is  in- 
advisable to  use  them  except  in  the  few  cases  where  the  bite  of  the  lower 

^  English  gauge. 


FIXED  BRIDGE-WORK. 


44;^ 


teeth  strikes  abnormally  far  in.  Here  they  may  safely  be  applied.  Fig. 
529  represents  the  kind  of  case  in  which  a  fixed  bridge  with  English  tube 
teeth  answers  admirably.     The  gap  in  the  dental  arch  extends  from  the 


Fig.   529. 


Mould  for  fixed  bridge. 


third  molar  to  the  first  bicuspid.  The  first  bicuspid  is  banded  and  capped^ 
and  a  pin  which  acts  as  a  post  both  to  the  root  and  tube  crown  is  soldered 
through  it  (Fig.  530).     A  gold  crown  is  fitted  to  the  third  molar,  and  a 


Fig.  530. 


Posts  trimmed. 

strong  ovai-shaped  22-carat  gold  bar,  which  will  connect  the  crown  and  cap, 
and  ultimately  carry  the  teeth,  is  made.  This  bar  ought  not  to  rest  on  the 
alveolar  ridge,  but  must  be  about  one-sixteenth  of  an  inch  from  it,  and 
its  angle  with  the  alveolar  border  ought 
to  be  as  represented  in  the  section  shown 
(Fig.  532,  A-B).  Such  a  slope  down- 
ward from  the  lingual  to  the  labial 
side  will  secure  a  perfect  self-cleans- 
ing space.  The  anterior  end  of  the 
bar  must  now  be  soldered,  not  only  to 
the  bicuspid  cap,  but  to  the  base  of 
the  post  itself,  so  that  the  strain  may  be 
borne  by  both  (Fig.  531).  So  far,  then, 
the  bar  and  bicuspid  cap  are  in  one 
piece,  the  molar  crown  remaining  un- 
attached. These  are  to  be  placed  in 
their  relative  position  in  the  mouth, 
and  any  adjusting  made  that  may  be 
necessary  between  the  molar  crown  and  the  posterior  end  of  the  bar  : 
they  are  then  taken  off  with  plaster,  as  described  in  this  operation  in 


Bridge  with  teeth  ready  for  fixing. 


444 


ENGLISH  TUBE  TEETH,   ETC. 


Fig.  532. 


plate  bridge,  and  soldered.  A  bite  must  then  be  taken,  and  the  teeth 
set  up  on  the  bar  in  the  usual  way,  being  fitted  to  it  and  allowed  to  over- 
hang its  buccal  edge,  as  represented  in  the  section  (Fig.  532).  When 
the  teeth  have  been  cemented  to  place  with  sulphur,  the  bridge  should 
be  fixed  temporarily  in  the  mouth  until  it  has  proved  satisfactory,  when 
it  may  be  permanently  fastened.  A  fixed  bridge  like  this  may  be  in- 
serted on  either  side  of  either  jaw,  and  modified  to  suit  such  exigencies 
as  intermediate  roots,  etc. 

It  must  not  be  concluded  that  the  possibilities  of  tube-work  have  by 
any  means  been  exhausted  in  the  descriptions  herein  given.  Their  uses 
seem  to  be  limited  by  faults  in  construction  of  the  front  teeth,  previously 
mentioned,  and  shown  in  Fig.  498,  A.  A  porcelain  crown  has  lately  been 
made  which  is  almost  identical  with  the  tube  tooth  herein 
described  (Fig.  533).  Speaking  of  this  special  crown,  Dr. 
John  Gird  wood  says :  "It  is  made  to  replace  front  teeth 
and  bicuspids.  The  bicuspids  are  well  designed  but  as 
much  cannot  be  said  for  the  fronts,  for,  although  the  posi- 
tion of  the  tube  has  been  corrected,  the  crown  is  still  com- 
paratively worthless,  on  account  of  its  needlessly  weak 
lingual  wall,  further  undermined  in  many  cases  by  a  too 
much  countersunk  base.  Because  of  these,  to  me,  very 
serious  defects,  I  have  never  used  the  new  crowns,  so  I  do 
not  on  this  point  speak  from  experience.  Despite  their  in- 
troduction, an  improved  tube  tooth  is  called  for." 

A  point  of  great  moment  to  the  tube-worker  is  the  alloys 
of  gold  for  posts.  In  plate-work  these  are  made  by  Eng- 
lish dentists  about  18  carats  fine.  This  comparatively  poor 
grade  of  metal  is  good  enough  for  plate-work,  but  in  crown-  and  bridge- 
work  something  finer  is  required.  The  qualities  most  to  be  desired  are 
toughness  and  non-liability  to  tarnish,  and  these  can  be  secured  by 
alloying  coin  gold  with  from  1|  to  2  pennyweights  of  platinum  to  the 
ounce  :  this  makes  an  excellent  alloy  for  all  pins,  posts,  plates,  and  bars. 
It  is  so  infusible  that  it  may  safely  be  soldered  with  coin  gold  22  carats 
fine. 

The  use  of  sulphur  as  an  agent  for  fixing  teeth  on  plates  and  bridges 
has  long  been  practised  by  English  dentists,  and  the  question  of  prefer- 
ence between  it  and  the  oxyphosphate  cements  has  been  widely  discussed 
by  them.     Its  advocates  claim  that,  except  in  crowns  and  other  situations 

where  it  cannot,  from  its  very  nature, 
be  employed,  sulphur  is  much  the  bet- 
ter of  the  two  materials ;  which  will 
stand  in  mouths  where  from  the  cha- 
racter of  the  oral  secretion  the  cements 
undergo  rapid  solution,  and  that  none 
of  the  oral  fluids  destroy  sulphur.  It 
certainly  has  the  advantage  when  re- 
pairs have  to  be  done.  Where  cement 
has  been  the  fixing  medium  the  teeth  can  only  be  removed  with  great 
force — obviously  a  very  unsafe  proceeding.  Indeed,  if  the  pin  and  tube 
have  been  well  roughened,  the  teeth  cannot  be,  in  many  cases,  gotten  oif 
without    fracturing    them.     By  the  use  of   sulphur,  however,  all    this 


Fig.  533. 


Side. 
Ash's  new  tube  crowns. 


FIXED  BRIDGE-WORK.  445 

trouble  is  prevented,  for  when  the  plate  comes  to  be  repaired  it  has  only 
to  be  heated  carefidly  and  gradually  until  the  sulphur  melts,  when  the 
teeth  may  be  easily  lifted  from  their  pins  and  refixed  when  the  repair  is 
effected. 

Objection  is  sometimes  made  to  the  appearance  of  the  pins  on  the 
coronal  surface  of  tube  teeth.  This  objection  may  be  overcome  by  cutting 
as  much  off  the  pin  as  is  thought  necessary,  without  impairing  its  func- 
tion as  a  support  to  the  tooth;  then  cut  a  piece  from  a  white  glass  or 
porcelain  rod  of  proper  size  in  the  tube  over  the  pin.  This  ought  to  be 
done  before  the  teeth  are  finally  fixed,  so  that  the  section  of  glass  or 
porcelain  will  be  firmly  held  by  the  sulphur.  When  finished  the  most 
critical  observer  will  hardly  detect  any  break  in  the  color  of  the  crowns 
if  the  inlays  have  been  well  matched. 


CHAPTER    XIII. 

CONTINUOUS-GUM  DENTURES. 

By  Ambler  Tees,  D.  D.  S. 


The  variety  of  artificial  denture  known  as  continuous  gum  consists 
of  a  base-plate  of  platinum,  to  which  plain  teeth  are  first  attached  by 
means  of  solder,  the  contours  of  the  natural  gum  and  palatal  vault  being 
formed  of  a  porcelain  body  fusing  at  a  lower  temperature  than  the  com- 
ponents of  the  artificial  teeth,  over  which  an  enamel  closely  resembling 
the  gum  color  is  subsequently  fused. 

Our  present  conceptions  of  the  work  and  the  methods  of  its  con- 
struction are  due  to  the  late  Dr.  John  Allen  of  New  York.  The  prin- 
ciples involved  have  their  authorship  traceable  to  the  dental  fraternity  in 
France,  although  their  experiments  and  methods  were  crude  compared 
with  those  of  Dr.  Allen. 

In  1815,  M.  de  Chemant  obtained  a  patent  for  the  manufacture  of 
porcelain  or  "  incorruptible  mineral  teeth."  The  denture  was  constructed 
in  one  piece ;  the  coloring,  to  imitate  the  natural  gum,  was  applied  by 
means  of  brushes  subsequent  to  the  vitrification  of  the  piece.  The  pig- 
ments employed  were  destructible  by  the  secretions  and  fluids  of  the 
mouth. 

In  1818,  MM.  de  Fouze  and  Delabarre  applied  jeweller's  enamel  to 
the  purposes  of  gum  restoration  :  this  was  found  to  crack  and  flake  from 
the  plate.  M.  Delabarre  then  conceived  the  plan  of  using  individual 
teeth  and  surrounding  them  by  a  porcelain  the  fusing-point  of  which 
was  lower  than  that  of  the  teeth.  His  experiments  were  partially  suc- 
cessful, but  attracted  scant  attention,  and  the  manufacture  of  continuous- 
gum  dentures  languished  until  1846,  when  Dr.  Allen  compounded  a 
porcelain  body,  now  in  use,  for  which  he  obtained  a  patent  in  1851. 
We  are  indebted  to  him  not  alone  for  the  formulae  themselves,  but  for 
methods  of  design  and  construction.  He  first  demonstrated  the  feasi- 
bility of  restoring  lost  facial  contour. 

In  comparing  the  several  features  of  this  variety  of  artificial  dentures 
with  those  constructed  upon  other  bases,  what  have  been  deemed  supe- 
rior virtues  have  been  claimed  for  it,  and  certain  disadvantages  arrayed 
against  it. 

It  is  the  most  cleanly  of  all  artificial  dentures ;  its  plate-base,  com- 
posed of  pure  platinum,  is  entirely  uninfluenced  by  ordinary  chemical 
agencies.  There  are  no  interstices  in  which  food  debris  or  secretions 
may  find  lodgement  and  become  offensive  through  subsequent  decompo- 
sition. Worn  for  a  score  of  years,  the  piece  when  scrubbed  is  practically 
as  clean  as  when  it  came  from  the  furnace. 

Any  configuration  may  be  given  the  porcelain  body,  so  that  the  ope- 
rator may  at  will  restore*  to  a  degree  limited  only  by  his  taste  and  skill 

446 


CONTINUOUS-GUM  DENTURES.  Ml 

any  loss  of  gum  or  palatal  contour.  When  the  palatal  aspect  of  the 
piece  is  exposed,  its  artificiality  is  not  noted,  as  with  dentures  constructed 
upon  other  bases. 

The  objections  urged  against  it  are,  first,  its  great  weight  as  com- 
pared with  other  artificial  dentures.  This  objection  is  found  to  be  more 
apparent  than  real,  for  a  patient  rarely  complains  of  the  weight  of  a 
properly  adapted  continuous-gum  denture. 

Second,  it  is  asserted  that  the  inevitable  contraction  of  the  porcelain 
body  causes  more  or  less  change  of  form  of  the  platinum  base-plate. 
Faults  in  this  direction  are  largely  traceable  to  lack  of  skill  upon  the 
part  of  the  operator :  with  increased  familiarity  with  this  class  of  work 
difficulties  in  the  direction  named  diminish. 

The  next  objection  is  the  liability  to  fracture  :  certainly  increased 
care  upon  the  part  of  the  wearer  is  necessary  to  avert  accidents  with  a 
porcelain  piece.  Fracture  occurs  usually  while  the  patient  is  washing 
the  piece  :  if  the  precaution  is  taken  to  place  a  folded  towel  in  the  bot- 
tom of  a  basin  of  water  and  wash  the  denture  while  held  over  the  basin, 
or  to  use  a  paper  basin,  it  may  drop  then  without  fracturing.  Breakage 
while  in  actual  use  very  rarely  occurs.  In  95  per  cent,  of  cases  of  repair 
the  cause  of  breakage  is  that  first  noted,  carelessness  in  handling  by  the 
patient.  The  writer  has  seen  continuous-gum  dentures  after  twenty-five 
years  of  use  as  perfect  and  beautiful  as  the  day  they  were  inserted. 

One  reason  adduced  for  their  limited  employment  has  been,  the  annoy- 
ance and  difficulty  in  the  operations  of  attaching  the  porcelain  and 
enamel.  These  objections  are  now  largely  removed  through  the  im- 
proved forms  of  furnaces  employed  :  with  these  the  work  will  be  found  a 
pleasure.  They  also  remove  another  heretofore  objection — the  difficulty 
and  expense  of  repairing  a  denture  in  case  of  fracture.  The  electric  oven 
of  Dr.  Custer  makes  the  operation  of  repairing  continuous  gum  a  mere  trifle. 

When  upper  and  lower  dentures  of  continuous  gum  are  worn,  it  is 
common  to  find  the  teeth  produce  a  clicking  sound  when  occluding. 
The  writer  has  attributed  this  to  faulty  adaptation  of  the  lower  piece. 
The  intense  heat  to  which  a  plate  is  subjected  in  fusing  the  porcelain 
body  upon  it  causes  a  change  of  form  to  the  horseshoe-shaped  piece  of 
the  lower  plate,  and  upon  the  completion  of  the  operation  the  two  plates 
are  not  uniformly  supported  by  their  cushions,  the  alveolar  arches.  This 
warpage  may  be  prevented  by  a  means  to  be  described  later.  This 
fault  is  common  to  all  full  artificial  dentures,  upon  whatever  base  they 
may  be  mounted,  if  the  same  faults  of  adaptation  obtain.  To  prevent  the 
clicking  Dr.  John  Meyer  has  suggested  that  metallic  fillings  be  placed  in 
the  articulating  faces  of  the  molars. 

The  term  "  continuous  gum  "  applies  to  all  pieces  in  which  the  arti- 
ficial gums  and  teeth  are  so  attached  as  to  form  one  piece,  no  matter  of 
what  material  the  base-plate  may  be  constructed  ;  for  example,  the  portion 
of  an  artificial  denture  composing  gums  and  teeth  may  be  made  in  an  arch 
of  porcelain,  and  this  subsequently  mounted  upon  a  plate  of  vulcanite. 

Continuous  gum  is,  as  a  rule,  employed  alone  for  full  cases,  either 
upper  or  lower.  It  is  quite  possible  to  construct  a  partial  piece  of  this 
material  when  the  teeth  to  be  replaced  are  in  a  large  and  continuous 
column.  Occasionally  pieces  have  been  made,  and  comfortably  worn, 
where  the  restoration  embraced  the  posterior  inferior  teeth  of  both  sides. 


448 


CON  TIN  UO  US-G  UM  DENTURES. 


The  Impression. 

The  physical  properties  of  plaster  of  Paris  recommend  it  above  all 
other  impression  materials,  although  some  operators  prefer  wax  or 
modelling  compound  for  taking  the  impression  of  cases  which  exhibit 
uneven  density  of  the  tissues  of  the  palatal  vault.  (See  Chapter  VIII.) 
The  model  is  made  as  for  any  case  in  which  dies  are  to  be  formed. 

The  advisability  of  a  vacuum  chamber  is  a  much-mooted  question. 
In  cases  which  exhibit  a  moderately  deep  and  symmetrical  vault  a  satis- 
factory adhesion  may  be  secured  without  the  chamber,  though  a  greater 
adhesion  is  had  where  the  chamber  is  employed  (Figs.  534  and  535). 

Fig.  534. 


Showing  form  of  arch  where  chamber  may  not  be  necessary. 

The  chamber-piece  is  formed  and  applied  as  described  in  Chapter 
IX.  The  plate  outline  is  marked  as  described  in  the  same  chapter : 
whether  for  upper  or  lower  case,  it  must  be  at  such  a  line,  free  from  im- 
pingement upon  the  movable  tissues,  as  shall  ensure  against  future 
trimming  of  the  plate  edge.  A  layer  of  wax  about  one-eighth  of  an 
inch  or  more  thick  is  built  upon  the  wall  of  the  model  as  shown  in  Fig. 
535.  It  is  carved  to  meet  the  plate  line  at  a  sharp  angle  and  as  acute 
as  may  be  consistent  with  accurate  moulding.  The  wax  should  exhibit 
a  flat  shelf-like  surface,  which  when  reproduced  in  the  die,  serves  to  form 
the  upper  rim.  Special  care  is  necessary  in  forming  the  wax  for  lower 
dentures,  as  these  plates,  owing  to  a  tendency  to  bury  in  the  gum,  are 

Fig.  535. 


Cast  of  the  upper  jaw,  with  ledge  for  turning  the  rim. 

carried  beyond  the  original  plate  outline  after  being  worn  for  a  period. 
In  addition  the  crest  of  the  ridge  in  lower  cases  should  receive  a  film  of 


FORMING   THE  PLATE.  449 

wax  to  compensate  for  any  bruising  of  the  die.  The  wax  wall  in  lower 
cases  is  made  continuous,  along  the  entire  plate  outline,  inside  and  outside. 

Across  the  posterior  plate  outline  for  upper  cases  a  wax  wall  about 
one-eighth  of  an  inch  thick  is  placed,  making  the  line  of  junction 
between  the  wax  and  model  sharp  and  distinct :  this  wax  is  to  join  that 
upon  the  alveolar  line,  uniting  as  the  lines  pass  behind  the  condyles. 
When  the  tissues  of  the  palatal  vault  at  the  site  of  the  posterior  edge 
of  the  plate  are  soft,  it  is  usual  to  terminate  the  plate  at  its  heel,  with- 
out raising  a  rim  :  the  latter  is  then  to  be  formed  as  described  later. 
The  model  is  now  varnished  preparatory  to  moulding. 

Matrices  are  prepared,  dies  and  counter-dies  made,  as  described  in 
Chapter  X.,  using  the  Hawes  flask  or  cores  where  and  when  necessary. 

Forming  the  Plate. 

The  best  specimens  of  platinum  for  continuous-gum  work  are  those 
prepared  in  France. 

Patterns  are  made  of  heavy  tin-foil  (Chapter  XL),  allowing  a  sur- 
plus, in  the  event  of  the  plate  shifting  position  slightly  in  the  die,  or  to 
more  readily  prevent  wrinkling  of  the  plate  edge.  The  pattern  is  repro- 
duced in  No.  29  platinum  for  upper  plates.  For  lower  plates  two 
laminae  of  metal  No.  29  are  employed,  one  large  enough  to  form  its 
borders  into  a  rim,  the  second,  which  is  to  be  superimposed,  extending 
to  the  angle  of  the  rim. 

In  partial  lower  cases  the  body  of  the  plate  is  to  be  of  No.  29,  and 
to  have  a  supplementary  piece  of  iridio-platinum.  No.  26,  extending 
across  the  lingual  wall  of  the  plate  behind  the  natural  teeth,  and  to 
about  one-fourth  of  an  inch  beyond  the  posterior  molars. 

The  platinum  is  well  annealed.  The  surface  of  the  die  is  covered 
with  wet  muslin,  to  prevent  contact  of  the  platinum  with  tlie  zinc,  and 
the  annealed  plate  pressed  against  the  surface  of  the  die  by  the  pressure 
of  the  ball  of  the  thumb.  The  plate  annealed,  the  pressure  is  resumed. 
The  adaptation  is  now  improved  by  means  of  the  horn  mallet,  reanneal- 
ing  the  plate  as  soon  as  it  becomes  obdurate. 

If  the  operator  prefers,  he  may  now  employ  a  partial  counter-die  to 
secure  primary  adaptation  of  the  plate  to  the  vault.  The  precaution 
should  always  be  observed  of  interposing  between  the  surfaces  of  the 
plate  and  those  of  the  die  or  counter-die  a  layer  of  thin  wet  paper  or 
muslin.  Without  this  medium  small  particles  of  zinc  or  lead  may 
attach  themselves  to  the  surface  of  the  platinum,  and  when  the  latter  is 
heated  the  base  metal  forms  an  alloy  with  the  portion  of  the  plate  upon 
which  it  rests.  These  alloys  are  very  fusible  and  contaminate  the  sur- 
face, or  they  may  perforate  the  plate.  Indeed,  it  is  well  to  drop  the 
platinum  in  hot  nitric  acid  as  soon  as  it  is  removed  from  contact  with 
the  die  or  counter-die. 

The  partial  counter-die  set  in  position,  and  tapped  until  the  vault  por- 
tions of  the  plate  are  in  apposition  with  the  die.  Removed  from  the  die, 
the  plate  is  reannealed  ;  the  same  care  exercised  to  prevent  contact  of  the 
platinum  with  the  base  metals  ;  and  the  horn  mallet  is  employed  to  adapt 
the  plate  over  the  alveolar  walls.  Should  wrinkles  develop,  at  the  incip- 
iency  of  their  formation  the  plate  is  reannealed,  and  they  are  removed  by 

29 


450  CONTINUOUS-GUM  DENTURES. 

means  of  the  mallet.  When  the  adaptation  is  fairly  accurate  the  plate  is 
set  in  the  counter-die,  beneath  and  over  it  a  layer  of  wet  muslin  :  the 
die  is  placed  in  position  and  the  plate  is  swaged.  It  is  reannealed  and 
reswaged  until  the  adaptation  to  the  die  is  complete.  The  surplus  plate 
is  cut  away  by  means  of  shears  and  files.  Should  the  plate  crack  or 
split  at  any  point,  a  piece  of  thin  platinum  is  laid  over  the  break  and 
soldered  to  the  plate  by  means  of  pure  gold.  This  is  the  solder  always 
employed  with  platinum  for  continuous-gum  work.  Alloys  of  gold,  as 
the  ordinary  solders,  containing  base  metals,  exercise  a  deleterious  influ- 
ence upon  the  coloring  matter  of  continuous  gum.  The  imion  of  plati- 
num through  the  medium  of  pure  gold  as  solder  is  much  stronger  than 
were  alloys  of  gold  employed. 

Vacuum  chambers  in  platinum  base-plates  are  formed  in  the  plate 
itself,  not  soldered  to  it,  as  with  gold  plates.  The  great  heat  of  the  fur- 
nace, required  to  fuse  the  porcelain,  causes  wide  diffusion  of  even  pure 
gold  through  the  platinum,  so  that  the  minimum  of  solder  is  to  be 
applied  in  this  work. 

If  a  second  die  has  been  made,  the  plate  is  now  transferred  to  it — 
always  a  layer  of  wet  tissue-paper  interposed,  another  layer  over  the 
plate — the  counter-die  set  in  position,  and  the  swaging  is  completed. 
The  plate  is  then  well  annealed. 

If  a  lower  plate,  the  second  or  strengthening  piece  is  swaged  and 
trimmed,  leaving  a  square  edge  extending  to  near  the  angle  of  the  rim. 
If  a  partial  lower  plate,  the  supplementary  piece  of  metal  is  adapted, 
annealed,  reannealed,  and  swaged  until  it  tits  the  die  perfectly  and 
exhibits  no  tendency  toward  alteration  of  form  when  heated  to  a  bright 
red.  The  upper  lingual  border  of  such  cases  is  carried  about  one-six- 
teenth of  an  inch  above  the  plate  line.  The  pieces  are  held  together  by 
means  of  binding  wire  and  soldered  with  pure  gold. 

The  plate,  thoroughly  annealed,  is  now  bound  firmly  to  the  die  with 
wire,  and  by  means  of  pliers  and  a  light  hammer  the  excess  of  plate 
extending  above  the  strengthening  piece  at  the  lingual  aspects  of  the 
teeth,  is  bent  over,  forming  a  slight  rim  not  more  than  one-sixteenth  of 
an  inch  broad.  After  the  swaging  is  completed  all  base-plates  for  con- 
tinuous gum  should  be  annealed  at  a  very  high  temperature. 

The  adaptation  of  the  plate  to  the  deepest  portions  of  the  die  is 
secured  through  the  use  of  chasers.  These  are  formed  of  old  tooth- 
brush handles  filed  to  a  wedge-shaped  edge. 

Instead  of  forming  a  posterior  rim  by  turning  over  that  portion  of 
the  plate,  some  operators  prefer  ^  adding  to  the  plate  a  combination  of 
wire  and  an  addition  of  plate  which  shall  serve  as  a  limiting  shoulder  to 
the  porcelain :  sloping  from  the  latter  there  is  a  ledge  of  platinum  which 
may,  by  altering  its  form,  increase  or  diminish  at  the  will  of  the  ope- 
rator the  pressure  of  that  portion  of  the  denture.  Aside  from  the 
removal  of  the  abrupt  termination  of  the  plate,  the  added  heel  subserves 
another  purpose — that  of  lessening  the  tendency  of  the  plate  to  suffer 
alteration  of  form  when  subjected  to  the  great  heat  of  the  furnace. 

The  addition  is  made  after  the  following  method :  Round  plati- 
num wire  of  No.  19  gauge  is  bent  to  fit  the  plate  along  a  line  extending 
from  the  alveolar  edge  of  one  side  to  that  of  the  other,  and  about  three- 

1  Method  of  Dr.  D.  D.  Smith. 


FORMING   THE  PLATE. 


451 


sixteenths  of  an  inch  from  the  posterior  edge  of  the  plate.  It  is  first 
attached  on  its  middle  by  means  of  a  small  piece  of  24-carat  gold.  The 
adaptation  of  the  remainder  of  the  wire  is  perfected,  and  it  is  attached 
throughout  its  length. 

A  piece  of  platinum  plate  No.  29,  wide  enough  to  cover  the  wire  and 
the  posterior  edge  of  the  plate,  and  extending  the  entire  length  of  the 
wire,  is  annealed  and  swaged.  It  is  better  to  lightly  swage  the  plate  with 
the  wire  attached  before  swaging  the  supplementary  piece.  As  soon  as 
the  outlines  of  the  wire  are  distinctly  marked  in  the  counter-die,  the  groove 
made  in  the  lead  is  deepened  by  means  of  a  chisel.  The  piece  of  plate 
is  annealed,  laid  in  position  in  the  counter-die,  and  swaged.  Reannealed, 
it  is  again  placed  in  the  counter-die,  the  plate  over  it,  and  they  are 
swaged  together.  The  same  precaution  is  taken  to  prevent  the  contact 
of  the  die  and  counter-die  metals  as  in  swaging  the  plate  proper.  The 
plate  extending  over  the  wire  and  the  posterior  edge  of  the  plate  is  cut 
away  until  it  is  flush  with  the  latter  and  half  covers  the  wire  (Fig.  536). 

Fig.  536. 


Showing  piece  of  plate  to  be  soldered  over  and  back  of  the  wire,  and  the  same  in  place 

on  the  plate. 

The  sections  are  bound  together,  24-carat  gold  placed  in  front  of  the 
wire,  and  heat  applied,  drawing  the  solder  under  the  wire  and  plate 
addition.  The  posterior  edge  is  now  smoothed  and  rounded.  The  plate 
is  next  boiled  in  a  1:3  solution  of  sulphuric  acid ;  then,  washed  with 
strong  soap,  is  ready  for  trial  in  the  mouth  and  securing  of  the  articulation. 
It  is  applied  to  the  plaster  model  first,  to  ascertain  that  its  adaptation  is 
correct :  if  found  to  be  accurate  here,  it  is  transferred  to  the  mouth  and 
the  patient  directed  to  draw  it  to  position.  Should  the  adhesion  be 
imperfect,  a  partial  adhesion  which  lessens,  the  sound  of  air  entering 
beneath  the  plate  being  distinctly  audible  in  some  cases,  it  is  first  ascer- 
tained that  the  plate  is  of  the  proper  length — that  it  does  not  impinge 
upon  the  tissues  affected  by  the  movements  of  the  muscles  of  the  soft 
palate.  Should  this  be  found,  the  disturbing  element,  the  plate,  is  cut 
away  the  proper  amount. 

Another  source  of  imperfect  adhesion  will  be  found  in  a  lack  of 


452  CONTINUOUS-GUM  DENTURES. 

accuracy  of  the  adaptation  of  the  plate  about  the  chamber.  A  sharp 
edge-graver  is  passed  around  the  chamber-piece  of  the  die,  and  a  chaser 
employed  to  drive  the  plate  into  the  angle  at  the  base  of  the  chamber. 

Occasionally  minute  perforations  may  exist  in  this  groove,  so  that  the 
precaution  is  taken  to  partially  fill  the  groove  with  melted  wax. 

Should  the  adhesion  be  not  yet  satisfactory,  an  examination  is  made 
to  locate,  if  there  be  any,  hard  areas,  upon  which  the  plate  may  be 
arrested  :  if  none  are  found  and  (if  present  they  should  have  been  seen 
and  allowance  made  for  them  in  forming  the  model),  it  is  inferred  that 
the  impression  itself  is  inaccurate,  so  that  a  new  impression  may  be 
necessary.  Should  the  adhesion  be  found  correct,  it  is  advised  by  some 
operators  to  exercise  pressure  by  means  of  an  excavator  at  all  parts  of 
the  plate,  and  if  unusual  yielding  of  the  underlying  tissues  be  found  in 
defined  areas,  the  corresponding  areas  of  the  die  are  scraped  away  and 
the  plate  reswaged,  until  by  trial  of  the  plate  in  the  mouth  it  is  found 
the  bearing  is  uniform.  In  the  majority  of  cases  a  plate  so  adapted  to 
an  accurate  model  that  it  does  not  rock  when  alternating  pressure  is 
applied  along  its  crest  will  require  no  alterations.  These  when  necessary 
are  to  be  made  by  means  of  burnishers  and  swaging,  never  by  bending, 
as  the  heating  of  the  piece  in  the  furnace  neutralizes  changes  made  by 
bending,  and  renders  them  of  no  avail. 

Articulation. 

The  wax-bite  is  taken  as  described  in  Chapter  XII.,  the  wax  being 
built  so  that  it  restores  the  lost  lip  and  cheek  contour,  the  middle  line 
of  the  face  marked,  and  the  length  of  the  teeth  represented  in  the  length  of 
the  wax.  The  wax  block,  thoroughly  chilled,  is  to  have  a  layer  of  softened 
wax  laid  over  its  end,  and  the  patient  instructed  to  bite  until  the  oppos- 
ing teeth  are  checked  by  coming  in  contact  with  the  hardened  contour 
Avax.  A  shade  tooth  is  taken,  always  testing  for  correspondence  in  color 
by  placing  the  tooth  under  the  lip.  Should  any  natural  teeth  remain, 
these  are  to  furnish  the  guide  as  to  the  shapes  and  sizes  of  the  artificial 
teeth ;  if  all  the  teeth  are  absent,  the  size,  form,  and  color  of  the  arti- 
ficial teeth  are  to  be  determined  by  the  physiognomy,  age,  and  tempera- 
ment of  the  patient.  As  this  class  of  prosthesis  represents  the  acme  of 
dental  art  as  far  as  plate  dentures  are  concerned,  this  step  of  its  con- 
struction must  receive  the  attention  its  importance  merits. 

A  distinctive  variety  of  tooth  mould  is  designed  for  the  forming  of 
the  teeth  for  continuous-gum  work  (Fig.  537).  The  teeth  are  made  with 
long  porcelain  extensions  corresponding  with  the  roots  ;  they  are  designed 
to  ensure  the  tooth  resting  upon  the  platinum  plate,  no  matter  what 
length  may  be  required.  Their  pins  are  single,  placed  beneath  the  shoul- 
der ;  they  are  designed  to  limit  the  extent  of  the  artificial  gum,  and  are 
sufficiently  long  to  serve  to  hold  the  tooth  to  its  future  backing.  When 
the  teeth  are  to  be  unusually  short,  teeth  designed  for  mounting  upon 
celluloid  or  vulcanite  may  be  employed.  The  teeth  are  selected  the 
proper  shape,  shade,  and  size,  being  long  enough  to  extend  from  the 
plate  to  the  length  marked  on  the  wax,  which  length  has  been  noted  by 
scratching  the  model  with  a  pair  of  dividers. 

In  selecting  the  teeth  the  operator  may  at  will  follow  any  individual 


ARTICULATION.  453 

indications  of  the  case  in  hand  :  the  cuspids  may  be  selected  more  yellow 
than  the  incisors  ;  the  shade  of  a  bicuspid  may  be  different  from  that 
of  the  adjacent  teeth,  etc. 

Fig.  537. 


Teeth  for  continuous-gum  dentures. 

If  the  models  are  mounted  upon  the  common  hinged  articulator,  its 
set-screw  is  placed  at  its  proper  length.  If  a  Bonwill  articulator  be 
employed,  the  posterior  portions  of  the  wax  are  permitted  to  remain 
until  the  anterior  teeth   have  been  articulated  and  arranged. 

Any  irregularities  in  the  positions  of  the  teeth  known  to  have  been 
present  with  the  natural  organs  may  be  reproduced  in  the  artificial  teeth. 
Occasionally  the  positions  and  arrangement  of  the  occluding  teeth  will 
form  a  valuable  guide  in  this  particular. 

The  centrals  are  first  set,  the  amount  of  grinding  necessary  to  bring 
the  cutting  edges  of  the  teeth  at  their  proper  lengths,  with  the  artificial 
roots  resting  firmly  upon  the  plate,  noted  and  done.  The  remaining 
teeth  are  set  to  accurate  <jcclusion  and  arranged  in  artistic  correspondence 
with  the  indications.     (See  Evans'  specimens  in  chapter  on  Celluloid.) 

The  forms  of  these  teeth  permit  a  wide  latitude  in  their  arrange- 
ment, and  the  operator's  taste  may  make  of  this  and  the  succeeding 
operations  mere  dental  carpentry  or  a  fine  art. 

The  teeth,  after  the  arrangement  is  completed,  are  attached  to  the 
plate  by  means  of  adhesive  wax.  Wax  is  moulded  over  the  buccal  and 
labial  walls  of  the  plate,  covering  the  necks  of  the  teeth  :  it  is  built  and 
carved  after  the  desired  form  of  the  natural  gum. 

The  piece,  now  placed  in  the  mouth,  is  to  have  the  articulation  tested  : 
if  this  is  found  correct,  any  alterations  in  the  arrangement  of  the  teeth 
which  the  artistic  sense  of  the  operator  may  suggest  are  made.  The 
gum  contour  is  noted  :  if  more  wax  be  required  in  places  to  restore  the 
lost  facial  contour,  it  is  added,  and,  vice  versa,  wax  is  carved  away  where 
necessary.  The  contour  of  a  finishing  piece  requiring  extensive  restora- 
tion is  shown  in  Fig.  538.  The  primary  wax  serves  as  a  guide  in 
forming  the  contour. 

The  piece  is  transferred  to  the  model :  the  surfaces  of  the  latter  and 
of  the  wax  and  teeth  are  oiled,  and  a  plaster  wall  formed  which  shall 
serve  as  a  guide  in  moulding  the  contour  of  the  piece  in  porcelain. 
When  set  this  is  removed,  the  wax  detached,  teeth  drawn  from  their 
beds,  they  and  the  plate  boiled  in  the  sulphuric-acid  solution.  The 
teeth  are  returned  to  the  wall,  which  is  then  adjusted  to  the  model,  and 


454  CONTINUOUS-GUM  DENTURES. 

the  teeth  are  cemented  to  the  plate  by  means  of  adhesive  wax.     When 
the  wax  is  hard  the  walls  are  detached  and  the  articulation  tested.     The 

Fig.  538. 


Continuous-gum  set  tinished  with  plumpers. 

surfaces  of  the  teeth  to  be  embraced  in  the  investment  are  to  receive  a 
coating  of  thick  shellac  varnish.  Owing  to  the  high  temperature 
required  to  fuse  24-carat  gold  (the  solder),  the  enamel  of  the  teeth  is  in 
danger  of  fusing  with  portions  of  the  investment  if  this  precaution  of 
varnishing  the  teeth  is  not  taken.  The  shellac  burns  out  in  heating,  so 
that  a  space  is  left  between  each  tooth  and  the  investment,  and  their 
contact  is  thus  avoided. 


Investing,  Backing,  and  Soldering. 

Investing. — The  investing  material  consists  of  asbestos  and  plaster. 
One  part  of  coarse-ground  asbestos  is  placed  in  a  bowl,  the  asbestos  is 
covered  by  water,  so  that  its  particles  are  distinct ;  plaster  is  sifted  in 
imtil  the  water  is  saturated,  when  the  mixture  is  stirred  well.  The 
case  is  wet ;  the  interior  of  the  plate  is  filled  with  the  mixture ;  a  layer 
some  one-half  an  inch  thick  is  placed  upon  a  glass  slab  and  the  invest- 
ment in  the  plate  joined  to  it ;  the  investment  is  built  about,  between, 
and  over  the  teeth  to  a  depth  of  about  an  inch.  Some  operators  prefer 
to  add  sand  to  the  asbestos  and  plaster  for  investing.  This  lengthens 
the  time  necessary  for  proper  heating  and  cooling,  tends  to  increase  the 
tendency  of  the  investment  to  fracture,  and  not  infrequently  particles 
of  sand  fuse  to  the  enamel  of  the  teeth.  The  writer  believes  checking 
and  cracking  of  the  teeth  to  be  more  frequent  with  sand  than  with 
asbestos  as  a  material  for  investing. 

When  the  investment  is  hard,  the  adhesive  wax  is  picked  away  from 
the  plate  and  the  teeth,  and  each  pin  is  bent  at  a  right  angle  with  the 
axes  of  its  tooth  (Fig.  539). 

Backing. — Much  of  the  strength  of  a  continuous-gum  piece  depends 
upon  the  proper  backing  of  the  teeth.  The  backing  stays  for  the  entire 
denture  are  made  in  three  sections — one  serving  to  stay  the  anterior 
teeth,  one  on  each  side  supports  the  molars  and  bicuspids. 

Patterns  are  made  of  stiflF  paper,  following  at  their  inferior  edges 
the  outlines  of  the  plate,  and  fitting  beneath  the  pins  of  the  teeth  at  its 
upper  edge.  The  pattern  for  the  stays  of  the  anterior  teeth  is  to  extend 
beneath  the  pins  of  the  first  bicuspids  of  both  sides. 

These  patterns  are  exactly  reproduced  in  platinum  No.  29,  which  is 
well  annealed.     The  anterior  section  of  the  stays  is  adapted  first :  it  is 


INVESTING,  BACKING,  AND  SOLDERING. 


455 


bent  to  fit  under  the  pins  of  the  teeth,  to  conform  to  the  palatal  sur- 
faces of  their  roots,  and  to  be  in  close  contact  with  the  plate  at  its  base. 
The  pins  of  the  six  anterior  teeth  are  now  bent  over  the  stay,  holding 
it  firmly  against  these  teeth  ;  the  pins  of  the  first  bicuspids  are  not  bent 


Fig.    539. 


Plate  and  teeth  invested  for  backing  and  soldering. 


down  until  the  posterior  sections  of  the  stays  are  fitted,  when  all  the  pins 
are  bent  over,  holding  the  stays.  Fracture  of  continuous-gum  pieces 
occurs  perhaps  more  frequently  at  the  sites  of  the  first  bicuspids  than  in 
other  parts :  the  double  backing  at  these  points  will  therefore  serve  to 
strengthen  a  weak  part. 

The  writer  advises  against  perforating  the  stays,  as  practised  in  some 
laboratories  :  it  serves  no  good  purpose,  and  notably  weakens  the  stays. 

Soldering-. — Borax  rubbed  into  a  paste  with  water  is  painted  along 
the  junction  of  each  pin  with  the  stay,  and  along  the  base  of  the  stays. 
The  borax  is  applied  not  as  a  flux,  as  the  non-oxidizable  metals  (pure 
platinum  and  24-carat  gold)  require  no  flux,  but  as  a  means  for  holding 
the  pieces  of  solder  in  contact  with  the  parts  upon  which  they  are  placed. 
24-carat  gold  of  No.  26  gauge  is  cut  in  small  squares,  one  for  each  pin, 
about  one-sixteenth  of  an  inch,  the  pieces  for  uniting  the  stays  with  the 
plate  about  one-eighth  of  an  inch  square  ;  12  grains  or  but  little  more  of 
24-carat  gold  should  be  used  to  solder  the  piece.  A  square  of  solder  is 
laid  beside  each  bent-over  pin,  and  the  larger  squares  set  upon  the  plate 
at  the  junction  of  the  stays. 

The  case  is  heated,  as  for  any  soldering  operation,  gradually  :  when 
the  body  and  walls  of  the  investment  are  at  a  red  heat  the  piece  is  trans- 
ferred to  a  charcoal  bed  and  heated  until  the  porcelain  teeth  and  platinum 
plate  are  at  a  red  heat,  when  a  pointed  flame  is  directed  against  the  solder, 
uniting  the  several  pieces.  It  is  to  be  noted  that  each  pin  is  perfectly 
soldered  to  the  stays,  adding  more  solder  where  necessary. 


456  CONTINUOUS-GUM  DENTURES. 

When  the  plate  and  teeth  are  cool  the  investment  is  carefully  broken 
away,  and  the  denture  boiled  in  sulphuric-acid  solution  until  every  trace 
of  borax  is  removed.  Borax  exercises  a  deleterious  influence  in  that,  if 
not  thoroughly  removed,  it  causes  blisters  upon  the  surface  of  the  finished 
piece.  This  effect  has  been  attributed  to  an  excess  of  gold  used  in  the 
soldering,  but  after  a  series  of  experiments  the  writer  has  come  to  the 
opinion  that  the  blistering  is  always  due  to  borax  which  has  been  per- 
mitted to  remain  after  soldering. 

The  case  is  washed  with  strong  soap,  then  in  water,  and  dried.  It  is 
now  placed  upon  the  plaster  model,  to  which  it  should  be  perfectly 
adapted ;  removed  to  the  finishing  die  if  necessary,  and  coaptation  per- 
fected there.  The  articulation  is  tested  :  should  any  of  the  teeth  have  been 
disturbed  in  soldering  or  in  removing  the  investment,  they  are  returned 
to  position.  The  case  is  now  scrubbed  until  scrupulously  clean,  alcohol 
poured  over  it,  and  it  is  placed  where  free  from  the  access  of  even 
dust. 

The  subsequent  operations  relating  to  the  ceramic  aspect  of  this  work 
depend  for  their  success  or  failure  upon  the  observance  or  non-observance 
of  technicalities  concerned  in  the  management  and  care  of  the  furnace  in 
which  the  porcelain  is  fused,  and  the  methods  of  attaching  and  to  fusing 
the-  three  coatings  of  mineral  pastes. 

Until  within  the  last  fifteen  years  the  difficulty  and  annoyance  of 
construction  of  this  variety  of  denture  were  rightly  attributed  to  the  un- 
wieldy furnaces  employed  and  the  difficulty  of  maintaining  the  correct 
amount  and  distribution  of  heat.  The  introduction  of  improved  furnaces 
— first  in  point  of  time  that  devised  by  the  late  Dr.  Ambler  Tees — has 
lessened  the  former  difficulties,  and  the  substitution  of  coke  for  coal  as 
fuel  has  removed  one  of  the  greatest  of  annoyances,  i.  e.  gasing  of  the 
porcelain  by  the  ignited  gases  which  find  a  passage  through  the  pores 
or  cracks  in  the  muffles. 

Several  varieties  and  designs  of  gas  furnaces  may  now  be  had,  which 
lessen  the  already  lessened  annoyance  of  fire-tending.  The  introduction 
of  the  electric  furnace  of  Dr.  Custer  removes,  when  the  52  or  110- volt 
current  can  be  introduced,  the  last  laboratory  objection  urged  against 
continuous-gum  work. 

As  coke  is  almost  universally  obtainable,  the  coke  furnace  will  be 
first  described. 

The  variety  used  by  the  writer  for  several  years  is  that  known  as  the 
^'  Tees  "  lilliput  furnace.  It  is  made  of  fire  clay,  bound  around  with 
strap  iron.  The  furnace  is  in  three  sections.  The  upper  section,  form- 
ing the  lid,  is  perforated  in  its  top  for  the  adjustment  of  the  draught- 
pipe  ;  in  front  is  a  semicircular  opening,  with  a  closely-fitting  stopper : 
this  is  the  fuel  opening.  The  second  section  contains  the  muffle,  its 
anterior  extremity  resting  upon  a  ledge,  its  posterior  received  into  a 
depression  moulded  in  the  surface  of  the  posterior  wall  of  the  furnace. 
The  chamber  about  the  muffle  contains  the  greater  part  of  the  fuel.  The 
under  section  contains  the  grate  and  the  ash-pit.  The  entire  furnace  is 
but  fifteen  and  a  half  inches  high,  twelve  inches  wide,  and  eight  inches 
deep ;  the  walls  are  one  inch  thick.  Though  the  size  of  the  furnace  is 
much  less  than  preceding  forms  of  furnaces,  a  temperature  may  be  ob- 
tained in  the  muffle  sufficiently  high  to  fuse  all  grades  of  porcelain. 


PEEPABINO    THE  FUEL. 


457 


A  special  poker  and  pair  of  tongs  are  indispensable  adjuncts  for  the 
proper  management  of  the  fire. 

The  furnace  should  be  kept  in  a  dry  room  to  ensure  against  oxida- 
tion and  consequent  destruction  of  the  iron  strappings.     It  is  not  neces- 


FiG.  540. 


LiUiput  furnace. 

sary,  as  with  the  old  forms  of  coal  furnaces,  that  the  furnace  be  placed 
in  the  cellar  to  procure  sufficient  draught :  this  may  be  obtained  with  a 
much  shorter  length  of  chimney. 

The  furnace  is  set  upon  a  small  table,  resting  upon  bricks  placed 
under  its  side  ends  ;  the  back  of  the  furnace  is  at  some  distance  from 
the  wall.  The  rim  surrounding  the  chimney  opening  has  placed  over  it 
stovepipe  which  is  connected  with  the  wall  chimney,  as  shown  in  Fig. 
540. 

Preparing  the  Fuel. 

What  at  a  casual  glance  might  appear  a  detail  of  small  moment  is 
the  lighting  and  maintaining  the  fire,  and  yet  it  is  one  of  essential  im- 
portance. The  pieces  of  coke  should  be  of  a  size  which  shall  permit 
the  free  circulation  of  air  between  them,  and  yet  be  small  enough  to  sup- 
port the  heated  muffle,  oifering  a  large  heating  surface  to  the  latter. 
Pieces  of  white  pine,  about  one  inch  thick,  are  cut  in  lengths  of  four 
inches.  Selected  coke  is  broken  and  all  pieces  chosen  about  the  size  of 
walnuts  :  about  three-quarters  of  a  peck  of  these  pieces  will  suffice  for 
one  heating.  The  furnace  is  filled  to  the  top  of  the  muffle  with  shav- 
ings or  paper,  and  some  half  dozen  pieces  of  wood  are  thrown  upon  the 
shavings,  which  are  then  ignited  from  the  top,  and  the  upper  stopper  is 
placed  in  the  top  opening ;  enough  wood  is  added  to  fill  the  furnace  to 


458  CONTINUOUS-OUM  DENTURES. 

the  upper  opening.  When  the  latter  is  thoroughly  ignited,  it  is  worked 
well  under  the  muffle  by  means  of  the  poker,  and  two  shovelfuls  of 
coke  are  thrown  upon  the  wood.  The  stopper  is  replaced  and  the  coke 
permitted  to  burn  for  ten  minutes,  when  the  stopper  is  removed  and  the 
coke  worked  down  to  the  grate,  raking  out  now  the  ashes  and  uncon- 
sumed  wood.  An  additional  shovelful  of  coke  is  placed  on  each  side 
of  the  muffle  and  worked  well  under  the  latter  with  the  poker.  It  is 
necessary  that  the  greatest  possible  amount  of  coke  should  be  in  contact 
with  the  under  surface  of  the  muffle  to  ensure  the  requisite  degree  and 
duration  of  heat.  The  body  of  the  furnace  is  filled  to  a  trifle  above  the 
base  of  the  upper  opening.  The  muffle  should  now  exhibit  no  visible 
evidence  of  being  heated  :  it  is  at  this  temperature  that  the  case  is  intro- 
duced for  the  initial  heating.  The  fire  is  forced  by  closing  the  upper 
opening  and  removing  the  draught-stopper  at  the  base. 

Each  subsequent  heating  requires  a  full  charge  of  coke,  so  that  should 
the  furnace  be  in  continuous  use  throughout  the  day,  the  fire  is  per- 
mitted to  smoulder  until  nearly  all  the  coke  is  consumed,  when  the 
ashes  are  raked  away  until  only  a  layer  of  coke  remains  covering  the 
grate-bars  ;  over  this  ignited  coke  a  fresh  charge  of  coke  is  placed,  exer- 
cising the  same  precautions  as  to  its  proper  distribution  as  in  the  first 
charging. 

When  the  fuel  is  burnt  out  and  the  furnace  becomes  cool,  it  is  taken 
apart  in  the  three  sections,  and  all  clinkers  are  removed.  It  is  a  gen- 
eral practice  to  now  coat  the  interior  of  the  furnace  with  a  paste  of 
kaolin  and  water.  A  muffle  will  usually  withstand  from  nine  to  twelve 
heatings.  Should  examination  reveal  cracks  in  any  part  of  its  length, 
these  are  wet  thoroughly  and  filled  with  the  kaolin  paste. 

The  several  gas  furnaces  and  the  latest  development  in  heating 
devices,  the  electric  oven  of  Custer,  are  described  in  the  chapter  on 
Porcelain. 

The  Porcelain  Paste,  and  its  Manipulation. 

The  ceramic  art  in  continuous-gum  work  is  divided  into  three  stages 
of  the  manipulation  of  mineral  pastes,  each  of  which  subserves  a  definite 
purpose. 

The  least  fusible  mixture  is  that  first  applied  :  it  serves  as  the 
uniting  medium  between  the  teeth  and  the  plate,  outlining  roughly  the 
general  contour  of  the  finished  piece.  Its  degree  of  contraction  is  rela- 
tively great  as  compared  with  that  of  cooling  platinum,  so  that  precau- 
tions are  taken  to  neutralize  the  effect  of  this  contraction. 

The  second  body  is  employed  to  remedy  defects  and  deficiencies  of 
the  first  body  and  to  furnish  the  contour  to  the  denture. 

The  third  coat  is  an  enamel  which  when  fused  resembles  the  natural 
gum  in  color,  and  presents  a  smooth,  glassy  surface. 

For  the  proper  manipulation  of  the  porcelain  paste  and  its  aesthetic 
carving  the  set  of  spatulas  illustrated  (Fig.  541)  will  be  found  almost 
indispensable  in  placing  the  paste  and  carving  during  the  several  stages 
of  the  work. 

No.  1  is  used  in  moulding  the  body  and  enamel  between  the  necks 
of  the  teeth  ;  No.  2  to  carve  the  festoons  and  the  margins  of  the  arti- 


FIRST  BAKING. 


459 


ficial  gum ;  No.  3  for  dividing  the  first  coat  of  body  into  segments, 
each  having  its  own  centre  of  contraction ;  No.  4  for  applying  and 
evenly  distributing  the  general  body  of  the  enamel. 

In  the  subsequent  manipulations  scrupulous  clean- 
liness must  be  observed  ;  the  plate  and  teeth  must  be  Fig.  541. 
entirely  free  of  any  particles  of  foreign  materials,  f\  ^  C\ 
even  from  dust ;  these  if  not  removed  may  cause 
blemishes  in  the  finished  pieces.  Indeed,  it  is 
desirable  that  the  porcelain  powders  should  be  made 
into  paste  with  distilled  water. 

A  teaspoonful  of  the  body  powder  is  placed  in  a  small 
porcelain  dish  and  made  into  a  mixture  with  water,      Is      ^  //  V 

the  consistence  of  the  mixture  to  be  about  that  of 
soft  putty.  In  examining  the  denture  in  its  present 
stage,  if  any  tooth  is  short  of  contact  with  the  plate, 
small  pieces  of  thin  platinum  plate  are  bent  and  fitted 
to  the  spaces  ;  these  are  to  prevent  movement  of  the 
teeth  due  to  the  contraction  of  the  fused  body.  It 
has  been  recommended  that  the  surface  of  the  plate 
be  scratched  by  means  of  a  sharp  excavator  point  to  ||||  |j!||  ||||  i|:i;i 
increase  the  adhesion  of  the  first  coat  of  body  to  the  12  3  4 
platinum ;  the  writer  deems  this  unnecessary. 

Small  portions  of  the  porcelain  paste  are  taken  upon  the  tip  of  the 
spatula  and  patted  into  close  contact  about  and  between  the  roots  of 
the  teeth  :  this  portion  of  the  body  is  to  be  insinuated  into  all  inter- 
stices before  any  attempt  is  made  to  apply  the  labial,  buccal,  or  palatal 
portions  of  body  ;  when  more  body  is  added,  with  each  considerable  addi- 
.tion  the  edge  of  the  plate  is  tapped  with  the  handle  of  the  spatula  to 
ensure  compactness  of  the  porcelain  paste  :  the  excess  of  water  rising  to 
the  surface  is  absorbed  by  bibulous  paper  or  muslin.  The  paste  covering 
the  lingual  surface  of  the  plate  should  have  about  the  thickness  of  No.  22 
plate.  The  body  is  applied  over  the  roots  to  almost  the  contour  desired 
in  the  finished  piece  ;  the  festoons  about  the  teeth  are  to  be  neatly  carved 
and  clearly  outlined.  AVhen  sufficient  body  has  been  applied  and  properly 
trimmed,  spatula  No.  3  is  employed  to  mark  the  body  into  definite  blocks, 
each  containing  one  of  the  artificial  teeth.  The  spatula  is  passed  through 
the  body  until  the  latter  is  grooved  to  the  stay  and  plate ;  the  cuts  are 
continued  on  the  lingual  aspect  of  the  denture.  Every  particle  of  body 
is  to  be  removed  from  about  the  pins  of  the  teeth.  Spatula  No.  1  is 
employed  to  remove  all  that  portion  of  body  which  occupies  the  groove 
of  the  rim ;  this  is  done  to  permit  any  change  of  surface  which  it  may 
be  necessary  to  make  in  the  rim.  Each  section  of  body  as  it  shrinks  in 
fusing  will  have  no  tendency  to  disturb  the  positions  of  the  teeth.  The 
plate,  its  palatal  surface  and  rim,  and  the  crowns  of  the  teeth  are  care- 
fully brushed  free  from  any  adherent  particles  of  the  body.  This  is 
accomplished  by  means  of  a  camel's-hair  pencil  cut  square  midway  be- 
tween the  ends  of  the  hairs  and  their  entrance  to  the  quill. 

First  Baking. 

The  fire,  built  as  described  in  the  furnace,  is  temporarily  checked  by 
removing  the  upper  stopper  and  inserting  the  lower  one.     When  the 


460  CONTINUOUS-GUM  DENTURES. 

muffle  becomes  dark  and  relatively  cool,  the  denture  is  set  upon  a  fire- 
clay slab  and  placed  at  the  mouth  of  the  muffle,  where  it  is  to  remain 
until  perfectly  dry.  If  heat  is  applied  suddenly,  the  body  is  forcibly 
detached  in  flakes  and  the  piece  is  damaged. 

Fig.  542. 


Showing  piece  after  first  baking. 

When  the  case  is  quite  dry  it  may  be  advanced  in  the  muffle  until 
within  about  one  and  a  half  inches  from  its  rear  end.  The  draft  is  now 
adjusted,  the  upper  stopper  being  inserted,  the  lower  removed.  When 
all  of  the  coke  has  ignited  and  the  muffle  itself  is  seen  to  be  at  a  bright 
red  heat,  the  muffle-stopper  is  applied,  and  the  heat  maintained  until  the 
body  is  fused.  It  is  important  that  this  first  coating  be  thoroughly 
fused,  as  it  is  the  layer  upon  which  the  strength  of  the  finished  pieces 
mainly  depends.  The  several  formulas  for  bodies  and  enamels  vary, 
and  all  have  different  fusing-points :  actual  test  is  the  only  method  by 
which  the  temperature  of  fusion  may  be  gauged,  so  that  no  general  rule 
can  be  given  as  to  the  length  of  time  a  piece  is  to  be  subjected  to  the 
maximum  heat. 

After  having  been  subjected  to  the  maximum  heat  for  about  ten  min- 
utes, the  case  may  be  withdrawn  from  the  muffle  and  examined  :  if  the. 
fusion  is  incomplete,  the  piece  is  returned  for  about  five  minutes  and 
again  examined.  The  denture  is  then  removed  from  the  furnace  and 
quickly  transferred  to  a  cooling  muffle,  where  it  is  permitted  to  remain  for 
about  thirty  minutes,  when  it  should  be  cool  enough  to  handle.  If  upon 
examination  any  tooth  or  teeth  may  be  found  to  have  suffered  change 
of  position,  it  is  bent  into  position  by  inserting  a  spatula-blade  in  one 
of  the  lines  of  division.  The  porcelain  section  is  to  be  held  in  its 
new  position  by  means  of  a  small  fragment  of  platinum  plate  wedged 
under  it. 

When  placed  upon  the  model,  sliould  it  be  found  that  the  plate  has 
suffered  any  change  of  form,  the  usual  change  being  a  narrowing  of  the 
alveolar  portions  of  the  plate,  readjustment  is  effected  by  using  a  block 
of  soft  white  pine  across  the  molars,  tapping  the  wood  with  the  horn 
mallet  until  the  adaptation  of  plate  to  the  model  is  correct.  It  is  to  be 
determined  now  the  extent  of  bending  which  shall  be  necessary  to  bring 
the  platinum  rim  at  its  proper  angle.  The  bending  is  done  by  means 
of  a  pair  of  flat  smooth  pliers  and  a  small  riveting  hammer  as  accessory 
when  found  necessary.  The  rim  is  dressed  to  a  uniform  width,  using  for 
the  purpose  small  smooth  files. 

The  case,  having  the  appearance  represented  in  the  illustration  (Figs. 
542,  543),  is  now  to  receive  the  second  coating,  known  as  the  second  body. 

This  layer  is  to  remedy  breaks  and  deficiencies  of  the  first  body  and 
to  furnish  the  contour  which  the  third  coating,  tlie  enamel,  sheathes. 


ENAMELLING. 


461 


Fig.  543. 


Shows  a  case  after  the  first  heating. 


An  exhaustive  familiarity  with  the  several  peculiarities  of  gum  out- 
lines and  rugffi  forms  is  of  extreme  utility,  as  furnishing  guides  to  the 
sesthetic  carving  of  the  second  body. 
The  operator  should  provide  him- 
self with  typical  models  of  cases 
illustrating  the  general  forms  asso- 
ciated with  the  temperaments  and 
with  the  physiognomic  peculiarities 
of  persons — what  type  of  gum  con- 
tour is  associated  with  what  forms 
of  teeth,  etc.  Accurate  plaster  mod- 
els of  typical  cases  will  be  found 
invaluable  in  this  connection.  The 
forms,  sizes,  and  distribution  of  the 
palatal  rugse,  anatomical  structures, 
rarely  considered  in  prosthetic  den- 
tistry, should  be  represented  in  the 
piece.  These  structures  perform  an 
office  in  deglutition  and  enunciation,^ 
and  should  not  be  ignored.  Their  presence  is  found  to  be  a  distinct 
source  of  comfort  to  the  patient. 

The  paste  of  the  second  body  is  made  as  the  first :  all  of  the  cracks 
in  the  first  body  are  filled,  the  spaces  about  the  pins  of  the  teeth  are 
filled,  the  labial  and  buccal  aspects  built  out  in  correspondence  with  the 
plaster  wall  formed  over  the  contour  wax  (see  above).  Maintaining  the 
required  fulness,  the  body  is  to  be  carved  into  appropriate  festoons.  The 
coating  over  the  lingual  surface  of  the  first  body  is  to  be  thin  ;  the 
rugse  are  to  be  represented  in  the  second  body,  defined  elevations  of  the 
material  being  placed  in  their  proper  positions.  After  the  carving  is 
completed  all  portions  of  the  denture  to  which  the  body  is  not  to  be 
fused  are  brushed  perfectly  free  of  any  adherent  particles.  The  fire  is 
to  be  prepared  as  for  the  first  heating ;  the  case  is  inserted  as  described. 
The  heating  of  this  coat  is  not  to  be  carried  to  a  state  of  smooth  fusion. 
It  is  carefully  watched,  withdrawn  occasionally,  and  when  the  surface  of 
the  body  has  an  appearance  resembling  No.  1  sand-paper  the  case  is 
removed  and  placed  in  a  cooling  muffle  for  thirty  minutes.  Should 
the  temperature  of  the  second  coating  be  carried  to  too  high  a  point,  it 
gives  a  dull,  dead,  lustreless  appearance  to  the  overlying  enamel. 

When  the  case  is  cool  it  is  placed  upon  the  model,  and  any  faults  of 
plate  adjustment  are  corrected  by  means  of  the  wooden  stick  and  mallet. 


Enamelling. 

The  mixture  for  the  third  coating,  that  of  the  enamel,  is  to  be  made 
thinner  than  for  the  preceding  layers.  The  denture  is  first  wet  to  facili- 
tate the  introduction  of  the  paste  into  the  crevices  of  the  piece,  particu- 
larly to  ensure  its  perfect  coaptation  beneath  the  rim  :  this  part  of  the 
work  must  be  carefully  attended  to,  or  else  there  is  danger  of  the  enamel 
flaking  in  the  furnace.  The  finer  gum  outlines  are  to  be  restored,  the 
layer  of  enamel  paste  to  be  about  the  thickness  of  No.  26  plate.  It  is 
1  Burchard,  Cosmos,  April,  1895. 


462 


CONTIN  UO  US-  G  UM  DENTURES. 


made  thinner  over  the  portions  representing  the  gum  covering  of  the 
roots,  so  that  a  lighter  shade  will  be  shown  at  these  parts,  this  being  in 
consonance  with  the  a2)pearance  seen  in  the  natural  gum. 

The  lines  and  shoulders  of  junctions  of  the  gums  with  the  teeth 
should  be  carved  with  the  utmost  nicety.  The  flow  of  the  paste  is  facil- 
itated by  dipping  the  spatula-blade  in  Avater. 

The  enamel  over  the  lingual  surface  of  the  piece  is  to  be  thinner 
than  over  its  buccal  and  labial  walls.  No  special  attempt  is  made  in 
clearly  outlining  the  rugse  in  the  enamelling  paste,  as  the  enamel  in 
fusing  distributes  itself  in  nearly  an  even  layer  in  the  depressions 
between  the  rugse :  however  the  paste  should  be  applied  in  a  very 
thin  layer  between  the  crests  ;  the  rugse  receiving  a  greater  depth  of 
coating. 

The  case  is  to  be  dried  very  slowly  at  the  mouth  of  the  muffle,  which 
should  be  dark.  The  slab  holding  the  denture  is  then  passed  to  the 
rear  of  the  muffle  and  the  full  draft  applied.  When  the  full  heat  is 
attained  the  case  is  examined  for  any  defects  caused  by  the  detachment 
of  portions  of  the  enamelling.  Should  any  be  found,  the  muffle-door  is 
closed  for  a  minute  or  two  to  effect  the  biscuiting  of  the  enamel.  The 
case  is  removed  and  placed  in  the  cooling  muffle  for  thirty  minutes. 
The  deficiencies  or  defects  are  remedied  by  the  addition  of  enamel  paste. 
A  fresh  fire  is  now  required  to  properly  fuse  the  enamel. 

Should  the  enamel  upon  examination  be  found  to  be  flawless,  the  muffle- 
door  is  to  remain  closed  for  from  eight  to  ten  minutes,  when  the  enamel 
glazes.  It  is  transferred  to  the  cooling  muffle,  where  it  is  to  remain 
until  cold.  If  upon  a  second  examination  any  defects  are  found,  these 
are  to  be  remedied  and  the  piece  again  heated  as  before. 

Fig.  544. 


The  completed  case. 

When  cool  the  denture  is  ready  for  finishing. 

The  rim  is  made  smooth  by  means  of  fine  files  :  all  file-marks  are 
removed  by  means  of  Arkansas  stone,  and  the  final  finish  given  with 
burnishers  and  soap.  The  palatal  surface  of  the  plate  is  cleansed  with 
powdered  pumice,  the  interior  of  the  chamber  being  burnished. 


REPAIRING   CONTINUOUS-GUM  DENTURES.  463 

Repairing  Continuous-gum  Dentures. 

The  repairing  of  continuous-gum  dentures,  while  undoubtedly  a  more 
tedious  and  lengthy  operation  than  the  repairing  of  other  classes  of 
artificial  dentures,  is  not  the  serious  drawback  to  its  employment  that 
some  have  stated.  They  may  be  readily  repaired,  and  at  the  completion 
of  the  operation  the  cases  are  as  strong  as  when  new,  and  exhibit  no 
indication  of  repair. 

When  cases  present  for  repair  they  have,  as  a  rule,  been  worn  for 
some  time  after  having  been  broken.  Each  piece  may  exhibit  cracks, 
irregularities,  and  possibly,  if  the  fracture  be  deep,  minute  spaces  may 
exist  between  portions  of  the  platinum  plate  and  the  porcelain.  Into 
these  spaces  the  secretions  of  the  mouth  and  more  or  less  food  debris  in 
a  state  of  minute  subdivision  gain  access.  These  must  be  entirely  re- 
moved before  any  attempt  is  made  at  fusing  new  porcelain,  for  if  this 
precaution  is  not  taken  the  vapors  generated  in  heating  may  ejfpand 
with  explosive  violence  and  detach  portions  of  the  porcelain. 

The  case  is  encased  in  an  investment  of  asbestos  and  plaster  about 
half  an  inch  thick.  When  hard,  the  investment  containing  the  denture  is 
placed  over  a  gas-stove  and  dried  ;  the  heat  is  raised  gradually  to  redness, 
which  carbonizes  the  foreign  materials.  The  piece  should  cool  gradually, 
and  then  be  washed  in  castile  soap  and  water. 

The  fire  is  prepared  in  the  furnace ;  the  case  is  placed  on  the  fire- 
clay slab,  introduced  into  the  muffle  while  it  is  still  dark,  gradually 
advancing  the  piece  until  it  is  as  hot  as  the  muffle,  when  the  draft  is 
applied  and  the  case  heated  to  redness,  effectually  decomposing  all 
foreign  materials  which  may  be  present  in  or  about  the  denture.  Re- 
moved to  the  cooling  muffle,  it  is  to  remain  for  about  half  an  hour. 

If  the  repair  is  to  be  of  a  tooth  or  teeth,  the  porcelain  and  any  rem- 
nants of  the  original  tooth  or  teeth  are  to  be  ground  away  to  the  depth 
and  curve  of  the  cervical  outline  of  the  teeth.  At  the  lingual  portion 
the  porcelain  is  ground  away  until  the  original  platinum  stay  is  exposed. 

Teeth  are  selected  of  the  mould  and  shade  of  those  on  the  denture, 
and  are  ground  to  fit  accurately  the  spaces  made  for  their  reception,  and 
waxed  in  position.  A  coating  of  shellac  is  applied  to  the  new  teeth, 
and  the  case  is  invested,  carrying  the  investment  over  the  tips  of  the 
teeth  so  that  they  will  be  held  in  position.  A  stay  is  fitted  under  the 
pins,  its  base  joining  the  old  stay ;  the  pins  are  bent  down  and  pure  gold 
is  applied  for  soldering.  This  soldering  is  to  be  done  in  the  furnace  : 
the  unequal  heating  involved  in  soldering  under  the  blowpipe  might 
endanger  the  integrity  of  the  piece.  The  case  is  introduced  into  the 
muffle,  and  as  soon  as  the  solder  flows,  uniting  the  tooth  to  the  stay  and 
the  latter  to  the  old  stay,  the  piece  is  removed  to  the  cooling  muffle, 
where  it  remains  until  the  denture  itself  is  scarcely  warm.  The  invest- 
ment is  removed,  and  the  case  washed  with  soap  and  water. 

It  is  rarely  necessary  to  apply  more  than  one  coating  of  body  for 
repaired  cases.  The  body  is  applied  as  before,  heated  to  the  granular 
stage  ;  a  second  heating  vitrifies  the  enamel  applied  as  a  second  coating. 

Should  a  case  be  damaged  beyond  simple  repair,  or  found  to  be  so 
full  of  defects  as  to  be  unfit  for  use,  the  ceramic  part  of  the  work  may 
be  done  anew  without  the  taking  of   a  new  impression  and   articula- 


464  CONTINUOUS-GUM  DENTURES. 

tion.  The  palatal  surface  of  the  plate  is  oiled  and  a  plaster  cast  run  in 
it.  When  this  is  hard  it  is  mounted  in  an  articulator  set  to  the  proper 
distance  :  the  tips  of  the  teeth  are  to  be  imbedded  in  soft  plaster  placed 
over  the  second  arch  of  the  articulator.  The  denture  is  heated  to  red- 
ness in  the  furnace  and  plunged  into  cold  water.  This  heating  and 
chilling  are  repeated  until  the  porcelain,  teeth  included,  may  be  readily 
detached,  leaving  the  platinum  plate  uninjured  and  the  stays  in  position. 
A  new  set  of  teeth  is  fitted  to  position,  the  stays  and  the  articulating 
model  furnishing  the  guides  for  their  adaptation.  These  are  soldered  as 
the  original  teeth,  the  porcelain  attached  as  described. 

Single  Teeth  attached  in  Blocks  by  Means  of  Continuous 

Gum. 

Cases  are  occasionally  seen  in  which  the  plain  teeth  as  procured  from 
the  manufacturer  are  of  the  correct  sizes,  forms,  and  colors,  and  yet  in 
order  to  effect  a  harmonious  restoration  of  gum  contour  gum  blocks  or 
single  gum  teeth  made  in  the  stock  moulds  are  inapplicable.  It  is  pos- 
sible in  such  cases  that  the  correct  gum  form  may  be  had  by  the  process 
of  continuous-gum  baking.  An  impression  is  taken,  and  a  model  made 
representing  accurately  the  space  to  which  the  teeth  and  artificial  gum 
are  to  be  applied.  The  outline  of  the  future  gum  is  to  be  marked  on 
the  model,  and  a  line  made  inside  the  cervical  outlines  to  be  occupied  by 
the  artificial  teeth  upon  the  palatal  aspect  of  the  model.  Dies  and 
counter-dies  are  made,  and  a  plate  of  No.  29  platinum  swaged  to  fit  the 
model  and  correspond  with  the  marked  lines.  An  articulating  model  is 
made ;  plain  teeth  are  selected — plate  teeth  if  the  future  plate  is  to  be 
of  gold  or  silver ;  rubber  teeth  if  it  is  to  be  of  vulcanite.  The  teeth 
are  arranged  and  articulated.  They  are  cemented  to  the  plate  and  in- 
vested in  asbestos  or  plaster.  A  stay  is  fitted  to  each  tooth,  and  the 
parts  united  as  for  continuous  gum-work,  with  24-karat  gold  as  solder. 
The  plate  returned  to  the  model,  the  body  and  enamel  are  successively 
moulded  to  the  plate  as  for  continuous-gum  work.  The  stays  and 
palatal  aspect  of  the  platinum  are  to  be  entirely  free  of  the  porcelain, 
as  these  surfaces  are  to  be  soldered  to  the  body  of  the  future  plate. 

The  edge  of  the  platinum  plate  is  bevelled  and  its  line  marked  on 
the  plaster  model.  A  film  of  wax  is  applied  over  this  line,  so  that  the 
die  will  be  raised  sufficiently  to  have  the  plate,  when  adapted  to  the  die, 
overlie  the  edge  of  the  platinum. 

Dentures  op  Continuous  Gum  Mounted  on  Vulcanite  Plates. 

It  was  stated  early  in  this  chapter  that  the  form  of  vault  known  as 
the  high  or  peaked  is  that  in  which  dentures  of  continuous  gum  afford 
the  least  satisfactory  results. 

The  lightness  and  accuracy  of  adaptation  to  be  had  with  plates  of 
vulcanite  may  be  combined  with  the  aesthetic  features  recommending 
continuous  gum.  The  model  is  prepared  for  swaging  the  type  of  rim 
fitted  for  a  continuous-gum  denture.  A  plate  is  swaged  to  fit  the 
alveolar  walls  and  form  a  rim  ;  the  plate  is  to  extend  for  about  a  half 
inch  over  the  palatal  portion  of  the  alveolar  wall.     Along  this  portion 


CONTINUOUS  GUM  MOUNTED   ON   VULCANITE  PLATES.       465 

of  the  plate  edge  platinum  wire  No.  19  is  to  be  fitted  and  soldered.  The 
platinum  plate  is  placed  on  the  model,  a  trial  plate  completed  by  means 
of  a  wax  base-plate,  and  an  articulation  is  taken.  Plain  teeth  of  the 
variety  designed  for  rubber  work  are  to  be  fitted ;  stays  are  adapted  to 
the  teeth  and  plate. 

The  porcelain  is  attached  to  the  labial  and  buccal  surfaces  as  with  a 
continuous-gum  piece.  The  palatal  portions  of  the  plate,  the  stays  and 
heads  of  the  pins,  are  left  uncovered. 

The  piece  is  now  adjusted  to  the  model,  the  base-plate  formed  of  wax. 
The  investment  in  the  flask  is  made  as  for  rubber  work ;  the  platinum 
plate  and  teeth  are  to  occupy  the  lower  section  of  the  flask.  In  finish- 
ing the  plate  the  vulcanite  is  cut  on  the  palatal  surface  to  show  a  sharp 
line  of  demarkation  at  the  line  of  junction  with  the  platinum  plate. 
This  method  is  especially  applicable  for  full  lower  cases  where  it  is 
probable  that  extensive  cutting  will  be  necessary  to  properly  adapt  the 
plate  to  the  mouth. 

Another  method  of  forming  a  continuous  porcelain  gum  above  plain 
teeth  is  occasionally  practised,  which  does  not  involve  the  making  of  a 
platinum  base-plate.  It  is  less  accurate  than  the  latter  method,  but  in- 
volves less  labor. 

Upon  a  trial-plate  of  wax,  teeth  designed  for  continuous-gum  work 
are  arranged.  The  appropriate  fulness  and  contour  are  given  the  gum 
portions  of  the  wax.  The  wax  is  chilled  and  the  palatal  portion  of  the 
plate  cut  away,  leaving  the  arch  of  wax  holding  the  teeth  in  position. 


Fig.  545. 


The  denture  and  wax  are  removed  from  the  model.  The  teeth  are  to 
receive  a  preliminary  coating  of  plaster  of  Paris,  painted  on  with  a 
camel's-hair  pencil. 

The  piece  is  now  invested,  the  crowns  of  the  teeth  downward,  in  a 
mixture  consisting  of  equal  parts  of  fine  silex,  asbestos,  and  plaster.  A 
horseshoe-shaped  bed  of  the  investing  material,  about  half  an  inch  tliick, 
is  placed  on  a  glass  slab,  in  which  the  occlusal  surfaces  of  the  teeth  are 
placed.     The  investment  is  built  about  the  wax  gum,  covering  it  to  a 

30 


466 


CONTINUOUS-GUM  DENTURES. 


Fig.  546. 


depth  of  half  an  inch  and  extending  well  over  its  edge.  When  the 
investment  is  hard,  it  is  cut  away  sufficiently  to  permit  of  its  easy  intro- 
duction into  the  furnace  muffle.  Boiling  (not  merely  hot)  water  is  poured 
into  the  investment,  washing  away  every  vestige  of  wax.  The  piece  is 
now  warmed  until  perfectly  dry  :  for  this  purpose  it  is  placed  in  the 
muffle.  When  cooled  sufficiently  to  handle  a  piece  of  half-round  iridio- 
platinum  wire  No.  19  is  fitted  around  the  arch,  resting  upon  each  tooth 
above  the  pins.  The  wire  held  firmly  in  position,  each  pin  is  to  be 
bent  over  it  so  that  it  is  immovable  (Fig.  545). 

The  walls  of  the  mould  being  oiled,  a  mixture  of  body  in  water  is 
made  and  thoroughly  packed  against  the  wall  left  vacant  by  the  removal 
of  the  wax.  The  mixture  is  to  be  well  packed  in  front  of  the  roots  ;  the 
body  is  made  flush  with  the  lingual  edges  of  the  teeth  at  the  sides  of  the 
roots ;  its  upper  edge  is  to  be  made  thin  and  bevelled.  Small  pieces  of 
pure  gold  are  placed  at  the  lines  of  junction  of  the  pins  and  wire,  and 
the  case  is  introduced  into  the  furnace  muffle.  When  it  is  ascertained 
that  the  gold  has  melted,  attaching  each  pin  to  the  wire,  the  muffle  door 
is  closed  until  the  body  is  fused  to  the  granular  stage.  When  the  in- 
vestment has  been  in  the  cooling  muffle  for  about  fifteen  minutes,  it  is 

plunged  into  boiling  water,  which  soon  dis- 
integrates it.  Any  particles  of  investing 
material  found  adhering  to  the  body  are 
ground  away. 

Any  defects  or  deficiencies  are  remedied 
by  further  applications  of  the  body  mix- 
ture, and  this  additional  coating  is  to  be 
fused  to  the  same  extent  as  the  first.  The 
enamel  is  next  applied  and  fused. 

Any  grinding  necessary  to  permit  the 
correct  adaptation  of  the  block  to  the 
model  is  done.  The  subsequent  operations 
are  those  of  vulcanite  work.  This  method, 
as  stated,  is  less  accurate  than  that  of  the 
porcelain  attachment  to  a  platinum  arch. 

In  making  continuous-gum  pieces  to 
be  mounted  upon  full  lower  plates  of  vul- 
canite the  model  is  to  have  a  plate  of  gutta- 
percha moulded  over  it :  this  is  varnished.  Dies  are  made,  upon  which 
a  plate  of  No.  32  platinum  is  constructed.  This  plate  set  over  the  gutta- 
percha, teeth  are  arranged  upon  it  and  a  continuous-gum  attachment 
formed.  The  platinum  plate  is  roughened  and  a  vulcanite  base  made 
(Fig.  546). 


Lower  set  of  continuous  gum  set  in 
vulcanite. 


FORMULAS  FOR  MAKING  BODY  AND  GUM  ENAMEL 
FOR  CONTINUOUS-GUM  WORK. 


The  following  formulas  are  the  result  of  a  series  of  experiments 
made  with  a  view  of  producing  a  porcelain  body  which  will  fuse  at  a 
lower  temperature  than  the  majority  of  bodies  and  enamels  commonly 


FORMULAS  FOB  MAKING  BODY  AND   GUM  ENAMEL,  ETC.  467 

used  in  the  continuous-gum  method,  possessing  at  the  same  time  strength, 
firmness  of  texture,  and  freedom  from  liability  to  crack  or  check  on 
cooling.  It  is  believed  that  if  the  proportions  herein  given  and  the 
rules  for  their  preparation  are  strictly  adhered  to,  a  porcelain  will  result 
which  may  be  relied  upon  to  thoroughly  fulfil  the  requirement  of  con- 
tinuous-gum materials. 

The  body  is  composed  of  feldspar,  glass  or  flux,^  and  kaolin,  colored 
with  titanium.  The  gum  enamel  is  composed  of  feldspar,  flux,  and 
gum  frit. 

The  composition  and  preparation  are  as  follows  : 

Body. — Take  of  finely-powdered  feldspar,  40  pennyweights ;  flux,  9 
pennyweights ;  kaolin,  3  pennyweights.  These  are  to  be  mixed  and 
ground  dry  for  half  an  hour,  and  placed  on  a  fire-clay  slide  previously 
coated  with  finely-ground  silica,  and  burned  in  a  muffle  to  a  state  of 
vitrification,  and  when  cool  broken  up  and  ground  until  it  all  passes 
through  a  No.  10  bolting-cloth  sieve. 

Gum  Enamel  for  Continuous-gum  Work. 

Flux 12  pennyweights. 

Feldspar 40  " 

Gum  frit'' 2 

(xrind  for  one  hour  and  fuse  thoroughly  on  a  fire-clay  slide  in  the  muf- 
fle of  the  furnace.  When  cold  break  into  small  pieces  and  grind  until 
the  powder  passes  through  a  No.  10  bolting-cloth  sieve,  after  which  6 
grains  of  gum  frit  are  to  be  added  to  each  ounce  of  the  enamel  powder 
and  mixed  with  a  spatula. 

Before  burning  the  material  upon  the  fire-clay  slide  the  latter  should 
always  be  coated  with  fine  silex  to  prevent  the  enamel  from  adhering  to 
the  fire-clay. 

^  See  directions  in  chapter  on  Porcelain,  page  223,  for  the  preparation  of  flux,  some- 
times called  dental  glass. 

■^  The  formula  and  directions  for  the  preparation  of  gum  frit  will  be  found  on  page 
221,  chapter  on  Porcelain  Teeth,  etc. 


CHAPTER    XIV. 
CAST  DENTURES  OF  ALUMINUM  AND  FUSIBLE  ALLOYS. 

By  C.  L.  Goddard,  A.  M.,  D.  D.  S. 


Cast-metal  Dentures. 

The  principle  of  casting  metal  dentures  has  long  been  recognized  as 
the  most  desirable  for  obtaining  accurate  adaptation.  In  order  to  obtain 
the  best  results  the  following  are  essential :  A  metal  or  alloy  which  has  (a) 
sufficient  strength  ;  (6)  which  will  not  deteriorate  in  the  mouth  ;  (c)  which 
will  have  no  deleterious  action  on  the  teeth  or  mucous  membrane ;  (d) 
which  is  light,  or,  in  other  words,  has  a  low  specific  gravity ;  (e)  which  in 
casting  will  take  a  sharp  impression,  or,  in  other  words,  follow  the  fine 
lines  of  the  mould ;  (/)  which  will  not  discolor  in  the  mouth  ;  (g)  which 
can  be  readily  attached  to  the  teeth  ;  (/i)  which  has  a  reasonably  low 
fusing-point ;  (i)  and  can  be  cast  in  an  easily  constructed  mould. 

Tin  is  the  chief  component  of  alloys  for  this  purpose.  Other  metals 
are  added  to  lower  its  specific  gravity,  control  shrinkage,  and  produce  a 
sharper  casting.  These  are  silver,  bismuth,  gold,  and  in  some  instances 
cadmium  and  antimony. 

Several  of  these  alloys,  such  as  Wood's,  Watt's, Weston's,  and  Moffatt's, 
are  proprietary ;  hence  their  composition  is  not  known  to  the  profession. 

Most  of  these  alloys  are  too  heavy  for  superior  dentures,  but  that 
objection  may  be  remedied  to  a  great  degree  by  casting  a  plate  only  and 
attaching  the  teeth  with  vulcanite. 

The  following  formulas  have  been  given  to  the  profession : 
Kingsley's  alloy,  tin,  16  ounces;  bismuth,  1  ounce. 
Reese's  alloy,  tin,  20  parts ;  gold,  1  part ;  silver,  2  parts. 
Bean's  alloy,  tin,  95  parts ;  silver,  5  parts. 

(For  aluminum  alloys,  see  page  147.) 

Cast  and  Investment. — As  the  use  of  all  these  alloys  depends  on 
making  the  cast  and  investment  of  a  material  which  will  not  crack  nor 
change  shape  in  drying,  one  description  will  answer  for  all. 

The  impression  is  taken,  as  usual,  with  plaster,  wax,  or  modelling 
compound,  according  to  individual  preference.  If  a  vacuum  chamber  is 
desired,  it  is  best  to  carve  it  in  the  impression,  so  that  the  pattern  will 
be  represented  in  the  cast,  or  the  central  portion  may  be  slightly  scraped 
so  as  to  make  an  undefined  chamber  over  the  hard  parts. 

The  cast  is  made  of  equal  parts  of  plaster  and  sand,  asbestos,  marble 
dust,  chalk,  or  whiting.  The  latter  is  best,  as  it  gives  the  smoothest 
casting.  The  same  material  is  used  for  investing.  A  vacuum  chamber 
pattern  may  be  made  on  the  cast,  as  thus  described  by  Dr.  Chupein  :  ^  "A 
piece  of  base-plate  wax  is  softened  and  neatly  moulded  over  the  entire 

^Am.e7-ican  System  of  Dentistry,  vol.  ii.  p.  683. 


CAST-METAL  DENTURES.  469 

face  of  the  model.  The  paper  pattern  of  the  vacuum  chamber  is  laid  on 
the  wax  in  the  position  it  is  to  occupy  and  the  form  is  traced  on  it.  The 
pattern  is  then  lifted  off,  and  this  part  of  the  wax  is  cut  out  with  a  warmed 
wax-knife,  leaving  the  model  exposed.  The  exposed  part  of  the  model 
is  then  roughened  and  well  moistened  with  water,  and  plaster  of  Paris 
and  pumice-stone  (or  whiting),  mixed  in  the  same  proportions  as  for  the 
model,  are  incorporated  with  water  and  poured  into  the  space  made  by 
cutting  away  the  base-plate  as  has  been  described.  When  this  has  set  so 
as  to  be  quite  hard,  the  wax  base-plate  is  softened  and  lifted  from  the  cast. 
The  vacuum  chamber  model  is  then  scraped  down  to  the  proper  thickness." 

The  central  part  of  the  lingual  surface  of  the  cast  may  be  raised  by 
adding  with  a  camel's-hair  brush  a  thin  mixture  of  plaster,  whiting, 
and  water,  and  thus  a  pattern  made  for  an  "  undefined  chamber." 

For  a  base-plate  use  sheet  wax,  wax,  and  paraffin  or  modelling  com- 
pound, rolled  to  one-twentieth  or  one-twenty-fourth  of  an  inch  in  thick- 
ness. This  is  easily  done  by  means  of  a  smooth  board  and  a  roller  or 
section  of  a  broomstick.  Wet  both  board  and  roller.  Warm  a  sheet  of 
wax  and  roll  it  out  quickly. 

Beads. — The  cast  plate  is  the  only  metal  plate  upon  which  a  bead  may 
be  formed  on  the  palatine  surface.  Such  a  bead,  condemned  by  many, 
has  been,  in  the  writer's  experience,  very  valuable  in  cases  in  which  the 
mucous  membrane  was  very  soft.  Such  a  bead,  made  around  either  a 
defined  or  an  undefined  chamber  or  around  the  plate  about  one-sixteenth 
of  an  inch  from  the  palatine,  buccal  and  labial  borders,  imbeds  itself  in 
the  soft  tissues  and  acts  as  a  valve  to  keep  the  air  from  under  the  plate. 
The  writer  recalls  one  partial  case  in  which  the  plate  fitted  per- 
fectly, but  would  stay  in  place  but  a  few  minutes,  the  patient  being 
conscious  of  the  air  entering  under  it.  A  cast  was  made  in  this  plate, 
and  a  new  plate  made  which  differed  from  the  first  only  in  a  bead  which 
surrounded  the  chamber  at  the  distance  of  about  one-eighth  of  an  inch. 
The  second  plate  was  a  complete  success. 

To  make  such  a  bead  use  a  small  scoop  excavator,  and  make  a  round- 
bottomed  groove  in  the  cast  wherever  the  bead  is  needed.  Sometimes 
the  device  is  of  advantage  across  the  plate  about  an  eighth  of  an  inch 
from  the  posterior  border.     (See  chapter  on  Vulcanite.) 

The  thin  wax  base-plate  is  more  easily  adapted  to  the  east  if  both  are 
immersed  in  warm  water  and  the  wax  moulded  on  the  cast  with  thumbs 
and  fingers.     By  then  immersing  in  cold  water  the  wax  is  made  rigid. 

On  this  base-plate  the  teeth  are  mounted  as  in  rubber 
work,  and  the  plate  contoured  according  to  the  needs  of  _  * 

the  case.  The  smallest  possible  quantity  of  wax  should 
be  used,  as  it  is  to  be  remembered  that  the  metal  alloy 
which  takes  its  place  is  much  heavier  than  vulcanite. 

Teeth    for  vulcanite  work   are    best   adapted  for  this 
work,   but  if  the  pins  are    very   prominent  they   should  _ 

be  bent  nearer  the  necks  of  the  teeth  to  avoid  excess 
of  metal  plate. 

In  partial  cases  of  close  bite  a  tooth  may  be  backed  with  gold  or 
silver  and  the  backing  extended  half  an  inch  or  more  into  the  wax- 
plate  (Fig.  547).  This  projecting  portion  should  be  roughened  or 
have  holes  punched  in  it  for  better  retention  in  the  alloy. 


470     CAST  DENTURES   OF  ALUMINUM  AND  FUSIBLE  ALLOYS. 

If  gum  teeth  or  blocks  are  used,  grind  off  the  thin  upper  portion 
of  the  gum  at  right  angles  or  at  a  slightly  obtuse  angle  with  the  labial 
surface.  This  is  to  prevent  fracture  by  contraction  of  the  metal  when 
cooling. 

As  the  thin  wax  advised  for  a  base-plate  is  readily  bent  out  of  shape, 
it  is  better  to  u,se  a  more  rigid  base-plate,  preferably  of  modelling  com- 
pound, for  taking  the  bite  and  mounting  the  teeth.  After  trying  in  the 
mouth  and  making  any  necessary  change  in  position  of  the  teeth,  put 
the  case  on  the  cast,  and  stick  it  there  securely  by  melting  the  wax 
around  the  upper  border  of  the  plate  with  a  hot  spatula,  adding  sticky 
wax  temporarily  in  convenient  places.  With  a  hot  spatula  cut  out  the 
thick  base-plate  from  the  lingual  portion  and  substitute  a  layer  of  thin 
wax  about  No.  23  B.  &  S.  G.,  or  two  or  three  layers  of  the  thin  wax 
sheets  used  in  making  artificial  flowers.  Smooth  the  wax  around  the 
necks  of  the  teeth  ready  for  flashing. 

Fig.  548. 


Weston's  improved  flask. 


In  some  cases  in  which  the  necks  of  the  teeth  rest  on  the  cast  it  is 
best  to  imbed  the  case  in  the  lower  half  of  the  flask  before  substituting 
thin  wax  for  the  lingual  portion. 


CAST- METAL  DENTURES. 


471 


After  the  wax  is  made  as  smooth  as  possible  it  may  be  given  a  gloss 
with  slight  puffs  of  the  blowpipe  flame.  Figs.  548  and  549  show  flasks 
used  for  this  work. 

The  object  of  the  length  is  to  give  room  for  a  long  gate,  so  that  a 
column  of  the  metal  as  it  is  poured  in  will  force  the  lower  portion  into 


Fig.  549. 


Watt's  moulding-flask. 

all  the  intricate  parts  of  the  mould.  For  this  reason  the  case  should 
occupy  the  lower  end  of  the  flask.  Lay  the  lower  half  of  the  flask  on  a 
smooth  surface,  such  as  glass  or  wood  covered  with  paper  or  waste  rub- 
ber dam.  The  latter  is  best,  as  it  separates  easily  from  the  plaster. 
Invest  as  for  vulcanite  work,  but  with  the  same  material  used  in  making 
the  cast.  Trim  the  investing  material  so  that  the  mould  will  "  part "  at 
the  upper  border  of  the  wax  base-plate. 

Cut  pouring  and  vent  gates  half  the  desired  depth.  These  will  differ 
according  to  the  flask  used.  Use  a  small  vulcanite  scraper.  With  the 
Weston  flask  begin  at  the  pouring  gate  at  the  upper  end  of  the  flask, 
and  cut  the  gate  of  the  same  size,  but  decrease  it  gradually  for  about 
half  the  distance  to  the  mould  ;  then  for  an  upper  denture  broaden  the 
gate  till  at  the  posterior  border  of  the  mould  it  is  about  an  inch  wide 
and  not  much  deeper  than  the  thickness  of  the  wax  base-plate. 

For  a  lower  denture  extend  the  gate  about  three-sixteenths  of  an 
inch  wide  till  it  reaches  the  mould  in  the  region  of  the  incisors.  Cut 
two  other  gates  in  each  side  from  the  main-gateway,  one  to  each  end  of 
the  mould  and  one  to  the  region  of  the  bicuspids. 

When  the  Watt  flask  is  used  (Fig.  550)  two  gates  are  cut,  one  from 
each  "heel"  of  the  plate  to  the  funnel  opening  above  it;  one  of  these  is 
made  small  all  the  way,  and  the  other,  small  at  the.  beginning,  should 
increase  in  size  till  at  the  top  it  equals  that  of  the  funnel. 

Coat  the  investing  material  in  the  lower  half  of  the  flask  with  a  thin 
mixture  of  whiting  or  chalk  and  water ;  varnish  it  with  thin  shellac 
varnish  or  rub  it  with  pulverized  soapstone.  The  object  is  to  fill  up  the 
pores  and  prevent  adhesion  of  the  investing  material.     Add  the  second 


472     CAST  DENTURES  OF  ALUMINUM  AND  FUSIBLE  ALLOYS. 

half  of  the  flask  and  fill  carefully  with  investing  material,  tapping  the 
rim  slightly  to  make  any  air-bubbles  which  may  be  present  rise  to  the 
surface.     Smooth  the  upper  surface  before  ,it  hardens. 

Fig.  550. 


Gates  in  Watt's  flask. 

When  the  investing  material  is  hard,  warm  the  flask  slightly,  part  it, 
and  remove  the  wax.  From  a  small  tea-kettle  pour  a  stream  of  boiling 
water  in  the  mould  to  wash  out  any  wax  remaining  around  the  pins  or 
in  places  difficult  of  access.  The  position  of  the  gates  cut  in  the  lower 
half  of  the  investment  will  be  shown  by  ridges  in  the  upper  half.  By 
marking  a  slight  cut  at  each  side  of  the  ridge  and  making  a  groove  in 
place  of  the  ridge  the  gates  of  the  two  halves  will  correspond. 

Fasten  together  the  two  halves  of  the  flask  and  lute  the  joint  care- 
fully with  investing  material  to  prevent  escape  of  the  metal.  Dry  the 
flask  over  low  heat  an  hour  or  more  till  all  moisture  is  driven  out.  The 
presence  of  moisture  may  be  determined  by  holding  a  mirror  over  the 
gate.  If  the  mould  is  perfectly  dry,  no  steam  will  be  condensed  on  the 
glass.  Do  not  apply  heat  too  rapidly  or  steam  will  form  in  the  mould 
and  crack  it. 

Melt  the  metal  in  a  clean  iron  ladle  or  in  a  crucible,  being  careful  not 
to  overheat  it,  and  pour  it  in  the  mould  while  the  mould  is  still  hot.  If 
poured  in  a  cold  mould,  the  metal  does  not  take  so  sharp  an  impression, 


CAST-METAL  DENTURES.  473 

being  chilled  and  solidified  before  it  reaches  the  finer  parts  of  the  im- 
pression. The  nearer  the  temperature  of  the  mould  is  to  the  melting- 
point  of  the  alloy  the  finer  will  be  the  cast.  If  the  joint  of  the  flask  is 
well  luted,  no  metal  will  escape. 

After  the  flask  is  cold  it  may  be  opened,  the  denture  removed,  and 
the  surplus  parts  sawed  off.  These  may  be  laid  aside  for  future  use,  as 
remelting  will  not  injure  the  alloy  unless  the  temperature  has  been  car- 
ried too  high  and  some  of  the  component  parts  oxidized,  changing  the 
formula  of  the  alloy. 

The  denture  should  now  be  smoothed  with  tiles  and  sand-paper,  then 
polished  with  pumice-stone,  and  finally  with  chalk  or  rouge.  This  will 
require  less  time  in  proportion  to  the  pains  taken  in  smoothing  the  wax. 

Enough  metal  should  be  used  to  fill  the  mould  and  the  gates  full,  so 
that  the  weight  of  metal  at  the  top  will  force  the  lower  portion  into  all 
intricate  parts.  If  the  mould  is  not  full,  keep  it  hot  till  more  metal  can 
be  melted  and  poured  in. 

If,  after  the  mould  is  opened,  it  is  found  that  it  has  not  been  filled 
thoroughly,  it  should  be  closed,  fastened,  and  the  joint  luted,  then  heated 
to  the  melting-point  of  the  alloy.  Pour  in  more  metal  and  tap  the 
mould  gently  with  a  small  hammer  to  dislodge  any  air-bubbles  present 
-and  settle  the  metal  in  the  finer  parts. 

Repairs. — A  tooth  may  be  added  by  cutting  out  a  dovetailed  space 
for  the  pins,  waxing  it  in  and  investing  in  the  flask  in  about  the  same 
manner  that  a  vulcanite  denture  would  be  invested.  That  is,  imbed  the 
plate  in  the  lower  half  of  the  flask  and  cover  it,  all  but  the  wax  portion. 
Place  it  in  such  a  position  that  a  channel  can  be  cut  from  the  wax  to  the 
pouring  gate.  Complete  the  flasking  as  usual,  remove  the  wax,  dry  the 
whole,  melt  some  of  the  metal,  and  pour  it  in. 

Soldering-. — Solders  are  provided  by  difl^erent  manufacturers.  Make 
a  dovetailed  space  in  the  plate,  fit  and  wax  the  tooth  in  place  as  usual, 
then  imbed  an  investing  material,  leaving  the  wax  exposed.  Pemove 
the  wax,  dry  the  case,  apply  dilute  chloride  of  zinc  to  the  metallic  sur- 
face exposed,  place  a  piece  of  solder  in  position,  and  apply  the  heated 
soldering-iron  till  it  is  melted.  It  may  be  necessary  to  press  the  solder 
into  the  space  with  a  wad  of  paper.  Wood's  metal,  melting  at  180°  F., 
may  be  used  as  a  solder  in  such  a  case.  Investment  is  not  always  neces- 
sary, as  sometimes  a  tooth  or  block  may  be  held  in  place  with  the  fingers, 
protected  by  a  wad  of  paper,  while  the  solder  is  fused. 

A  tooth  may  be  added  or  attached  to  a  cast-metal  plate  wath  vulcanite 
by  roughening  the  place  of  attachment,  drilling  holes  in  the  plate  in 
different  directions,  and  countersinking  them  if  they  pass  through  the 
plate,  or  by  cutting  a  dovetailed  space.  The  plate  is  then  flasked,  and 
the  process  continued  as  in  repairing  a  vulcanite  plate. 

Vulcanite  Attachment. — To  avoid  weight  in  entire  superior  dentures, 
many  partial,  and  some  inferior  dentures,  it  is  better  to  cast  the  plate 
alone  and  attach  the  teeth  with  vulcanite.  In  such  a  case  make  a  thin 
wax-plate  of  the  exact  size  needed,  invest  it,  and  cast  a  plate  as  pre- 
viously described. 

Attachment  of  vulcanite  may  be  made  by  drilling  holes  in  the  plate 
and  countersinking  them  on  the  palatine  surface.  A  better  plan  is  given 
by  Dr.  Kingsley  :  In  the  wax-plate  on  the  ridge  set  several  small  gimp 


474     CAST  DENTURES  OF  ALUMINUM  AND  FUSIBLE  ALLOYS 

tacks,  imbedding  the  head  in  the  wax  and  letting  the  points  project  in 
different  directions.  When  the  case  is  invested  and  the  wax  removed, 
the  tacks  will  remain  in  the  investment,  and  should  be  pulled  out.  When 
the  plate  is  cast  the  tacks  will  be  represented  by  projections  of  the  metal 
base,  which  may  be  bent  in  the  form  of  loops. 

Fig.  551. 


Upper  cast  plate  for  vulcanite  attachment. 

Another  good  plan,  after  the  mould  of  a  plain  plate  is  made,  is  to 
make  holes  in  the  investment  with  a  small  drill  wherever  projections  on 
the  plate  are  needed. 

A  rim  may  be  made  on  a  plate  by  adding  a  wax  rim  to  the  wax-plate. 


Fig.  552. 


Lower  cast  plate  for  vulcanite  attachment. 


The  rim  and  plate  should  be  joined  for  at  least  one-sixteenth  of  an  inch 
from  the  edge  of  the  plate,  then  separated  slightly.  The  first  precaution 
is  to  allow  trimming  the  border  of  the  finished  plate  if  necessary.  An- 
other band  may  be  made  on  the  lingual  surface  of  the  wax-plate  with  a 


CASTING  ALUMINUM.  475 

strip  of  wax.  The  line  of  union  should  be  smoothed  and  the  wax  rim 
curved  to  conform  to  the  general  contour  of  the  plate.  On  a  lower 
plate  the  band  should  extend  around  both  labial  and  lingual  borders. 
These  bands  and  rims  will  be  reproduced  in  the  cast  metal  as  shown  in 
Figs.  551  and  552. 

The  cast  plate  can  be  used  for  taking  the  bite  and  mounting  the 
teeth  in  the  same  manner  as  a  wax  base-plate  or  a  swaged  plate  for  vul- 
canite attachment. 

Clasps. — As    these    cast    alloys    are    lacking    in    elasticity,    clasps 
should  be  made  of  clasp  gold  and  united  to  the  plate  in  casting  by  pro- 
viding:   suitable    attachments,  such    as  ^      ..„ 
pins  soldered  to  the  clasp  or  extensions 
which  may  enter  the  plate  a  third  or 
half    an   inch    (Fig.  553).      Where   a 
standard  clasp  can  be  used   the  stand- 
ard may  be  so  bent  as  to  extend  into 
the   plate.      These   clasps    should    be 
previously  fitted  in  the  mouth,  then  placed  on  the  teeth  of  the  cast  and 
secured  with  investing  material. 

Casting  Aluminum. 

On  account  of  the  low  specific  gravity  and  strength  of  aluminum 
many  attempts  have  been  made  to  make  cast  dentures  of  it,  but  the  very 
quality  which  made  it  desirable  in  one  respect  was  the  cause  of  failures  in 
casting.  It  is  so  light  that  it  will  not  of  its  own  weight  run  into  a  mould, 
at  least  not  into  an  intricate  one. 

The  first  successful  attempts  at  casting  were  made  by  Dr.  J.  B.  Bean 
of  Baltimore,  who  depended  on  the  weight  of  a  column  of  the  metal 
several  inches  high  to  force  the  lower  part  into  the  mould.  His  flask 
was  similar  to  those  used  for  other  cast  dentures,  but  was  provided  with 
a  detachable  clay  chimney  which  fitted  accurately  in  the  pouring  gate. 
The  flask  and  chimney  were  heated  separately,  then  joined,  and  enough 
melted  aluminum  poured  in  to  fill  the  mould  and  chimney.  The  weight 
of  molten  metal  in  the  chimney  was  sufficient  to  force  the  mould  full  and 
make  a  very  sharp  and  accurate  casting. 

Heretofore  the  chief  obstacle  to  the  use  of  dentures  of  aluminum  has 
been  its  deterioration  in  the  mouth.  Aluminum  of  commerce  was  con- 
taminated by  iron  or  other  metals  which  rendered  it  susceptible  to  chem- 
ical or  electrical  action,  such  action  being  often  confined  to  small  spots 
till  perforations  were  made. 

Aluminum  Cast  Dentures. — Dr.  C.  C.  Carroll  of  Meadville,  Pa., 
has  invented  a  process  of  casting  aluminum  under  pressure.  To  control 
shrinkage  he  has  alloyed  it  slightly  so  that  it  can  be  cast  directly  on  the 
teeth.  He  furnishes  the  following  formula  as  the  composition  of  his 
two  bases : 

Base  No.  1 :  Aluminum,  98  per  cent. ; 

Platinum,  "j 

Silver,         V    2 

Copper,     J 
Specific  gravity,  2.5;  fusing-point,  1300°  F. 
This  is  for  superior  dentures  and  must  be  cast  under  pressure. 


476     CAST  DENTURES  OF  ALUMINUM  AND  FUSIBLE  ALLOYS. 


Fig.  554. 


Base  No.  2  is  composed  of  aluminum,  tin,  copper,  and  silver ;  specific 
gravity,  7.5  ;  fusing-point,  700°  F.  This  is  intended  for  lower  dentures 
and  is  cast  without  pressure. 

To  cast  under  pressure  he  used  a  crucible  open  at  the  top  and  ter- 
minating in  a  nipple  at  the  bottom.  The  opening  in  the  nipple  con- 
nected with  the  inner  part  of  the  crucible  by  a  siphon-shaped  passage  in 

the  sides,  so  that  the  molten  metal  could  not 
run  out  by  gravity.  In  the  top  of  the  crucible 
was  fitted  a  plug  from  which  a  tube  led  to  a 
rubber  bulb.  By  pressure  on  the  bulb  the  air 
forced  the  molten  metal  through  the  nipple  at 
the  bottom. 

The  flask,  similar  to  Weston's  (Fig.  548), 
had  an  opening  in  the  upper  end  in  which  the 
nipple  of  the  crucible  fitted  tightly.  The  mould 
and  crucible  were  heated  separately  till  the 
aluminum  was  melted  and  the  flask  was  nearly 
red  hot.  The  crucible  was  then  placed  on  the 
flask  so  that  the  nipple  fitted  tightly.  The 
stopper  was  inserted  in  the  crucible,  and  the 
rubber  bulb  connected  with  it  squeezed  so  as 
to  force  the  aluminum  in  the  mould. 

While  cast  aluminum  is  not  as  tough  as 
swaged  aluminum,  yet  a  plate,  especially  a 
partial  one,  may  be  made  stronger,  because 
the  thickness  may  be  varied  according  to  the 
strain. 

Aluminum  plates  may  be  cast  directly  on 
the  teeth  or  plates  may  be  made  for  vulcanite 
attachment  (Fig.  551).  The  process  of  making 
the  base-plate  and  flasking  is  exactly  like  that 
described  for  other  cast-metal  plates,  except 
that  the  Avax  may  be  thicker  if  desired,  on  account  of  the  light  weight 
of  aluminum. 

Gates. — Three  round  channels  are  cut  in  the  mould,  one  from  the 
middle  of  the  posterior  border  to  the  pouring  gate,  and  one  from  each 
"  heel "  of  the  plate  to  the  edge  of  the  flask.  One  of  these  connects  with 
a  vent  hole. 

Carroll's  improved  flask  (Fig,  554)  has  a  projecting  gate-funnel, 
screw  cut  on  the  outside.  The  improved  crucible  screws  on  this,  so  as 
to  make  a  tight  joint.  The  crucible  cover  is  held  in  position  by  a  clamp 
with  a  handle  a  few  inches  long. 

After  flasking  and  removing  the  wax  "bolt  the  flask  firmly  together 
and  coat  the  thread  of  flask  with  soapstone.  Screw  the  retort  firmly  to 
the  flask.  Place  a  fine  copper  wire  in  the  vent,  then  lute  the  seam  of 
the  flask  and  where  retort  joins  the  flask,  also  around  the  bolts,  with  in- 
vesting material,  to  prevent  the  escape  of  air  or  metal  in  casting.  Test 
with  the  rubber  bulb  and  clamping  lever.  Soapstone  sprinkled  over  a 
suspected  leak  will  detect  it. 

"  Withdraw  the  wire  from  the  vent  and  test  again  to  see  that  only 
the  vent  is  open.     Place  the  flask  in  the  slot  of  the  burner,  turn  on  low 


CASTING  ALUMINUM.  477 

flame,  and  dry  out  thoroughly,  as  will  be  shown  if  no  moisture  appears 
on  the  surface  of  a  mirror  held  over  the  retort. 

"  When  the  piece  is  dry  place  the  flask  on  the  bottom  of  the  burner ; 
put  two  ingots  of  aluminum  base  No.  1  in  the  retort ;  place  the  hood 
over  it  and  turn  on  full  flame,  and  with  use  of  foot-bellows  attached  to 
air-tube  of  the  burner  proceed  to  melt  the  metal,  which  will  usually 
require  from  six  to  ten  minutes. 

"When  melted,  remove  the  hood,  turn  off  the  gas,  and  clamp  the 
retort  cover  in  place  with  clamping-tongs,  slipping  the  ring  over  handles  ; 
then,  with  the  rubber  bulb  pressed  gently  but  firmly,  force  the  melted 
metal  into  the  matrix  until  the  metal  is  forced  through  the  matrix  to  the 
vent."  "  Chill  the  metal  with  a  piece  of  wet  sponge  tied  to  a  stick  as 
soon  as  it  appears  at  the  vent.  Press  three  seconds  to  condense  the 
metal  under  pressure  in  the  matrix.  With  the  handles  of  the  clamping- 
tongs  unscrew  the  retort  from  the  flask  as  it  stands  in  the  burner,  and 
with  bulb  blow  out  all  excess  of  aluminum  from  the  retort." 

When  the  flask  is  cool  open  it,  cut  ofl"  surplus  parts  from  the  plate, 
trim  the  edges,  smooth  with  sand -paper  (fine),  and  polish  with  fine 
pumice-stone  and  chalk  or  rouge.  As  alumininii  is  much  harder  than 
the  "fusible  bases,"  much  more  care  should  be  taken — smoothing  the 
wax  model-plate. 

Clasps. — As  aluminum  has  much  more  strength  than  the  softer  plate 
alloys,  clasps  may  be  cast  about  the  teeth  by  making  proper  wax  models. 
A  better  plan,  however,  is  to  make  gold  clasps  and  connect  them  to  the 
plate  as  in  other  cast  metal  or  vulcanite  work.     (See  Fig.  553.) 

For  casting  a  plate  directly  on  the  teeth  the  same  precautions  should 
be  taken  as  those  described  on  p.  470.  The  teeth  should  be  spaced  so 
that  a  postal  card  will  pass  between  them  to  prevent  cracking  from  the 
slight  shrinkage  of  the  metal. 

After  investing  and  washing  out  the  wax,  "  make  a  thin  cream  of 
equal  parts  of  carbonate  of  magnesia  and  prepared  chalk  with  water,  and 
with  a  small  camel's-hair  pencil  cover  the  alveolo-labial  edge  of  the 
teeth  with  a  thin  coating  of  this  cream  to  prevent  the  metal  from  flow- 
ing over  this  edge  and  possibly  checking  the  teeth." 

"  If  the  gum  section  teeth  are  used,  grind  the  feather  edge  slightly 
bevelled,  leaving  the  labial  edge  of  the  gum  highest,  and  mount,  spacing 
slightly  by  placing  heavy  writing-paper  between  the  joints.  Before  in- 
vesting remove  the  paper  and  flow  between  the  joints  the  magnesia  and 
chalk  cream.  Then  invest  the  same  as  for  plain  teeth.  After  wash- 
ing out  the  wax  flow  a  thin  film  of  the  above  cream  along  the  bevelled 
edge  of  the  gum  and  proceed  to  cast  as  directed." 

Lo'wer  Dentures. — Carroll's  aluminum  alloy  for  lower  dentures  is 
lighter  and  more  rigid  than  the  plate  alloys  not  containing  aluminum,  but 
it  will  flow  of  its  own  weight  into  the  mould.  It  may  be  used  exactly 
like  the  other  alloys,  or  may  be  used  with  the  aluminum  outfit  as  follows  : 
After  the  teeth  are  arranged  as  desired  "  trim  and  wax  up  neatly,  and  as 
light  as  intended  to  be  when  finished  for  the  mouth.  Then  invest  the 
model  and  the  teeth  in  perforated  flask  and  proceed  as  directed  for  base 
No.  1  up  to  the  point  of  making  the  cast.  When  the  matrix  is  dry  and 
ready  to  make  the  cast,  place  two  ingots  of  base  No.  2  in  the  retort  with 
the  larger  opening.     Turn  on  flame  enough  to  melt  the  metal  in  eight 


478     CAST  DENTURES   OF  ALUMINUM  AND  FUSIBLE  ALLOYS. 

to  ten  minutes,  which  requires  not  over  half  the  flame  needed  for  base 
No,  1.  Stop  the  opening  with  an  old  plugger  to  prevent  the  metal 
escaping  as  it  melts.  When  all  is  melted  withdraw  the  stopper  and 
chill  the  metal  when  it  appears  at  the  vent, 

"  If  there  should  be  any  point  of  leakage  of  the  metal,  it  can  be 
stopped  at  once  by  touching  it  with  a  wet  cloth,  and  any  escaped  metal 
can  be  immediately  remelted  and  poured  into  the  matrix  without  pro- 
ducing any  flaw  or  imperfection  in  the  piece  to  be  cast.  Let  the  piece 
cool  slowly,  remove  from  the  flask,  and  finish  as  directed  for  base  No. 
1.     Never  use  the  same  retort  for  melting  base  No.  1  and  base  No.  2." 

The  aluminum  furnace  can  be  heated  with  either  gas  or  gasoline. 


CHAPTER   XV. 

VULCANIZED    RUBBER  AS  A  BASE    FOR  ARTIFICIAL 

DENTURES. 

By  Chaeles  J.  Essig,  M.  D.,  D.  D.  S.,  and  Warrington  W.  Evans, 

M.  D.,  D.  D.  S. 


Caoutchouc  (or  India-rubber)  is  the  thickened  milky  juice  of  several 
species  of  Ficus,  Euphorbia,  and  other  trees  growing  in  tropical  countries, 
and  is  essentially  a  mixture  of  several  hydrocarbons  isomeric  or  polymeric 
with  turpentine  oil.  When  pure  it  is  nearly  white,  the  dark  color  of 
commercial  caoutchouc  being  due  to  the  effects  of  smoke  and  other  im- 
purities. It  is  softened,  but  not  dissolved,  by  boiling  water :  it  is  also 
insoluble  in  alcohol.  It  dissolves  in  pure  ether,  chloroform,  rectified 
petroleum,  mineral  naphtha,  bisulphide  of  carbon,  benzole,  and  most  of 
the  oils,  both  fixed  and  volatile.  Dissolved  in  oil  of  turpentine,  it  forms 
a  viscid,  adhesive  mass  which  dries  very  imperfectly.  Caoutchouc  melts 
at  a  temperature  of  250°  F.,  but  little  above  the  boiling-point  of  water, 
but  does  not  again  resume  its  former  elastic  state.  By  destructive  dis- 
tillation it  yields  a  large  quantity  of  a  thin,  volatile,  oily  liquid,  having 
a  naphtha-like  odor,  called  caoutchin,  Ci^Hig,  which  dissolves  caoutchouc 
with  facility. 

The  caoutchouc  of  commerce  contains  a  small  quantity  of  albumin, 
derived  from  the  original  milky  liquid,  this  being  really  a  solution  of 
albumin  holding  in  suspension  about  30  per  cent,  of  caoutchouc,  which 
rises  to  the  surface  like  cream  when  the  juice  is  diluted  with  water  and 
allowed  to  stand,  becoming  coherent  and  elastic  when  exposed  to  air. 
The  specific  gravity  of  caoutchouc  is  0.93.  The  chief  uses  of  this  sub- 
stance depend  upon  its  physical  rather  than  its  chemical  properties,  its 
lightness  and  impermeability  to  water  adapting  it  for  the  fabrication  of 
many  articles  intended  for  the  exclusion  of  moisture,  while  its  remark- 
able elasticity  gives  rise  to  numerous  other  applications. 

Vulcanizable  caoutchouc  is  produced  by  incorporating  sulphur  with 
caoutchouc  in  proportions  varying  according  to  the  uses  for  which  it  is 
intended,  the  hardness  of  the  product  being  governed  by  the  amount  of 
the  indurating  agent  present. 

Hard  rubber  for  dental  purposes  (ebonite)  is  produced  by  exaggerating 
the  conditions  of  ordinary  vulcanization  or  increasing  the  proportion  of 
sulphur  added,  and  lengthening  the  period  during  which  it  is  allowed  to 
react  on  the  rubber.  The  sorts  of  rubber  best  suited  for  the  production 
of  ebonite  are  those  hard  and  fibrous  varieties  which  are  procured  in  the 
islands  of  the  Malayan  Archipelago.  To  Dr.  Thomas  W.  Evans  of  Paris, 
France,  is  undoubtedly  due  the  credit  of  having  made  the  first  dental 
plate  in  hard  rubber,  and  of  having  also  first  applied  steam  heat  for  the 

479 


480    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL   DENTURES. 

vulcanization  of  caoutchouc  in  chemical  combination  with  sulphur  and 
other  pigments  as  coloring  matter,  etc. :  this  was  in  1844  and  1845;  later 
on,  between  1848  and  1850,  Goodyear  provided  some  fine  specimens  of 
ebonite  work  which  demonstrated  the  industrial  value  of  the  material. 

There  is  some  difficulty  in  obtaining  accurate  formulas  for  compound- 
ing the  rubber  used  in  the  manufacture  of  dental  plates,  as  naturally  the 
manufacturers,  who  are  in  mercantile  competition  with  one  another,  are 
not  willing  to  publish  their  recipes.  The  formulse  which  seem  to  approx- 
imate the  compounds  are  those  given  by  Dr.  E.  Wildman,  as  follows : 

Dark  Brown.  Grayish  White. 

Caoutchouc 48  parts.     I  Caoutchouc 48  parts. 

Sulphur 24     "  vSulphur 24     " 

I  White  Oxide  of  Zinc 96     " 

Bed.  Black. 

Caoutchouc 48  parts. 

Sulphur 24     " 

Ivory-black  or  dee[)-black    ...  22     " 


Caoutchouc 48  parts. 

Sulphur 24     " 

Vermilion 36     " 


Dark  Pink.  Jet  Black. 


Caoutchouc 48  parts. 

Sulphur 24     " 

White  Oxide  of  Zinc 30     " 

Vermilion 10     " 


Caoutchouc 48  parts. 

Sulphur  .    .  24     " 

Ivory-black  or  Drop-black  ...  48     " 


Rubber  Dentures. 

It  is  important  that  the  model  used  in  the  construction  of  a  rubber 
denture  should  be  formed  of  the  hardest  variety  of  plaster,  so  as  to  enable 
it  to  sustain  without  danger  of  fracture  the  great  pressure  to  which  it  is 
subjected  after  packing,  and  while  the  two  parts  of  the  flask  are  being 
forced  together.  It  should  also  be  regarded  as  imperative  in  rubber  Avork 
that  the  surface  of  the  model  be  absolutely  free  from  minute  air-bubbles 
or  other  imperfections  incident  to  hasty  or  careless  mixing  of  the  plaster, 
improper  preparation  of  the  surface  of  the  impression,  etc.,  as  all  defects 
of  the  surface  of  the  plaster  model  will  be  found  clearly  defined  in  the 
rubber  plate  when  finished,  and  the  minute  points  or  prominences  so 
formed  act  as  irritants  to  the  delicate  tissues  upon  which  they  rest. 

A  slow-setting,  coarsely-ground  plaster  of  great  hardness  can  always 
be  obtained  at  the  establishments  where  plaster  ornaments  for  building 
purposes  are  manufactured,  and  is  much  better  suited,  both  for  the  for- 
mation of  the  model  and  for  flasking  the  denture,  than  the  grades  of 
plaster  usually  supplied  by  the  dental  depots. 

Every  detail  of  laboratory  work  should  be  done  intelligently  and 
with  care,  even  in  the  mixing  of  plaster — a  process  which  many  consider 
unimportant.  The  result  may  be  greatly  impaired,  although  the  material 
used  be  of  the  most  satisfactory  quality,  by  mixing  with  too  large  an 
amount  of  water,  and  neglecting  to  exclude  the  air  before  stirring  the 
plaster,  by  not  dropping  it  into  the  water  and  allowing  it  to  settle,  as  de- 
scribed   in  chapter  on  Models. 

The  model  should  be  trimmed  to  a  size  and  form  corresponding  with 
the  dimensions  of  the  flask.  The  next  step  is  to  arrange  the  vacuum 
chamber,  which  is  usually  formed  of  a  piece  of  "  chamber  metal  "  con- 
sisting; of  lead  with  a  coatinp;  of  tin  on  both  sides.     This  combination  is 


RUBBER  DENTURES.  481 

admirably  adapted  for  the  purpose  on  account  of  its  fiexibilty  :  tin  alone 
would  require  so  much  force  to  bring  it  into  close  contact  with  the  model 
that  damage  to  the  latter  might  result,  while,  on  the  other  hand,  lead 
alone,  while  possessing  softness  enough  to  enable  it  to  readily  take  the 
form  of  the  palatal  portion  of  the  mouth  without  much  pressure,  com- 
bines to  some  extent  with  the  sulphur  of  the  rubber,  and  thus  prevents 
perfect  vulcanization  at  the  point  of  contact.  The  shape  and  size  of  the 
chamber  should  conform  to  the  outline  and  dimensions  of  the  model ;  its 
position  should  be  posterior  to  the  rugae,  and  it  should  not  be  allowed  to 
include  to  any  considerable  extent  the  sloping  sides  of  the  ridge.  (See 
chapter  on  Models.) 

The  chamber  may  be  carved  in  the  impression,  and  some  operators 
prefer  this  method.  It  has  the  advantage  of  being  fixed,  and  therefore 
free  of  the  danger  of  becoming  accidentally  moved  out  of  its  correct 
position  when  the  two  parts  of  the  flask  are  brought  together. 

There  are  cases  occasionally  met  with  where  stronger  and  better 
atmospheric  adhesion  can  be  secured  without  the  vacuum  chamber.  In 
such  instances  the  whole  plate  may  be  given  somewhat  the  character  of 
a  vacuum  chamber  by  cutting  with  a  broad  Palmer  excavator  a  half- 
round  groove  entirely  around  the  plaster  model  a  little  above  the  line 
which  marks  the  extent  of  the  plate.  The  groove  will  be  represented  on 
the  vulcanite  denture  by  a  raised  line  of  about  the  thirty-second  of  an 
inch  in  width  and  somewhat  less  in  thickness.  This  raised  line  very 
soon  becomes  imbedded  in  the  tissues  and  prevents  the  ingress  of  air,  but 
care  must  be  exercised  in  finishing  the  piece  to  avoid  filing  away  any 
part  of  it,  otherwise  it  ceases  to  be  of  service. 

The  Base-plate. — There  are  numerous  materials  used  in  the  formation 
of  the  temporary  base-plates  for  rubber  and  celluloid  work  upon  which 
the  wax  articulation  is  taken.  In  the  early  days  of  rubber  work  the  tem- 
porary base-plate  was  invariably  made  of  sheet  gutta-percha  softened  by 
dipping  it  in  hot  water  and  pressed  to  the  plaster  model  with  the  thumb 
and  fingers,  and  then  trimmed  to  the  desired  dimensions :  it  was,  how- 
ever, objectionable  on  account  of  its  yielding  character,  the  consequent 
uncertainty  as  to  the  correctness  of  the  bite,  and  the  liability  to  impair 
the  condition  of  the  surface  of  the  plaster  model  while  making  it.  All 
forms  of  sheet  wax,  paraffin  and  wax,"  etc.  are  unreliable  as  materials  for 
the  formation  of  articulating  plates,  for  at  least  one  of  reasons  urged 
against  the  use  of  gutta-percha — extreme  pliability. 

The  most  reliable  of  the  materials  for  forming  temporary  or  articu- 
lating base-plates,  and  one  that  may  be  made  without  great  expenditure 
of  time,  is  the  tinned  lead  used  for  making  chambers.  This  metal 
can  be  obtained  of  any  desired  thickness,  and  by  making  one  zinc 
die  and  one  lead  counter-die  a  close-fitting  and  sufficiently  rigid  plate 
may  be  prepared  which  will  not  be  likely  to  yield  when  the  bite  is  taken 
in  the  mouth.  When  the  metallic  base-plate  is  used,  it  should  be  of  the 
thickness  of  No.  21  of  the  standard  gauge  :  this  will  require,  in  the  final 
waxing  up,  the  addition  of  a  sheet  of  extra-thin  wax  warmed  over  a 
spirit  lamp  and  pressed  to  close  contact  with  the  metal  plate  by  the 
thumb.  By  this  means  the  finished  denture  will  have  a  uniform  thick- 
ness of  about  No.  17  of  the  gauge.  Another  excellent  method  of  pre- 
paring temporary  base-plates  is  to  take  a  sheet  of  stout  pattern  metal 

31 


482    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


and  press  it  to  the  model  with  a  piece  of  erasing  rnbber  ;  a  sheet  of  wax 
is  then  warmed  and  pressed  to  the  metal ;  and,  finally,  another  layer 
of  pattern  tin  is  pressed  to  the  wax  :  this  afPords  a  plate  composed  of 
two  thicknesses  of  pattern  tin  with  a  sheet  of  wax  between  them.  If  the 
latter  is  of  the  extra-thin  variety,  the  combination  will  afford  a  plate  of 
the  proper  thickness,  No.  17,  and  the  plate  will  be  fonnd  to  be  nearly  as 
rigid  as  the  one  of  chamber  metal. 

When  sheet  wax  or  paraffin  and  wax  are  used  for  a  base-plate,  the 
plate  can  be  strengthened  by  a  piece  of  iron  or  brass  wire  of  not  less 
thickness  than  No.  15  or  No.  16  of  the  standard  American  gauge,  bent 
to  fit  the  ridge  of  the  base-plate  and  securely  waxed  to  it.  This  wire  is 
indispensable  in  lower  base-plates  of  wax. 

Taking-  the  Articulation. — This  is  an  operation  which  admits  of  a 
much  wider  scope  in  rubber  work  in  the  restoration  of  the  natural  ex- 
pression, which  is  always  more  or  less  changed  by  the  loss  of  the  natural 
organs,  than  was  possible  when  the  prosthetist  was  restricted  to  the  gold 
or  silver  denture.  Paraffin  and  wax  is  preferable  for  articulations  on 
account  of  the  proximity  of  color  to  the  natural  teeth,  an  ordinary  cake  of 
the  material  softened  over  the  flame  of  a  spirit-lamp,  and  doubled  and 
rolled  upon  itself  until  it  assumes  a  cylindrical  shape  of  sufficient  length  to 
occupy  the  greater  part  of  the  alveolar  ridge,  and  to  receive  impressions 
of  all  the  antagonizing  natural  teeth,  if  any  remain.  While  still  quite 
plastic  it  is  moulded  with  the  thumb  and  fingers  to  near  the  height  and 
fulness  required  by  the  particular  case,  after  which  considerable  time 
may  be  spent  in  trimming  the  wax  away  at  some  points  and  making 
additions  to  others  until  a  quite  natural  expression  of  the  mouth  has 
been  obtained. 

This  part  of  the  construction  of  an  artificial  denture  is  purely  artistic, 
and  there  is  but  scant  basis  for  the  formulation  of  rules  which  shall  guide 
the  student  with  any  degree  of  certainty  in  the  restoration  of  the  correct 
facial  expression.     With  exactly  the  same  materials  two  operators  will 


Fig.  555. 


Fig.  556. 


Showing  plumpers  for  restoring  expression. 


Antagonizing  model,  partial  upper  denture. 


obtain  widely  different  results  :  the  denture  prepared  by  one  will  blend  so 
harmoniously  with  the  face  as  to  become,  as  it  should  be,  an  inconspicu- 
ous feature,  suggestive  of  nothing  artificial,  while  the  other  will  be 
entirely  incongruous  in  effect. 


RUBBER  DENTURES. 


483 


There  are  four  important  points  in  the  arrangement  of  the  articulat- 


ing wax  which  demand  particular  attention.  These  are, 
first,  the  correct  length  ;  second,  proper  fulness  ;  third,  tlie 
right  curve;  fourth,  the  filling  up  of  depressions  in  the 
lips  or  cheeks  incident  to  the  loss  of  the  natural  teeth. 
A  defect  in  either  of  these  directions  will  be  sure  to  im- 
part to  the  mouth  an  unnatural  appearance.  The  ar- 
ticulating wax  should  be  recognized  as  a  reliable  guide 
for  the  subsequent  fitting  and  arranging  of  the  porcelain 
teeth,  and,  having  been  completed  in  a  satisfactory  manner, 
it  should  be  closely  followed. 

The  statement  is  often  made  that  with  the  loss  of  the 
cuspid  teeth  permanent  changes  occur  in  the  facial  ex- 
pression which  cannot  be  entirely  restored ;  but  the 
author  has  found  that  in  rubber  dentures  the  depression 
caused  by  the  loss  of  the  teeth,  as  well  as  the  changes 
which  occur  in  the  cheeks  from  similar  causes,  may  be 
entirely  restored  by  properly  arranged  prominences  of 
the  rubber  rim,  as  shown  in  Fig.  555. 

The  articulating  or  antagonizing  model  should  be 
made  upon  the  cast,  as  shown  by  Fig.  555.  The  cut 
exhibits  the  arrangement  for  obtaining  the  bite  of  a  par- 
tial denture,  but,  as  the  idea  is  precisely  the  same  in 
entire  upper  or  lower  dentures,  it  will  answer  to  illustrate 
the  relation  of  the  antagonizing  model  to  the  cast.  In 
making  the  antagonizing  model  for  an  entire  rubber 
denture  the  upper  and  lower  waxes  are  to  be  tempo- 
rarilv  united  in  their  correct  relation  to  each  other  by  hot 
wax  applied  at  two  or  three  points  by  means  of  a  spatula 
(Fig.  557)  ;  they  are  detached  from  their  respective  models, 
and  the  latter  are  cut  down  to  the  dimensions  required 
for  their  reception  in  the  vulcanite  flask.  They  are  then 
each  given  a  partial  coat'of  sandarac  varnish  on  their  base 

Fig.  558. 


Fig.  55 


sides  to  prevent  too  great  adhesion  to  the  plaster  articulator 
and  to  ensure  their  safe  separation  from  it  when  the  fitting 
and  arranging  of  the  teeth  are  finished  :  to  accomplish 
the  separation   it  is  only  necessary   to   introduce  a  knife-blade   at  the 


484     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 

points  indicated  by  A,  A,  Fig.  558,  and  pry  them  gently  apart. 
Plaster  antagonizing  models  are  more  convenient  to  handle  than  are 
any  of  the  metallic  articulators  supplied  by  the  dental  depots.  Being 
in  two  unattached  parts,  one  section  may  be  laid  aside,  instead  of 
dangling  by  a  hinge,  while  the  teeth  are  being  tried  in  place.  The 
articulation,  properly  so  called,  is  taken  in  the  mouth,  the  mouth  being 
the  true  articulator.  The  antagonizing  model  merely  fixes  the  correct 
relation  of  the  lower  to  the  upper  ridge.  It  is  stated  that  the  func- 
tion of  the  metallic  articulator  is  to  enable  the  workman  to  change  the 
bite  by  either  shortening  or  lengthening  if  he  deems  such  modification 
desirable.  A  change  in  the  articulator  nearly  always  impairs  the  accuracy 
of  the  relation  of  the  dentures,  because  with  the  exception  of  the  instru- 
ments of  Bonwill  and  of  Walker  the  forms  of  these  mechanical  fixtures 
are  not  anatomically  correct,  and  therefore,  while  they  may  be  employed 
merely  to  fix  the  relation  of  the  inferior  to  the  superior  teeth,  they  can- 
not be  relied  upon  as  a  means  of  changing  the  bite. 

Teeth  used  in  rubber  work  are  especially  designed  for  that  purpose, 
and  are  made  in  the  form  of  sectional  blocks,  single  gum,  and  plain 
teeth.  Objections  to  the  use  of  the  former  consist  in  the  difficulty  fre- 
quently met  with  in  adapting  them  to  the  curve  of  the  alveolar  ridge 
and  in  their  limited  range  in  the  imitation  of  irregularities.  On  the  other 
hand,  the  gums  of  sectional  rubber  block  teeth  may  be  made  to  imi- 
tate nature  more  closely  than  is  possible  with  any  of  the  colored 
rubbers  now  in  use  for  the  purpose.  Single  gum  teeth  for  rubber  work 
are  practically  obsolete  for  the  construction  of  entire  dentures,  on  ac- 
count of  the  number  of  joints  necessary  in  fitting  them  together,  the  lia- 
bility of  the  latter  to  become  discolored  by  the  rubber,  the  labor  of  fit- 
ting them  together,  and  the  difficulty  of  imitating  irregularities  of 
position. 

The  most  artistic  effects  are  obtained  wnth  plain  teeth  :  they  are  much 
easier  to  manipulate,  less  liable  to  the  danger  of  breakage  in  packing, 
and  during  subsequent  operations,  and  are  almost  entirely  free  from  the 
vexatious  shrinkage  of  the  rubber  from  around  the  teeth  so  often 
observed  in  sectional  blocks. 

By  the  use  of  single  plain  teeth  the  operator  has  abundant  oppor- 
tunity for  the  imitation  of  the  irregularities  observed  in  natural  dentures, 
and  time  and  labor  are  saved  through  the  facility  with  which  they  may  be 
made  to  conform  to  the  alveolar  ridge.       Fig.  560  to  represent  some  ex- 
cellent samples  of  plain  rubber  teeth  that 
Fig.  559.  will  be  found  available  in  a  majority  of 

cases. 

If  the  gums  are  formed  of  pink  rub- 
ber, and  modelled  so  as  to  give  the  proper 
fulness  to  the  lip  and  to  imitate  the  irreg- 
ularities of  surface  of  the  natural  gums, 

^_^       the  effect  will  not  be  bad.     It  is  always 

'^^i^^^^t^.         "[i^^^t  way.       better  to  keep  the  pink  rubber,  which  is 

not  a  very  close  imitation  in  point  of 
color  to  the  natural  gum-tissue,  from  being  visible  in  laughing  or  talk- 
ing. The  artistic  shaping  of  the  gums,  however,  will  greatly  lessen  the 
artificial  appearance  of  the  denture. 


RUBBER  DENTURES. 

Fig.  560. 


485 


486     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 


In  the  fitting  of  sectional  blocks  or  single  gum  teeth — and  the  use 
of  the  latter  is  sometimes  necessary  in  partial  cases — cer-       ^ 
tain  precautions  are  requisite  in  the  preliminary  stages  of     ^      '  X.' 
Fig.  561.  ^^^  operation  to  prevent  the     \      lf% 

joints  from  becoming  discol-  |  f  |] 
ored  by  the  ingress  of  the  "'  '^  -' 
rubber  in  packing. 

Discoloration  of  the  joints 
is  due — First,  to  imperfect 
fitting  of  one  gum  section  to 
the  other ;  second,  to  want 
of  cleanliness ;  third,  to  an 
over-abundance  of  rubber  in 
the  flask  in  packing  •  fourth, 
to  an  inferior  quality  of  plas- 
ter, which  is  liable  to  yield 
when  the  flask  is  being  forced 
together.  In  fitting  sectional 
blocks  or  single  gum  teeth 
care  should  be  taken  in  joint- 
ing the  gums  to  have  the 
surfaces  that  come  in  contact 
so  ground  that  they  will  fit 
perfectly  and  not  form  a 
V-shaped  space  (Fig.  559) ; 
and  in  fastening  the  finished 
blocks  or  gum  teeth  to  the 
plate  not  a  particle  of  the  wax 
or  cement  used  for  tlie  pur- 
pose should  be  allowed  to 
run  into  the  joints,  and  when, 
all  the  teeth  are  in  position, 
and  before  the  final  "  waxing 
up"  is  begun,  fine  plaster 
mixed  with  water  should  be 
forced  into  the  joints,  so  as 
to  fill  the  slightest  crevice 
and  effectually  exclude  the 
melted  wax,  which  is  some- 
what freely  applied  with  the 
spatula  in  giving  the  finish- 
ing touches  to  the  waxing 
process.  The  plaster  may 
be  applied  to  the  inside  of 
the  joints,  and  if  mixed  thin 
it  will  be  drawn  by  capillary 
force  entirely  into  any  space,  I  |  | 
no  matter  how  minute  it  may  \ 
be.  "        ' 

Forming-  the  Denture  in        '         " 
"Wax. — Having  secured  the  teeth  in  position,  wax  is  liberally  dropped 


RUBBER  DENTURES. 


487 


under  them  if  gum  teeth,  and  quite  around  them  if  plain  teeth,  being 
careful  to  avoid  allowing  any  to  drop  on  the  palatal  portion  of  the  plate. 
When  plain  teeth  are  used,  the  wax  is  to  be  carved,  as  soon  as  sufficiently- 
cool,  around  the  necks  inside  and  out  with  suitable  tools  :  those  shown 
in  Figs.  561,  562,  with  accompanying  burner  (Fig.  563),  will  be  found 
very  convenient  for  the  purpose. 

The  front  should  be  carved  to  exactly  represent  the  gums  as  they 
appear  in  nature  and  as  the  piece  should  be  when  finished.  The  plate, 
previously  formed  of  wax  or  other  suitable  material,  should  be  of  a 
uniform  thickness  of  about  No.  17  of  the  standard  American  gauge, 
so  that  the  rugse  and  other  irregularities  of  the  palatal  surface  of  the 
mouth  may  be  observed.  There  is  hardly  room  for  doubt  that  the 
rugse  play  an  important  part  in  mastication  in  assisting  the  tongue 
to  change  the  bolus  of  food  from  one  part  of 
the  mouth  to  another,  and  as  aids  in  enuncia- 
tion and  deglutition.  It  seems,  therefore,  rea- 
sonable that  a  denture  so  arranged  will  feel 
less  foreign  to  the  patient  than  do  those  with 
perfectly  flat  surfaces  wherein  no  attempt  has 
been  made  to  imitate  the  palatal  configura- 
tion of  the  human  mouth.  

The  waxed  piece  should  be  regarded  as  a  pat- 
tern in  wax  from  which  a  matrix  is  to  be  obtained  for  the  purpose  of 
forming  the  permanent  rubber  denture ;  and  it  should  be  remembered 
that  the  labor  of  finishing  the  vulcanized  piece  Avill  depend  upon  the  per- 
fection to  which  the  modelling  of  the  wax  pattern  is  carried.  The  ope- 
rator will  usually  find  that  time  and  labor  are  saved  by  so  shaping  the 
wax  pattern  that  little  or  no  scraping,  filing,  or  polishing  is  needed  to 

Fig.  564. 


Fig.  563. 


the  vulcanized  piece.  When  the  carving  of  the  wax  is  satisfactorily 
finished  a  few  gentle  puflFs  of  a  mouth  blowpipe  will  flow  the  wax  and 
produce  a  perfectly  smooth  surface  when  it  is  ready  for  the  flask.  A 
sheet  of  No.  60  tin-foil  should  be  very  carefully  burnished  over  the  wax 


488     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


plate,  both  on  the  palatal  portion  and  that  part  representing  the  gums. 
Fig.  564  shows  a  set  with  the  gum  portion  entirely  covered  with  tin- 
foil:  the  stippling  observed  on  the  surface  is  done  by  means  of  a  blunt 
pointed  instrument  indenting  the  tin,  care  being  taken  to  merely  indent, 
but  not  punctuT-e,  the  tin. 

The  foil  should  be  cut  to  the  proper  dimensions  and  carefully  brought 
in  contact  with  the  wax,  at  first  with  a  piece  of  soft  rubber,  such  as  is 
used  for  erasing  pencil-marks,  to  avoid  folds,  and  then  with  the  ivory  or 
agate  burnisher  which  accompanies  the  set  of  carvers  (Fig.  561). 

Care  must,  of  course,  be  exercised  in  investing  or  packing  the  piece 
to  avoid  disturbing  the  tin-foil.  The  tin-foil  on  the  palatal  surface,  if 
the  operator  prefer,  may  be  put  on  after  the  denture  has  been  invested 
in  the  lower  section  of  the  flask. 

Flasks  for  the  Vulcanizing-  Process. — There  are  many  good  flasks 
from  which  to  select.  They  are  usually  made  of  iron  or  brass,  and  are  di- 
vided into  two  sections  with  detachable  top-  and  bottom-pieces,  as  shown 

in  the  illustration  of  the  "Star 
reversible  flask"  (Fig.  565). 

Fig.  566  shows  the  "Whitney 
slot  flask."  This  flask  has  been 
extensively  used  for  many  years : 
it  is  not,  however,  reversible, 
and  the  bottom-piece  not  being 
removable,  it  has  been  to  some 
extent  superseded  by  the  Star  re- 
versible flask  on  account  of  the 
greater  convenience  of  the  latter. 
Figs.  567  to  572  show  the  dif- 
ferent parts  of  the  Griswold  flask, 
an  appliance  of  somewhat  recent 
invention.    Those  who  have  used 

Fig.  566. 


Fig.  565. 


The  improved  Star  reversible  brass  flask. 


Whitney  slot  flask. 


this  flask  report  that  it  is  convenient,  strong,  and  capacious.  It  is  made 
of  three-thirty-seconds  of  an  inch  rolled  brass  of  uniform  thickness,  the 
base  and  top  being  shaped  by  heavy  pressure  over  steel  dies,  which  leaves 
the  flask  polished  inside  and  out.  The  uniformity  of  thickness,  fineness 
of  form,  and  flawless  metal  give  it  superiority  over  flasks  of  cast  metal 
and  ensures  great  strength  and  capacity,  while  at  the  same  time  it  will 
enter  the  smallest  vulcanizer.  This  flask  is  especially  adapted  to  the 
"  Griswold  method,"  briefly  described  as  follows  :  "  Put  the  waxed-up 


RUBBER  DENTURES. 


489 


model  in  base  B  (Fig.  567),  level  the  plaster  to  the  gum  and  palate  edge 
line  as  shown  and  varnish  the  surface.  Lock  the  centre  C  (Fig.  568)  on 
the  base  B  by  turning  the  coned  nut  E,  E  (Fig.  567).  Soap-lather  the 
varnished  surface  to  the  gum  and  palate  edge  line,  pour  and  level  the 


Fig.  567. 


Fig.  568. 


plaster  to  cover  the  ends  of  the  teeth,  and  slope  the  plaster  up  from  the 
palate  edge  to  the  centre  C(rear  edge,  Fig.  568).  Soap-lather  the  var- 
nished plaster  and  waxed-up  surfaces,  lock  the  top  T  on  the  centre  C,  as 
in  Fig.  569,  and  pour  plaster  through  the  hole  in  the  top,  jarring  the 
flask  to  ensure  its  being  filled,  and  turn  the  half  disk  to  close  the  top. 


490    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


After  the  plaster  lias  set  thoroughly,  unlock,  apply  heat,  and  separate 
the  flask,  and  cut  grooves  for  surplus  rubber,  as  shown  in  1  and  2  in  the 
top  T  (Fig.  569)  and  3  and  4  in  the  base  B  (Fig.  567).  Remove  the 
wax  with  boiling  water,  lock  T  on  C  (Fig.  568),  pack  pink  rubber  neatly 
for  labial  and  buccal  gum  surfaces,  press  T  and  C  on  JB,  and  lock  them 
together,  as  shown  in  Fig.  571.  The  top  of  the  flask  should  not  be  re- 
moved nor  grooves  1  and  2  cut  until  after  the  wax  has  been  removed, 
the  pink  rubber  packed,  and  the  base  locked  to  the  centre,  when  T  (Fig. 
569)  may  be  separated  from  C,  B,  and  the  red  or  black  rubber  packed 
under  the  teeth  and  over  their  backs  and  into  the  palatal  part  of  the 
matrix  (Fig.  571).  A  solution  of  soap  is  then  applied  to  the  palatal  part 
of  the  top  J'(Fig.  570),  which  is  placed  on  C  (Fig.  569),  and  closed  under 
the  press  and  locked  as  in  Fig.  571.  If  too  much  rubber  has  been  packed 
to  permit  of  closing,  the  soap  solution  used  will  prevent  it  from  adhering 
to  the  plaster,  and  the  section  T  may  be  safely  separated  from  (J  to  re- 
move the  excess  of  rubber :  the  flask  may  be  closed,  pressed,  and  locked 
for  vulcanizing.  The  parts  of  this  flask  are  accurately  interchangeable, 
and  by  locking  the  centre  C  on  the  base  B  a  deep  base  is  formed  for 
flasking  partial  cases  in  the  way  shown  in  Fig.  570,  so  that  the  artificial 
teeth  are  not  separated  from  between  the  (natural)  plaster  teeth  and  cast 
at  the  risk  of  breaking  the  plaster  fracturing  or  displacing  the  artificial 
teeth,  but  by  packing  and  pressing  the  rubber  from  behind,  and  carefully 
pressing  and  locking  the  top  T,  Fig.  569,  on  C,  Fig.  568,  a  partial  den- 
ture may  be  moulded  in  which  neither  articulation  or  adjustment  are 
disturbed." 

There  is  a  class  of  partial  dentures  constructed  to  replace  the  central 
and  lateral  incisors  in  young  subjects  whose  front  teeth  have  been  lost 
through  neglect  or  accident.  In  such  cases  it  is  often  desirable  to  use 
sectional  blocks  of  two  teeth  each,  and  to  fit  the  gums  directly  upon  the 
plaster,  so  that  no  rim  of  rubber  may  be  seen  in  the  finished  piece.  In 
such  cases  the  flasking  must  be  done  in  a  way  to  allow  the  blocks  to 
remain  on  the  model  and  not  be  separated  from  between  the  plaster 
cuspids,  otherwise  the  porcelain  gums  are  very  liable  to  fracture.  The 
"  Griswold  flask  "  seems  to  be  admirably  adapted  to  cases  of  this  kind. 


Fig.  573. 


Fig.  574. 


Whitney  flask  (new  style). 


Whitney  flask  (deep). 


XIH- 


Figs.  573  to  576  represent  a  few  of  the  plainer  forms  of  flask,  some 
of  which  have  been  used  with  satisfaction  for  many  years.  The  cuts 
give  a  good  idea  of  their  appearance  and  construction.  Fig.  575  is 
the  ordinary  Whitney  flask,  with  extra  long  bolts  to  accommodate  spiral 


RUBBER  DENTURES. 


491 


springs,  the  purpose  being  to  close  the  flask  while  it  is  in  the  vulcanizer 
by  gentle  and  equable  pressure.  This  procedure  is,  however,  not  recom- 
mended, as  the  parts  of  the  flask  should  always  be  quite  together  before 
it  is  placed  in  the  vulcanizer. 

Fig.  575  represents  the  round  "  Hayes  flask,"  of  somewhat  greater 
capacity  than  the  others,  and  very  convenient  for  flashing  unusually 
large  dentures. 


Fig.  575. 


Fig.  576. 


Hayes  flask.    Size,  2%  X  314  X  Ws- 

Fig.  577  is  a  flask  of  recent  invention  designed  to  avoid  the  annoy- 
ance caused  by  the  stripping  of  the  thread  on  the  bolts.  It  consists 
of  a  flask  and  press  combined  :  the  press  as  seen  in  the  cut  remains 
in  situ  during  vulcanizing.  It  has  been  further  improved  by  the  substi- 
tution of  three  screws  set  in  triangle,  instead  of  the  single  (central  screw. 
When  the  guide  bars  of  vulcanizing  flasks  become  deformed  so  that 
they  no  longer  serve  as  true  guides,  the  flask  should  be  discarded. 


Flasking. — The  "  waxed-up  "  model  should  be  carefully  trimmed, 
and  saturated  with  cold  water  to  prevent  it  from  absorbing  the  water 
from  the  freshly-mixed  plaster :  the  model  should  be  tried  in  the  empty 
flask  to  see  that  it  is  not  too  high  or  wide  to  be  easily  received  by  the 
latter.  Plaster  should  then  be  mixed  to  saturation  with  water  and 
poured  into  the  lower  half  of  the  flask  marked  B  (Fig.  578),  and  the 
model  set  into  it.  The  practice  of  setting  the  model  in  the  flask  and 
then  pouring  the  plaster  in  should  be  avoided,  as  there  is  always  doubt 
about  the  plaster  running  under  the  model ;  and,  unless  the  latter  is 
completely  bedded  in  the  plaster,  it  will  invariably  break  when  pressure 
is  brought  to  bear  upon  it  in  packing.  The  model  should  be  allowed  to 
stand  as  high  as  the  case  will  admit  without  the  teeth  touching  the  top. 


492     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


presuming,  of  course,  that  the  case  being  flasked  is  an  ordinary  full  den- 
ture, the  object  being  to  bring  the  line  of  separation  ^  to  the  lowest 
part  of  the  rim.     When  the  plaster  in  B  has  set,  it  is  to  be 
levelled  with  the  knife  and  given  a  coating  of  shellac  or      Fig.  579. 
sandarac  varnish,  and  then  oiled  or  soaped  as  the  operator 
prefers.     The  other  half  of  the  flask,  A,  is  placed  in  posi- 
tion, the  teeth  and  all  surfaces  wet  to  facilitate  the  flowing 
of  the  plaster,  which  is  then  carefully  poured  in  the  second 
section,  care  being  taken  to  avoid  air-bubbles  and  to  work 
the  plaster  well  against  and  between  the  teeth.     The  plas- 
ter should  be  allowed  to  fully  harden  before  any  attempt  is 
made  to  separate  the  two  parts  of  the  flask,  and  this  must 
not  be  done  until  the  flask  has  been  previously  heated  in 


Fig.  578. 


.^^  h 


boiling  water  for  the  purpose  of  softening  the  wax,  so  that 
no  resistance  will  be  met  with  in  parting  the  two  halves 
of  the  flask  A  and  B,  and  that  the  tin-foil  covering  to  the 
gums  and  palatal  portion  of  the  denture  will  not  be  dis- 
turbed. 

The  next  step  is  to  clear  the  case  completely  of  wax. 
If  any  of  the  latter  is  allowed  to  remain  in  the  matrix  or 
around  the  pins,  it  combines  with  the  rubber  and  greatly 
impairs  its  strength  and  toughness ;  it  is  therefore  neces- 
sary that  the  last  trace  of  it  be  removed.  This  is  most 
effectually  done  by  pouring  a  stream  of  boiling  water 
from  the  spout  of  an  ordinary  tea-kettle  into  the  flask 
and  over  the  teeth  and  wherever  a  trace  of  wax  is  visi- 
ble. The  flask  should  then  be  allowed  to  dry  for  a  few 
minutes.  To  ensure  absolute  freedom  from  wax  and  the 
danger  of  shrinkage  of  the  rubber  from  the  teeth — a  condi- 
tion often  due  to  failure  to  remove  every  particle  of  wax — 
the  teeth  and  pins  should  be  washed  with  strong  alcohol 
applied  with  a  camel's-hair  pencil. 

The  Vents. — Fig.  579  shows  a  very  convenient  bench-knife  for  the 
cutting  of  vents,  suggested  by  Prof.  N.  S.  HofF  of  Ann  Arbor  (Michigan 
University).  It  is  made  of  one  piece  of  steel,  strong  and  well  tempered. 
One  end  is  tapered   and  thinned  for  removing  plaster  impressions  from 


RUBBER  DENTURES. 


493 


casts  and  for  the  cutting  of  vents.  The  handle  of  the  knife  is  of 
akiminum,  and  is  therefore  light  and  agreeable  to  the  hand.  The 
vents  should  be  free,  and  sufficient  in  number  and  depth  to  readily 
admit  of  the  escape  of  surplus  rubber.  The  usual  manner  of  arranging 
them  is  to  cut  grooves  of  about  one-eighth  of  an  inch  in  depth  and 
about  three-sixteenths  of  an  inch  apart,  running  out  from  the  model  to 
a  somewhat  deeper  and  broader  groove  cut  entirely  around  the  model, 
as  shown  in  Fig.  580. 

Another  and  perhaps  better  method  is  shown  in  Fig.  578,  where 
it  will  be  seen  that  the  plaster  in  A  has  been  trimmed  away  from  the 
edge  of  the  rim  E  of  the  denture  to  the  border  of  the  flask,  deepening 
out  toward  the  latter,  F,  to  nearly  one-eighth  of  an  inch  entirely  around 
the  model,  as  shown  in  the  sectional  view  of  the  invested  case.  By  this 
means  sufficient  pressure  is  retained  on  the  case  until  the  soft  rubber 
has  found  its  way  into  all  the  interstices  of  the  teeth  and  plate,  at  the 

Fig.  580. 


same  time  leaving  ample  gateway  for  the  passage  of  all  the  surplus 
rubber,  without  the  necessity  for  the  application  of  much  force,  which 
might  damage  the  model  and  strain  the  flask  or  force  the  rubber  into 
the  joints  should  gum  teeth  be  used.  When  this  method  is  used  the 
two  parts  of  the  flask  selected  should  fit  each  other  perfectly  and  be 
in  complete  contact ;  otherwise  the  force  required  to  press  them  to- 
gether so  as  to  distribute  the  rubber  over  all  parts  of  the  matrix  may 
fall  upon  the  teeth  and  model  and  cause  fracture  of  one  or  both. 

In    cases  where  there   are  well-marked    undercuts  with    projecting 


494    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


Fig.  581. 


alveolus  in  front  the  Campbell   or  Seabury  oblique  sliding  guide-pin 
flasks  should  be  used  (Fig.  581). 

In  flasking  a  case  in  which  the  model  has  a  deep  undercut  in  front 

the  success  of  the  subsequent  details 
of  the  work  and  the  safety  of  the  den- 
ture will  depend  very  much  upon  the 
line  of  division  between  the  two  parts 
of  the  flask.  Keference  to  Fig.  582  will 
show  such  a  case  correctly  invested^ 
^immW      iiiiilih  .  ?h^  Pj^«*^^  "^  the  lower  section  cover- 

m  IIMiililffffiiiiy  ^"^         ^^^^  "^^^       withm  hall  a  line 

•  'liflRiiilHV  *^^    ^^^   porcelain   gums.     It  will   be 

^       •  .  '"iHiiBKB^  seen  readily  that  if  the  line  of  division 

had  been  made  at  the  extreme  upper 
edge  of  the  rim,  there  would  be  danger 
of  breaking  off  the  projecting  portion  of  the  model  in  front  on  the 
separation  of  the  flask. 

Fig.  582. 


The  Seabury  dental  flask. 


Fig.  583. 


Another  method  is  represented  in  Fig.  583  :  it  consists  in  trimming 
the  model  so  that  the  axis  of  the  undercut  will 
assume  as  nearly  as  possible  a  perpendicular  posi- 
tion in  the  flask.  In  all  such  cases  the  flask  should 
be  warmed  in  boiling  water  to  thoroughly  soften 
the  wax  before  any  attempt  to  separate  the  flask 
is  made. 

Should  the  undercut  or  projecting  portion 
of  the  plaster  model  become  broken,  the  success 
of  the  case  is  seriously  imperilled ;  yet  even 
such  an  accident  may  be  repaired  and  the  ope- 
ration successfully  completed.  The  wax  is  thor- 
oughly washed  from  the  model  with  boiling 
water ;  the  flask  is  then  allowed  to  dry  for  half  an  hour,  when  the 
broken  piece  may  be  fastened  to  the  model  by  means  of  gum-tragacanth 
paste,  and  then  reinforced  by  two  thicknesses  of  tin-foil  made  to  adhere 
by  means  of  the  tragacanth.  Of  course  in  such  cases  the  subsequent 
packing  must  be  done  with  unusual  care  :  rubber  cut  in  thin  strips  and 
warmed  must  be  packed  in  that  portion  of  the  matrix  representing  the 
rim,  as  shown  in  Fig.  582,  so  that  the  broken  piece  may  receive  support 
from  below.     A  very  considerable  surplus  of  rubber  must  be  avoided, 


RUBBER  DENTURES. 


495 


and  when  the  flask  is  quite  together  it  must  be  separated  and  the  broken 
piece  examined  to  ascertain  whether  it  has  been  forced  from  its  place 
while  the  rubber  was  under  pressure.  If  any  change  be  observed,  the 
piece  can  be  readjusted,  and  by  a  small  addition  of  rubber  outside  it  may 
be  held  in  correct  position  until  after  vulcanizing. 

In  cases  where  sectional  blocks  or  single  gum  teeth  are  fitted  to  rest 
directly  upon  the  natural  gums  in  order  to  avoid  unnecessary  fulness, 
the  division  of  the  two  parts  of  the  plaster  investment  should  be  at  the 
cutting  edges  of  the  teeth.  By  this  means  the  teeth  are  securely  fast- 
ened in  their  proper  relation  to  the  model  in  the  lower  section  of  the 
flask  (Fig.  584). 

Fig.  584. 


In  all  partial  rubber  cases  where  one  or  more  gum  teeth  or  sectional 
blocks  are  accurately  fitted,  so  that  they  will,  when  the  denture  is  in- 
serted, rest  directly  upon  the  natural  gums,  the  porcelain  teeth  must 
.remain  upon  the  model,  and  be  secured  there  by  the  plaster  which  is 
described  above,  the  investment  should  be  brought  to  the  cutting  edges 
of  both  the  artificial  and  the  plaster  teeth.  The  flashing  of  partial  rub- 
ber cases  often  requires  care  and  forethought.  The  student  Avill  do  well 
to  study  the  case  closely  if  unusual  difficulties  appear,  and  endeavor  to 
devise  some  definite  plan  which  will  seem  to  meet  the  requirements  of 
the  case. 

Packing  the  Case. — The  case  being  ready  for  packing,  the  two  halves 
of  the  flask  are  put  in  a  small  steamer,  which,  as  shown  in  Fig.  585, 
is  a  square  tin  box  having  a  ring  at  the  bottom  for  the  purpose  of 
placing  it  over  any  ordinary  saucepan  that  will  receive  it.  The  box 
has  a  tight  door  and  a  portable  perforated  bottom  resting  over  the  ring, 
provided  with  bars  or  partitions  standing  about  two  inches  in  height  and 
two  and  a  half  inches  apart,  running  back  to  the  full  depth.  By  stand- 
ing the  halves  of  the  flask  edgewise,  resting  against  the  partitions,  and 


496     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

closing  the  door,  the  case  is  quickly  steamed  and  made  hot  for  packing. 
This  arrangement,  as  above  described,  is  very  convenient,  but  any  tin 

Fig.  585. 


or  copper  vessel  in  which  water  can  be  heated  when  provided  with  a  top 
may  be  made  to  answer  the  purpose  nearly  as  well.  The  top  of  the 
steamer  can  be  used  for  warming  the  rubber :  the  latter  should  always 
be  warmed  and  thoroughly  softened  before  it  is  placed  in  the  matrix. 


Before  packing  the  joints  should  be  examined  if  gum  or  block  teeth 
are  used,  and  plaster  mixed  thin  with  water  introduced  into  any  open 
spaces  in  order  to  guard  against  the  ingress  of  rubber.  Zinc  phosphate 
(oxyphosphate)  cement,  mixed  thin  and  worked  between  the  joints  and 


RUBBER  DENTURES.  497 

allowed  to  set,  is  recommended  as  a  reliable  means  of  preventing  the 
rubber  from  being  forced  into  joints. 

Fig.  586  shows  the  upper  section  of  the  flask  with  the  teeth  in  posi- 
tion. The  model  is  then  to  receive  a  coating  of  No.  3  tin-foil  to  pre- 
vent the  rubber  from  penetrating  and  adhering  to  its  surface.  The  tin- 
foil is  made  to  adhere  to  the  plaster  by  means  of  thick  tragacanth  paste 
applied  to  the  model  with  a  suitable  brush.  The  foil  is  cut  into  strips, 
laid  upon  the  model,  and  lightly  burnished  to  the  surface.  Tin-foil 
may  easily  be  removed  from  the  denture  after  vulcanizing  with  the 
finger-nail,  provided  the  surface  of  the  plaster  model  is  hard  and 
smooth ;  but  if  the  plaster  is  soft  and  filled  with  minute  air-bubbles, 
it  will  take  such  a  hold  upon  the  rubber  that  it  can  only  be  removed  by 
the  action  of  an  acid.  Either  of  the  mineral  acids  except  sulphuric  will 
dissolve  it,  but  as  both  nitric  and  nitro-hydrochloric  act  upon  the  rubber, 
the  former  quite  energetically,  neither  should  be  employed  :  hydrochloric 
acid,  though  requiring  a  little  more  time  in  the  solution  of  the  tin,  will 
eifectually  remove  it  without  the  least  effect  upon  the  rubber.  The  con- 
dition of  the  surface  obtained  by  vulcanizing  in  contact  Avith  tin-foil  is 
superior  to  that  produced  by  the  use  of  any  other  of  the  media  usually 
employed  for  the  purpose.  Liquid  silex  and  collodion  are  each  exten- 
sively used  for  the  same  purpose,  but  the  surface  they  afford  is  usually 
inferior  to  that  formed  under  tin-foil.  The  correct  method  of  using 
liquid  silex  is  described  as  follows  by  Dr.  Burchard  : 

"  The  solution  known  by  this  name,  or  as  soluble  glass,  chemically 
the  sodium  silicate  (NajSiOg)  is  quite  as  effective  a  medium  to  prevent 
the  adhesion  of  plaster  to  vulcanite  as  is  tin-foil,  but  certain  precautions 
are  necessary  to  procure  the  best  results.  The  material  should  be  kept 
in  a  moderately  warm  place,  and  tightly  stoppered.  As  soon  as  its 
viscidity  becomes  greater  than  that  of  a  thin  syrup,  throw  it  away  and 
buy  a  new  bottle.  Should  it  lose  its  perfect  clearness,  discard  it.  About 
one-third  of  the  four-ounce  bottles  in  which  it  is  sold  is  useful ;  the 
remainder  is  usually  so  deteriorated  as  to  be  worthless.  Dilution 
with  hot  water  and  warming  the  solution  restore  its  appearance,  but, 
for  dental  purposes,  not  its  virtues.  The  model,  after  investment,  and 
also  the  teeth  and  entire  investment,  are  freed  of  adherent  wax  by 
pouring  over  them  a  stream  of  boiling  water.  The  excess  of  water  is 
absorbed  by  means  of  bibulous  paper.  As  soon  as  the  wet  appear- 
ance disappears  from  the  plaster  it  is  ready  to  receive  the  silicate,  not 
before. 

"A  camel's-hair  brush,  having  a  fine  point  and  no  loose  hairs,  is 
dipped  in  the  solution  and  the  surplus  wiped  off  the  brush.  The  plaster 
surfaces,  all  of  them,  are  painted  lightly  with  the  silex,  carefully  avoiding 
contact  with  the  porcelain  or  platinum  pins.  By  means  of  the  fine  point 
on  the  brush  the  matrix  of  the  rim  is  painted  between  the  teeth ;  in 
coating  the  cap  side  of  the  investment,  much  care  is  required  to  prevent 
touching  the  teeth.  Small  wisps  of  bibulous  paper  are  quickly  and  gently 
passed  over  the  painted  surfaces  until  there  is  but  a  thin  glaze  covering 
every  part  of  the  plaster.  The  pieces  should  be  set  aside  for  at  least 
fifteen  minutes,  to  permit  thorough  hardening  of  the  silex.  After  vul- 
canizing the  flasks  should  not  remain  unopened  over  night,  for  if  salt 
(sodium  chloride)  has  been  used  to  hasten  the  setting  of  the  investment, 

32 


498     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


the  surface  of  the  vulcanized  plate  will  be  covered  by  a  hard  and  tena- 
crous  glass ;  if  opened  as  soon  as  cold  the  plaster  and  silex  part  from 
the  vulcanite,  without  even  washing,  leaving  a  smooth,  glazed  surface 
equal  to  that  found  under  tin-foil." 

The  mechanic  may  be  certain  that  the  lack  of  good  results  is  due  to 
either  carelessness  or  faulty  silex. 

This  is  an  important  matter,  as  unquestionably  many  or  most  of  the 
ills  attributed  to  the  wearing  of  vulcanite  are  due  to  roughness  upon 
the  palatal  surfaces.^ 

The  instruments  used  in  packing  rubber  are  very  simple,  a  couple  of 
blunt-pointed  excavators  being  quite  sujfficient  for  the  purpose.  The 
operator  should  be  very  careful  to  have  his  steam-receptacle,  flask, 
instruments  for  packing,  and  rubber  all  scrupulously  clean,  as  the 
presence  of  wax,  particles  of  plaster,  or  debris  of  any  kind  may 
seriously  impair  the  work. 

The  quantity  of  rubber  required  to  pack  the  case  is  governed  by  the 
thickness  of  the  plate  and  the  length  of  the  bite.  If  the  operator  is  not 
able  to  judge  of  the  amount  of  rubber  which  should  be  used,  he  can  very 

nearly  approximate  the  proper  quantity  by 
Fig.  587.  gathering  together  every  particle  of  the  wax 

that  was  washed   out   from  the   flask   and 
placing    them   in    the    glass   measuring-jar 
containing   water   (Fig.   587).      It   consists 
of  an  ordinary  tumbler,  with  a  dished  cover 
of  spun  brass,  having  a  short  flat  tube  sol- 
3BHi/       dered   into   a   central  opening.     The   trial- 
'^^Ki        plate  is  put  into  the  tumbler,  which  is  nearly 
i^mBII        filled  with  water,  so  that  when  the  cover  is 
imm if         put  on  a  little  will  overflow  into  it  through 
ilMmlf  ^^^^  ^^^  tube.     The  overflow  is  then  thrown 

iliili7  away,  the  trial-plate  removed  and  replaced 

iilBli/  with  rubber.     When  the  water  again  stands 

at  the  top  of  the  tube  the  gauge  contains 
exactly  the  bulk  of  the  trial-plate  in  rubber. 
Rubber  gauge.  The  Small  scctional  area  of  the  tube,  the  only 

escape  which  is  afforded  to  the  water,  ren- 
der the  guage  very  sensitive,  and  an  exact  measurement  may  be  relied 
upon.  The  operation  takes  but  a  few  minutes'  time  and  will  always 
afford  accurate  results.  Another  method  of  gauging  the  amount  of  rub- 
ber required  is  by  weight.  The  specific  gravity  of  brown  rubber  is  about 
twice  as  great  as  that  of  the  wax,  so  that  twice  the  weight  of  wax  in 
rubber  has  about  the  same  volume  as  the  wax. 

In  packing  plain  teeth  it  is  usually  necessary  to  use  pink  rubber  for 
that  portion  of  the  denture  representing  the  gums  :  small  pieces  should  be 
carefully  packed  between  the  teeth ;  a  narrow  band  of  rubber  may  then 
be  laid  along  the  outer  edge  of  the  necks  of  the  teeth  for  the  purpose 
of  uniting  the  small  pieces  together,  followed  by  larger  pieces  until  the 
proper  quantity  to  fill  that  portion  representing  the  gums  has  been 
packed  in.  The  dark  rubber  is  then  to  be  packed  around  the  pins  and 
over  the  palatal  portion.  The  two  are  to  be  worked  alternately,  so  as  to 
1  H.  H.  Burchard,  Cosmos,  July,  1896. 


RUBBER  DENTURES. 


499 


have  the  pink  sufficiently  solid  to  prevent  forcing  the  softer  dark  rubber 
through  the  pink  by  the  final  pressure,  where  it  might  show  in  the  form 
of  dark  spots  on  the  finished  denture.  The  ability  to  accurately  gauge 
the  proportions  will  come  with  a  little  experience  in  this  kind  of  work. 

Should  the  base-plate  wax  be  removed  from  the  flask  en  masse,  the 
amount  of  pink  rubber  required  may  be  thus  measured ;  that  section 
representing  the  artificial  gum  is  to  be  cut  away  and  its  volume  deter- 
mined in  the  water  gauge.  The  pink  rubber  is  then  measured  as  above 
described.  In  these  cases  the  amount  of  brown  rubber  is  to  be  cor- 
respondingly diminished. 

When  the  packing  is  complete  the  flask  is  replaced  in  the  steamer,  and 

Fia.  588.  i 


^-^       ^J^-J 


heated  sufficiently  to  thoroughly  soften  the  rubber  :  the  two  halves  of  the 
flask  are  then  placed  together,  and  closed  by  gradual  pressure  in  one  of  the 
flask  presses  devised  for  that  purpose.  Fig.  588  illustrates  one  which 
has  been  used  with  satisfaction  by  the  author.  The  screw  should  be 
turned  very  slowly,  resting  between  turns  to  allow  the  rubber  to  sj)read 
and  escape  through  the  vents ;  otherwise  there  is  danger  of  breaking 
away  portions  of  the  plaster  investment,  injuring  the  model,  or  of  frac- 
turing the  sectional  blocks  when  that  style  of  teeth  is  used.  When  the 
two  parts  of  the  flask  are  quite  together,  it  may  be  placed  in  a  compress. 


500     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 


as  shown  in  Fig.  589,  and  is  then  ready  for  vulcanizing,  or  in  the  ordi- 
nary bolt  flasks  the  bolts  may  be  adjusted  and  the  flask  secured  by  that 


Fig.  589. 


FiC4.  590. 


means.  The  use  of  bolts  as  a  means  of  forcing  the  parts  of  the  flask 
together  in  packing  is  objectionable  on  account  of  the  liability  to 
stripping  of  the  thread  after  they  have  been  used  a  few  times  :  for  this 
reason  the  press  is  gaining  favor  and  the  bolt  flask  will  probably  fall  into 
disuse. 

VuiiCANIZERS. 

There  are  in  use  at  the  present  time  many  different  forms  of  vul- 
canizers,  each  kind  possessing  more  or  less  merit.  It  would  be  super- 
fluous to  enumerate  them  all :  these  descriptions 
will  therefore  be  confined  to  the  best  and  simplest 
examples  of  the  somewhat  extensive  list.  The 
older  form  is  shown  in  Fig.  590.  The  later  forms 
are  built  after  diiferent  plans.  Among  these  latter 
the  A.  C.  Davis,  and  the  Lewis  cross-bar  vulcan- 
izers  appear  to  possess  the  requirements  of  a  good 
apparatus. 

The  Davis  vulcanizer  (Fig.  591)  is  strong  and 
simple  in  construction.  One  hand  only  is  re- 
quired in  tightening  or  loosening  the  lid,  which  is 
entirely  independent  of  the  hot  chamber. 

The  boiler  or  hot  chamber  is  made  of  heavy 
seamless  copper ;  around  the  top  a  brass  ring  is 
brazed,  forming  a  shoulder  which  rests  upon  a 
steel  collar  bolted  within  the  jacket  to  the  base. 
The  edge  of  the  boiler  fits  neatly  into  a  circular 
groove  in  the  lid,  tightness  of  the  joint  being  secured  by  means  of 
rubber  packing.     The  boiler  is  readily  lifted  out  for  emptying. 


The  Hayes  vulcanizer. 


VULCANIZERS.  501 

The  lid  is  controlled  by  a  centre  screw  and  two  side-guides  on  the 
arras  of  the  yoke  or  cross-bar.  The  cross-bar  is  pivoted  by  its 
upright  arm  at  one  end  to  the  steel  collar  which  supports  the  boiler,  the 

Fig.  591. 


other  arm  being  slotted  to  straddle  a 
stop  at  the  opposite  side  of  the  col- 
lar.    This  pivotal  cross-bar  by  means 

of  a   screw-bolt   passing    through    its  

centre  carries  the   lid  of  the   boiler,  For  kerosene. 

the  bolt  being  operated  by  a  wooden 

hand-wheel,  and,  when  necessary  to  screw  tighter  than  the  wheel, 
a  pin  wrench  is  provided  which  can  be  passed  through  a  hole  in  the 
screw-bolt.  The  thermometer  and  safety-plug  are  secured  to_  the  lid. 
The  centre  screw  with  side-guides  makes  the  movement  of  the  lid  exact, 
and  the  advantages  of  the  swinging  cover  will  be  at  once  apparent  to 
those  who  have  experience  in  the  use  of  vulcanizers.  As  shown  by  the 
illustration,  this  vulcanizer  is  adapted  for  gas,  alcohol,  or  kerosene.^ 

The  Lewis  cross-bar  vulcanizer  (Fig.  592)  is  entirely  new  in  its 
essential  parts,  and  embodies  many  valuable  improvements,  and  is  prob- 
ably one  of  the  strongest,  safest,  and  most  convenient  vulcanizers  of  the 
cross-bar  pattern  in  use. 

The  boiler  is  hand-made  from  copper  rolled  expressly  for  this  form 
of  vulcanizer,  and  is  of  unusual  thickness.  The  cap  is  ribbed  on  the 
under  side  to  resist  any  strain  which  may  be  put  upon  it.  This  cap  has 
but  two  holes  drilled  in  it,  one  for  the  mercury  bath,  to  which  the 
thermometer  is  attached ;  the  other  for  the  "  manifold,"  which  carries 
the  safety-valve,  blow-oif,  gas-regulator,  or  steam-gauge  (Fig.  593).  The 
ring  surrounding  the  boiler  is  of  cast  steel,  and  is  therefore  of  ample 
strength.     Besides  the  lugs  for  taking  the  strain  off  the  cross-bar  and 


502     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 

bolt,  it  has  a  dovetailed  projection  for  the  insertion  of  a  lifting  handle 
(Fig.  594). 

It  will  be  observed  that  when  the  cross-bar  and  cap  are  removed 
there  are  no  swinging  bolts  or  attachments  to  the  pot. 

Fig.  592. 


Lewis  cross-bar  vulcanizer.  with  gas  heating  apparatus. 
Fig.  593. 


The  cross-bar  is  of  an  improved  form,  and  is  also  made  of  cast  steeL 
One  end  is  at  right  angles  to  the  main  bar.  and  terminated  bv  projections 
which  catch  under  the  lugs  on  the  ring.     Over  the  projections  is  a  small 


VULCANIZERS. 


503 


rib  which  prevents  the  bar  from  dropping  out  of  position.  The  other 
end  of  the  cross-bar  has  an  enlarged  portion  for  the  reception  of  the  bolt, 
and  is  terminated  by  a  handle. 

The  vulcanizer  is  closed  by  one  bolt  suspended  in  a  slot  on  the  hand- 
end  of  the  cross-bar.     The  bolt  is  squared  to  prevent  rotation,  and  is 


Fig.  595. 


Pot-lifter. 


Cross-bar  wrench. 


surrounded  by  a  spring  for  the  purpose  of  disengaging  it  from  the  lugs 
when  the  nut  is  slackened  oiF,  and  for  always  retaining  the  bolt  perpen- 
dicularly and  forcing  it  in  place  automatically. 

The  vulcanizer  is  opened  by  loosening  the  nut  on  the  bolt  by  means  of 
the  wrench  furnished  for  the  purpose  (Fig.  595).  The  bolt  will  be  forced 
downward  through  the  action  of  the  spring.     The  handle  of  the  cross- 

FiG.  596. 


bar  is  then  seized,  and  with  the  thumb  against  the  nut  it  is  pressed  until 
the  bottom  of  the  bolt  is  disengaged  from  the  lugs,  when  the  bar  may  be 
lifted  (Fig.  596). 

The  Seabury  Vulcanizer. — This  apparatus  is  so  arranged  that  the 
vulcanizing  is  accomplished  with  dry  steam.  It  has  a  dry  chamber  or 
oven  for  vulcanizing,  which  is  distinct  from  the  steam-generating  chamber 
or  boiler,  the  two  being  connected  by  a  valve  cut-ofF.  The  vulcanizing 
chamber  has  a  capacity  of  three  flasks.  In  the  illustration  the  jacket  is 
cut  away  to  show  the  relative  positions  of  the  two  chambers,  and  their 
connection.  It  is  claimed  for  this  machine  that  plates  made  in  it  are 
as  strong  when  only  half  as  thick  as  when  vulcanized  in  the  ordi- 
nary way. 


504     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 

By  cutting  off  the  steam  from  the  generating  chamber  cases  can  be 
removed  and  others  inserted  without  loss  of  time,  and,  as  the  plaster  is 

Fig.  597. 


but  slightly  injured  by  the  dry  steam,  warping  of  plates  by  the  yielding 
of  the  investment  is  not  likely  to  occur. 

General  Instructions  for  Attaching  and  Connecting  Gas 
AND  Time  Regulators. 

The  gas  regulator  (Fig.  598),  if  not  already  attached  to  the  vulcanizer, 
is  secured  to  the  cap  by  means  of  the  short  iron  pipe  or  coil.  This  is 
screwed  into  a  hole  drilled  through  the  cap  of  the  vulcanizer.  Any  gas- 
fitter  or  machinist  can  connect  the  regulator  to  the  cap  if  he  has  what  is 
known  as  a  ''  one-eighth  gas-pipe  tap."  If  the  vulcanizer  has  a  "  Lewis 
manifold  "  attached  to  the  cap  of  the  vulcanizer,  remove  the  screw  be- 
tween the  blow-off  and  safety-valve  and  screw  the  coil-pipe  in  its  place. 
After  the  gas  regulator  has  been  pro]5erly  fitted,  place  the  vulcanizer  in 
the  jacket  and  in  the  position  in  which  it  is  to  be  used.  Connections 
between  the  time  regulator,  gas  regulator,  and  gas  burner  are  made  by 
means  of  rubber  tubing.  The  engraving  (Fig.  599)  illustrates  the  cor- 
rect method  of  connecting  gas  and  time  regulators  to  vulcanizers.     Cut 


ATTACHING  AND  CONNECTING   GAS  AND  TIME  REGULATORS.  505 


a  piece  of  tubing  of  sufficient  length  to  reach  from  the  gas-supply  tap  to 
the  time  regulator,  and  connect  them  ;  cut  oif  another  piece  to  reach  from 
the  time  regulator  to  the  gas  regulator,  and  attach  to  gas  regulator  by  the 
iij)right  or  straight  nipple  on  top  of  the  No.  4  Lewis  gas  regulator ;  then 
connect  the  downward  curved  tube  of  the  gas  regulator  to  the  gas  burner 
under  the  vulcanizer  with  another  piece  of  rubber  tubing. 

Fig.  598. 


The  time  regulator  is  more  convenient  when  placed  on  a  bracket 
near  the  gas-supply  pipe.  It  is  then  out  of  the  way,  and  not  likely 
to  be  broken  from  contact  with  tools,  and  can  also  be  used  as  a  time- 
piece. 

"  To  Set  the  Time  Regulator. — When  the  valve  lever  on  top  of  the 
time  regulator  (Fig.  600)  is  engaged  with  the  screw  upon  the  minute 
arbor  on  the  back  of  the  clock,  the  valve  is  held  open  for  a  length  of 
time  depending  upon  whether  the  lever  is  engaged  with  the  first,  second, 
or  third  thread  of  the  screw ;  and  the  lever  will  be  cast  off,  and  the 
valve  closed  when  the  minute-hand  reaches  the  figure  XII.  When 
the  minute-hand  is  at  IX  the  lever  will  be  cast  off  at  the  end  of 
fifteen  minutes  if  it  is  engaged  with  the  first  thread  of  the  screw 
from  the  end ;  an  hour  and-  a  quarter,  if  engaged  with  the  second 
thread,  and  so  on.  A  trial  should  be  made,  and  the  time  ascertained 
which  is  necessary  for  heating  the  vulcanizer  to  the  vulcanizing  point, 
and  this  time  should  be  added  to  the  proposed  time  for  vulcanizing. 
Yfe  have,  therefore,  the  following 

"  Rule. — Turn  the  minute-hand  to  as  many  minutes  before  the 
hour  as  the  number  of  odd  minutes  desired ;   then  put  the  end  of  the 


506     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


lever  in  the  threads  of  the  screw  upon  the  minute  arbor  at  the  back  of 
the  clock.    T\\Q  first  thread  from  the  end  gives  the  odd  minutes  to  which 


Fig.  599. 


Fig.  600. 


No.  4  graduated  gas  regulator,  mounted  on  a  Lewis  cross-bar  vulcanizer. 

the  clock  is  set ;   the  next  and  each  succeeding  thread  gives  a  full  hour. 
For  example  :   For  an  hour  and  twenty  minutes  set  the  minute-hand  at 

the  figure  VIII,  and  engage  the  lever  in 
the  second  thread  from  the  end  of  the 
screw.  At  the  end  of  that  time  the  lever 
will  disengage  and  automatically  shut  off 
the  gas  from  the  vulcanizer.  If  this  were 
to  be  an  hour  longer — i.  e.  two  hours  and 
tM^enty  minutes — the  lever  should  be  placed 
on  the  third  thread  of  the  screw. 

"  Those  who  use  vulcanizers  should  be 
thoroughly  informed  as  to  the  nature  and 
properties  of  steam.  The  fact  should  be 
boi^ne  in  mind  that  a  vulcanizer  is  subject 
to  the  same  laws  and  conditions  as  a  steam- 
boiler,  which  it  is  in  fact ;    and,  although  it  is  comparatively  safe  and 


ATTACHING  AND   CONNECTING   GAS  AND   TIME  REGULATORS.  507 

easily  operated,  it  may,  by  carelessness  or  ignorance  in  its  management, 
become  almost  as  dangerous  as  a  bombshell. 

"  The  following  table  of  steam-pressures  will  be  found  convenient  for 
reference,  as  it  has  been  corrected  so  that  it  shows  the  true  temperature 
for  any  pressure  indicated  by  the  steam-gauge.  Fractions  are  omitted, 
and  the  nearest  whole  numbers  used  instead.  The  French  table  gener- 
ally used  shows  14.7  pounds  pressure  at  212°,  whereas  the  steam-gauge 
at  that  temperature  will  indicate  0,  unless  by  the  expansion  of  heated 
air  confined  in  the  vulcanizer.  The  gauge  is  therefore  just  one  atmo- 
sphere lower  than  the  French  table  : 


Table  of  the  Elastic  Force  of  Steam  (corrected  to  correspond  loith  the 

steam-gauge). 


Degrees  of  temperature, 
Fahrenheit. 


212 
220 
230 
240 
250 
260 
270 
280 
290 
300 
310 
320 
330 
340 
350 
360 
370 
380 


Elastic  force  in  lbs.      Degrees  of  temperature, 
per  square  inch.  Fahrenheit. 


0 

2 

6 

10 

15 

21 

27 

34 

43 

52 

63 

75 

89 

104 

120 

140 

160 

180 


390 
400 
410 
420 
430 
440 
450 
460 
470 
480 
490 
500 
510 
520 
530 
540 
550 


Elastic  force  in  lbs. 
per  square  inch. 

.  .  205 

.  .  .  234 

,  .  .  264 

,  .  .  296 

.  .  .  335 

.  .  .  375 

.  .  .  415 

.  .  .  455 

.  .  .  515 

.  .  .  565 

.  .  .  603 

.  .  .  663 

,  .  .  721 

.  .  .  793 

,  .  .  864 

.  .  .  937 

,  .  .  1015 


"  It  will  be  noticed  that  as  the  temperature  rises  the  pressure  of 
steam  increases  in  a  constantly  increasing  ratio  for  equal  increments  of 
heat,  the  pressure  being  nearly  doubled  by  the  addition  of  fifty  degrees 
to  the  temperature.  This  fact  will  show  the  necessity  of  care  and  watch- 
fulness while  vulcanizing. 

"The  bulb  of  the  thermometer  is  set  in  a  mercury  bath.  This  is  the 
small  cup,  forming  a  part  of  the  vulcanizer  cap,  to  which  the  thermome- 
ter case  is  screwed.  This  cup  should  contain  sufficient  mercury  to 
ensure  its  touching  the  bulb  of  the  tube  wKen  the  thermometer  case  is 
screwed  down  properly.  This  makes  a  metallic  connection  between  the 
thermometer  bulb  and  the  vulcanizer  cap,  and  is  absolutely  necessary  for 
the  proper  indication  of  heat  by  the  thermometer. 

"  Should  the  mercury  column  separate,  it  can  usually  be  reunited  by 
removing  the  tube  from  the  thermometer  case,  holding  it  perpendicu- 
larly, and  striking  the  bulb  with  some  force  upon  the  palm  of  the  hand, 
or  by  holding  the  tube  by  the  bulb  and  giving  it  a  sudden  flirt.  If  the 
vulcanizer  is  used  with  the  thermometer  in  this  condition,  it  should  be 
remembered  that  it  is  the  whole  column  that  denotes  the  heat,  and  allow- 
ance should  be  made  for  the  broken  part ;  i.  e.  if  there  is  enough  mer- 
cury separated  to  fill  the  space  of  ten  degrees,  the  remainder  of  the 
column  should  only  rise  to  ten  degrees  less  than  the  temperature  desired. 


508     VULCANIZED  RUBBER,   BASE  FOB  ARTIFICIAL  DENTURES. 

"  Directions  for  inserting  a  new  tube  in  the  thermometer  case  will 
generally  be  found  on  the  package  containing  the  tube  and  scale. 

"  Thermometers  •  are  accurately  marked,  by  test  instruments,  at  the 
212°  and  320°  points,  and  the  scales  are  especially  graduated  for  each 
tube,  as  the  positions  of  the  points  above  named  vary  in  diiferent  tubes. 
Each  tube  must,  therefore,  be  used  with  its  own  scale,  and  in  fitting  it  to  the 
case  care  should  be  taken  that  the  black  mark  on  the  tube  indicating  the 
320°  point  is  brought  exactly  opposite  to  the  320°  point  on  the  scale. 

"  The  thermometer  does  not  always  give  a  correct  indication  of  the 
heat  of  the  vulcanizer.  It  only  gives  the  temperature  of  the  vulcanizer 
top,  which  may  not  be  that  of  the  flask.  In  fact,  the  indications  of  the 
thermometers  employed  on  vulcanizers  are  almost  invariably  too  low, 
owing  to  imperfect  conduction  of  heat,  radiation,  etc. ;  and  the  vulcaniz- 
ing temperature,  instead  of  being  320°,  as  indicated,  is  more  usually 
330°  to  340°." 

The  plan  of  providing  a  mercury  bath  for  the  reception  of  the  bulb 
is  a  great  improvement  over  the  old  way,  and  prevents  the  fracture  of 
the  bulb  by  the  great  pressure  of  the  steam,  which  was  of  such  frequent 
occurrence  when  the  thermometer  was  in  direct  contact  with  the  latter. 

Damage  to  the  glass  bulb  of  the  thermometer  is  manifested  by  a  rise 
in  the  mercury,  which  cannot  be  brought  down  to  the  usual  vulcanizing 
point  by  turning  oflF  the  flame  of  the  burner ;  consequently  the  ther- 
mometer ceases  to  correctly  indicate  the  degree  of  heat,  and  imperfect 
vulcanization  is  the  result.  Leakage  of  steam  around  the  packing  of 
the  vulcanizer  should  also  be  guarded  against,  as  in  such  cases  all  of  the 
water  may  escape  from  the  apparatus  before  the  vulcanizing  is  complete. 
Loss  of  all  of  the  water  in  the  vulcanizer  may  be  detected  by  a  persistent 
fall  of  the  mercury,  even  when  the  gas  flame  is  greatly  increased,  and 
when  this  phenomenon  is  observed  the  gas  should  be  turned  off,  the  vul- 
canizer allowed  to  cool,  and  new  packing  adjusted. 

Failure  to  strictly  observe  this  rule  has  undoubtedly  resulted  in  many 
serious  accidents.  '  An  example  of  this  kind  occurred  some  years  since  in 
the  laboratory  of  the  dental  department  of  the  University  of  Pennsyl- 
vania. A  student  was  endeavoring  to  vulcanize  with  an  apparatus  which 
leaked  at  the  packing  :  noticing  that  the  mercury  persisted  in  falling,  he 
continued  to  increase  the  gas  flame  until  the  lower  part  of  the  vulcanizer 
was  probably  red  hot.  While  he  stood  before  it,  holding  a  lighted  match 
to  the  tube  to  enable  him  to  see  the  column  of  mercury,  the  vulcanizer 
exploded  with  terrific  force,  sending  the  top  through  the  ceiling  and 
pieces  of  the  boiler  in  every  direction.  It  is  quite  likely  that  in  this  par- 
ticular case  the  steam  was  partly  decomposed  by  contact  with  the  hot 
metal,  producing  a  highly  explosive  combination  of  oxygen  and  hydro- 
gen :  no  other  theory  would  seem  to  account  for  the  great  force  of  the 
explosion. 

Having  described  a  few  of  the  different  kinds  of  vulcanizers  and  their 
relative  merits,  we  should  next  consider  how  to  use  them. 

The  flask  or  flasks,  being  ready,  are  placed  in  the  vulcanizer  and 
filled  with  clean  water  to  within  an  inch  or  two  of  the  top.  The  packing 
should  be  smooth  and  sound  ;  a  suitable  separating  material  must  be  ap- 
plied to  the  latter  to  prevent  adhesion  ;  the  joint  between  pot  and  cover 
must  be  absolutely  steam-tight.     A  slight  coating  of  black  lead,  soap- 


FINISHING  PROCESS. 


509 


Fig.  601. 


stone,  or  soap  will  accomplish  the  desired  result,  preference  being  given 

to  the  black  lead.     The  cover  is  then  put  on  as  directed  for  the  diiferent 

kinds  of  vulcanizers ;  the  valve  is  opened  and 

allowed  to  heat  up  until  a  slight  leak  of  steam 

takes  place  :  this  is  to  allow  all   air  to  escape 

before  steam  generates ;  then  close  the  valve  and 

vulcanize,   watching    the    pressure  carefully    if 

there  is  no  automatic  regulator,  so  as  to  keep 

an  even   temperature,  otherwise  the  work  will 

not  be  perfect. 

Fig.  601  shows  a  useful  form  of  flask-tongs 
for  lifting  flasks  from  the  vulcanizer.  They  are 
made  of  sufficient  length  to  reach  the  bottom  of 
a  three-case  vulcanizer,  and  w^ill  securely  grip 
the  flask. 

Finishing-  Process. — After  vulcanizing,  the 
flask  containing  the  rubber  denture  should  be 
allowed  to  cool  gradually  and  completely,  care 
being  taken  not  to  open  the  flask  while  the  least 
warmth  remains  in  the  plaster  investment,  as 
failure  to  strictly  follow  this  rule  will  result  in 
warping  of  the  plate.  The  flask  must  be  opened 
with  care,  and  the  plasster  cut  from  around  the 
teeth  before  attempting  to  remove  it  from  the 
flask ;  otherwise  a  tooth  may  be  broken  or  a 
block  cracked  by  the  use  of  unnecessary  force. 

This  is,  in  fact,  the  most  common  of  causes  in  block  fracture.  All 
traces  of  plaster  should  then  be  carefully  removed,  first  with  a  suitable 
plaster-knife,  and  lastly  with  a  brush  and  water.  The  plate  is  then 
ready  for  trimming  and  polishing. 

Fig.  602. 


Showing  vulcanized  piece  as  it  comes  from  the  investment. 

In  finishing  the  piece  the  surplus  rubber  or  vents  should  be  re- 
moved with  a  jeweller's  saw.  The  buccal,  labial,  and  palatal  edges  are 
then  to  be  filed  to  the  proper  line,  which  is  generally  marked  on  the 


510     VULCANIZED  BUBBEB,  BASE  FOB  ABTIFICIAL  DENTUBES. 

Fig.  603. 


FINISHING  PBOCESS. 


511 


model  with  a  sharp  instrument  before  the  teeth  are  mounted,  and  which, 
showing  on  the  plate  after  vulcanizing,  serves  as  a  guide  to  the  workman 
in  trimming  the  edge  of  the  vulcanized  piece.  Fig.  603  illustrates  a  few 
desirable  forms  of  hies  for  rubber  work. 

The  palatal  portion  and  labial  surfaces  of  the  plate  will  need  but  little 
finishing  if  the  preliminary  waxing  has  been  well  done.  Fig.  602  shows 
a  lower  vulcanite  denture  as  it  should  appear  before  any  attempt  at 
finishing  has  been  made.  It  will  be  seen  by  this  illustration  that  no 
carving  or  scraping  is  necessary,  shape  and  form  having  been  secured  in 
the  wax.  The  correct  thickness  of  the  denture  should  always  be  provided 
for  in  the  temporary  wax-j)late.  A  few  scrapers  of  good  form,  size, 
and  temper  will,  however,  always  be  needed  for  the  removal  of  excres- 
cences which  may  be  present  in  consequence  of  defects  in  the  plaster 
investment,  and  for  this  purpose  the  vulcanite  scrapers  designed  by  Dr. 
N.  W.  Kingsley  will  be  found  to  answer  admirably.  As  shown  in 
Fig.  605,  they  are  superior  to  the  ordinary  scraper.  The  handles  are 
gracefully  formed  to  suit  the  hand  and  steady  the  blade  in  using  its  edge 
to  cut  instead  of  scrape.  The  tool  has  a  rounded  or  convex  back,  with 
thin  edges  :  it  will  not  cut  in,  but  will  remove  superfluous  material  and 
carve  the  surface  smoothly  and  rapidly. 

Two  or  more  gravers  of  the  forms  shown  in  Fig.  604  are  indispensable 
for  trimming  around  the  necks  of  the  teeth  and  carving  the  festoons  of 
the  gums.     These  gravers  should  be  of  a  light  straw  temper,  as  they 

Fig.  604. 


require  considerable  hardness  to  enable  them  to  retain  a  keen  edge  while 
trimming  around  the  necks  of  the  porcelain  teeth.  They  must  be  kept  as 
sharp  as  possible,  so  as  to  make  a  clean  and  smooth  cut  which  will  require 
no  additional  finishing. 

When  the  filing  and  carving  and  unavoidable  scraping  are  finished, 
the  surfaces  thus  worked  over  will  require  additional  smoothing  with 
fine  emery-  or  sand-paper  of  the  grade  of  No.  0  or  00,  or  a  piece  of  quick- 
cutting  Scotch  stone,  kept  wet  and  armed  with  fine  pumice-stone,  followed 
with  a  stick  of  poplar  or  pine  wood  and  pumice  and  water,  will  produce 
a  surface  quite  ready  for  the  final  polishing  on  the  lathe.  Many  materials 
have  been  recommended  as  scratch-eliminators,  and  one  of  the  simplest 
and  most  effective  is  formed  of  an  ordinary  champagne  cork  screwed  on 
to  the  revolving  screw-chuck  and  cut  down  to  the  desired  size  and  shape 


512    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


with  a  pen-knife,  and  worked  with  wet  pumice.  Other  materials,  such  as 
felt,  cotton  cloth,  and  leather,  have  been  used  for  buff  wheels  in  the  fin- 
ishing of  vulcanite  dentures.  An  excellent  set  of  composition  cones  and 
wheels  have  recently  been  introduced,  and  have  been  found  to  be  quite 
equal  to  any  of  their  predecessors.    These  are  shown  in  the  annexed  cut. 

Fig.  605. 


These  buff  wheels,  used  with  pumice,  are  not  intended  for 
obtaining  high  lustre  :  they  are  employed  to  produce  a  condi- 
tion of  surface  suitable  for  the  final  polish,  which  is  obtained 
by  means  of  fine  brush  wheels  armed  with  chalk  or  rouge. 

An  extra  fine  surface  can  be  given  the  plate  by  using 
various  sized  cones  formed  of  moose  hide  armed  with  oil  and 
rotten  stone,  but  the  application  of  the  latter  should  precede 
the  chalk  finish. 

It  is  not  necessary,  of  course,  to  employ  all  of  the  appli- 
ances herein  enumerated  :  any  of  them,  when  used  with  skill 
and  judgment,  will  produce  good  results.  It  should  be  borne 
in  mind  that  no  attempt  to  obtain  a  faultless  surface  will  be 
successful  until  all  tool-marks  and  scratches  have  been  first 
\  J  eliminated  by  rubbing  the  surface  with  fine  emery-paper  and 

pumice  applied  with  a  soft  wooden  stick.  The  latter  method 
is  particularly  effective  in  smoothing  irregular  surfaces  where 
it  is  desirable  to  avoid  obliterating  rugse  and  other  imitations 
of  natural  prominences  of  the  mouth,  as  a  slightly  sharpened 
stick  will  easily  carry  the  abrading  powder  into  deep  places 
which  would  be  inaccessible  to  the  buff  or  brush  wheel, 
1 1 W  After  using  the  felt  buff  wheel,  which  should  follow  the  stick, 

f '  A,  the  surface  may  be  further  improved  by  using  a  coarse  bristle- 
V^^  brush  with  pumice,  kept  freely  wet  with  water.  The  final  pol- 
ishing is  done  with  a  soft  bristle-brush  with  prepared  chalk, 
sparingly  moistened  with  water,  running  the  lathe  at  the  highest  attainable 
speed.  Care  is  required  in  buffing  and  polishing  operations  on  the  lathe 
to  avoid  heating  the  plate  by  the  friction  of  the  rapidly  revolving  wheel. 
Plates  are  often  warped  from  this  cause,  but  by  the  use  of  plenty  of  cold 


FINISHING  PROCESS.  513 

water  during  the  pumicing  and  the  precaution  to  avoid  too  forcible  and 
steady  pressure  during  the  final  polishing  no  such  accident  need  occur. 
The  ebonite  plate  (black  rubber),  with  the  gum  portions  or  fronts 
formed  of  pink  rubber,  generally  requires  two  vulcanizings  in  its  con- 
struction, and  when  tastefully  modelled  and  arranged  the  combination 
of  the  two  rubbers  is  capable  of  affording  a  most  artistic  imitation  of 
a  natural  denture.  A  single  sheet  of  thin  paraffin  and  wax  is  warmed 
and  worked  over  the  model ;  the  edges  are  trimmed  to  the  exact  size 
required  for  the  finished  plate ;  a  narrow  strip  of  wax  is  then  cut  from 
a  sheet  of  wax  to  the  width  and  thickness  of  one-sixteenth  of  an  inch, 
warmed  gently,  and  laid  around  the  outside  buccal  and  labial  edge  and 
along  the  palatal  portion  of  the  plate  just  back  of  the  alveolar  ridge. 
With  a  heated  spatula  this  guard-strip  is  blended  on  the  palatal  side 
with  the  plate.  It  is  then  invested,  packed,  and  vulcanized.  In  vulcan- 
izing black  rubbers  the  temperature  should  be  raised  very  slowly  to 
320°.  The  edges  are  to  be  dressed  and  the  plate  partially  finished, 
and  that  portion  between  the  projecting  borders  which  is  to  receive 
the  teeth  and  pink-rubber  gums  should  be  roughened  thoroughly 
with  a  sharp-pointed  instrument  or  knife-point,  for  the  purpose  of 
ensuring  a  strong  union  between  the  pink  and  black  rubbers.  The 
plate  is  then  ready  for  the  articulation,  which  is  taken  in  the  usual 
way,  after  which  the  teeth  are  selected  and  fitted  :  the  case  is  waxed 

Fig.  606. 


up  and  invested  in  a  flask.  When  the  latter  is  separated  and  the 
wax  thoroughly  removed,  the  surface  which  is  to  be  covered  with  the 
pink  rubber  should  be  given  a  coating  of  a  solution  of  pink  rubber 
dissolved  in  chloroform,  of  the  consistence  of  thick  cream  :  this  is  done 
to  further  strengthen  union  of  the  two  rubbers.  The  piece  is  then  ready 
for  packing  and  vulcanizing.  In  flasking  such  a  case  the  entire  palatal 
portion  of  the  plate  should  be  covered  with  plaster  to  prevent  it  from 
warping  during  packing,  which  otherwise  would  be  liable  to  occur  in 
consequence  of  the  slight  elevation  of  temperature  required  to  soften 
the  pink  rubber  sufficiently  to  admit  of  perfect  closure  of  the  flask. 
This  method  is  illustrated  by  Figs.  606  and  607. 

Partial  Cases. — It  frequently  occurs  in  constructing  partial  artificial 


33 


514     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

dentures  for  the  replacement  of  single  incisors  or  cuspids  that  the  ordi- 
nary rubber  teeth  are  too  thick  to  admit  of  their  being  arranged  to  con- 

FiG.  607. 


Fig.  608. 


form  to  the  line  of  the  natural  teeth  without  interfering  with  the  normal 
occlusion  (Fig.  608).  In  such  cases  a  plate  tooth  may  be  used,  and 
attached,  by  means  of  gold  backings  bent  at  an  angle  with  the  base  of 

the  tooth,  of  sufficient  length  to  allow 
of  the  projecting  portion  being  im- 
bedded in  the  rubber  plate,  as  shown 
in  Figs.  608  and  609.     The  extension 
of  the  gold  backing  should  in  Fig. 
609  bear  two  or  more  holes  punched 
and   countersunk  in  it,  so  as  to  be 
firmly  held  by  the  vulcanized  rubber. 
Gold  clasps  where  used  in  com- 
bination with  rubber  are  attached  in 
the  same  way.     The  clasp,  after  be- 
ing accurately  fitted  to   the   plaster 
tooth,   is   provided  with  a  piece   of 
gold  plate  soldered  at  a  point  next  to 
the  rubber  plate  (Figs.  611-614).     This  attachment  should  be  slightly 
raised  from  the  model,   so  that   it  will   be  entirely  enveloped  by  the 
rubl)er  as  shown  in  Fig.  611. 


Fig.  609.      Fig.  610. 


Fig.  611. 


Fig.  612. 


Fig.  613. 


Fig.  614. 


There  is  some  danger  of  these  clasps  being  forced  slightly  from  their 
correct  position  by  the  pressure  of  the  rubber  in  packing :  this  difficulty 
may  be  entirely  overcome  by  soldering  a  temporary  support  of  scrap 
gold  to  the  clasp  and  bending  it  oyqv  the  plaster  tooth,  as  shown  by 
Fig.  613.     Usually  this  device  will  be  found  to  be  effective  in  retaining 


CLASPS   UPON  VULCANITE  BASE. 


515 


Fig.  615. 


the  clasp  in  contact  with  the  tooth.  After  vulcanizing,  the  supporting 
piece  of  gold  may  be  sawed  off  with  a  jeweller's  saw.  In  packing  a 
case  arranged  with  gold  clasps  a  thin  sheet  of  rubber  should  be  worked 
under  the  gold  attachment  to  further  protect  the  latter  from  displace- 
ment. It  will  of  course  be  understood  that  the  clasps  are  to  remain  in 
position  during  the  packing ;  therefore  in  flashing  such  cases  the  plaster 
should  be  made  to  cover  the  portion  of  the  clasp  not  actually  in  contact 
with  the  rubber :  this  affords  additional  support  to  the  clasp  during  the 
pressure  accompanying  the  closing  of  the  flask  in  packing,  and  will  keep 
it  in  its  correct  relation  to  the  plaster  tooth. 

Partial  Lower  Vulcanite  Dentures. — Gold  is  used  in  combination 
with  that  class  of  partial  lower  dentures  designed  to  replace  the  bicus- 
pids and  molars,  and  when  the  natural  incisors  and  cuspids  remain.  For 
the  purpose  of  strengthening  the  piece 
and  to  lessen  its  bulk  in  front  a  plate 
of  gold  is  sometimes  swaged  to  fit  the 
model  back  of  the  front  teeth,  and 
where  the  ridge  is  not  well  defined  and 
not  favorable  to  the  retention  of  the 
piece  without  some  form  of  attachments,  , 
gold  clasps  are  soldered.  The  gold  plate 
is  allowed  to  extend  somewhat  beyond 
the  cuspid  teeth  ;  the  ends  are  perfora- 
ted by  the  punching  forceps,  as  shown 

by  Fig.  615,  to  ensure  strong  union  with  the  rubber.  This  plate  is 
then  put  upon  the  model  and  secured  in  place  by  means  of  wax  ;  the 
teeth  are  arranged  in  position,  waxed  up,  and  vulcanized  in  the  usual 
way.  The  denture  when  finished  presents  to  view  a  plate  with  the  ante- 
rior part  of  gold,  while  the  two  parts  holding  the  teeth  and  resting  upon 
the  ridge  on  each  side  are  of  vulcanite.     The  purpose  of  such  a  combi- 

FiG.  616. 


nation  is  to  save  labor  and  material,  but  a  denture  so  constructed,  while 
better  in  point  of  durability  and  the  absence  of  bulkiness  where  it 
passes  around  back  of  the  incisors  and  cuspids  than  vulcanite  alone,  is 
still  far  inferior  to  one  constructed  entirely  of  gold,  for  while  such  a 


516     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 

denture  is  doubtless  stronger  than  one  of  vulcanite  alone,  it  is  not  so 
durable  as  one  made  exclusively  of  gold,  on  account  of  the  liability  of 
the  piece  breaking  at  the  points  where  the  gold  is  imbedded  in  the  vul- 
canite. Dentures  of  the  class  above  referred  to  should  always  be  made 
entirely  of  metal,  and  the  expenditure  of  money  and  labor  is  but  little 
greater  than  in  the  combination  plan,  while  the  general  result  is  in 
every  way  more  satisfactory. 

A  simpler,  though  somewhat  inferior,  method  frequently  resorted  to 
in  order  to  strengthen  partial  lower  vulcanite  dentures  and  to  aiford 
means  of  attaching  clasps  is  shown  in  Fig.  616.  It  consists  in  imbed- 
ding a  gold  or  platinum  wire  (Fig.  617)  back  of  the  front  teeth  at  A,  to 
which  clasps  are  soldered,  as  shown  in  B  (Fig.  617).     The  objection 

to  this  arrangement  is  that  it  does  not  re- 
FiG.  617.  duce  the  bulk  of  the  piece  to  any  great 

extent,    while    it   adds   but   little    to   its 
strength. 

Still  another  method  is  by  covering 
that  portion  of  the  lingual  surface  of  the 
plate  back  of  the  natural  teeth  with  the 
perforated  plate  of  Wunsche.  (See  p.  531.) 
Where  the  anterior  natural  teeth  have  become  so  loosened  by  the 
ravages  of  pyorrhoea  alveolaris,  excessive  absorption  of  the  gums  and 
sockets  or  of  the  roots  of  the  teeth,  that  their  complete  loss  is  a  matter 
of  a  very  short  period  of  time,  a  plaster  impression  may  be  taken  of  the 
mouth  before  the  removal  of  the  loose  teeth. 

In  such  cases  the  object  is  to  obtain  an  accurate  plaster  impression 
of  the  mouth  which  shall  include  the  loose  teeth,  and  this  should  be 
done  without  the  exhibition  of  sufficient  force  to  cause  pain  to  the 
patient  or  to  disturb  the  infirm  and  tender  teeth.  This  result  may  be 
attained  by  selecting  a  quite  new  impression-cup  of  proper  size  and 
form,  oiling  the  surface  before  the  plaster  is  placed  in  it,  and  then  pro- 
ceeding in  the  usual  way.  When  the  plaster  is  sufficiently  hard  the  cup, 
in  consequence  of  its  smoothness  of  surface  and  the  oil  applied  as  a 
separating  medium,  may  be  removed  with  very  little  force.  This  leaves 
the  plaster  impression  intact,  and  its  removal  must  be  accomplished  by 
breaking  it  into  sections  with  the  thumb  and  index  finger,  beginning  with 
the  portion  covering  the  labial  surfaces  of  the  incisors,  and  then  removing 
the  plaster  covering  the  buccal  surfaces  of  the  bicuspids  and  molars. 
These  pieces  are  to  be  correctly  assembled  in  the  impression-cup  in  the 
manner  more  fully  described  in  the  chapter  on  Taking  Impressions,  and 
the  model  obtained  in  the  usual  way.  The  plaster  facsimiles  of  the 
infirm  teeth  are  then  to  be  cut  from  the  model  at  the  margin  of  the  gum 
with  a  jeweller's  saw  or  suitable  knife-blade,  and  the  plaster  is  to  be 
scraped  away  to  the  depth  of  three-sixteenths  of  an  inch,  so  as  to  repre- 
sent the  appearance  of  the  socket  immediately  after  the  removal  of  a 
natural  tooth. 

In  constructing  partial  dentures  for  cases  where  the  natural  organs 

are  prematurely  lost  it  is  much  the  better  practice  to  reset  the  natural 

teeth,^  provided,  as  is  often  the  case,  they  are  of  dense  structure  and 

have  not  previously  been  attacked  by  caries.     This  is  done  by  making 

^  Method  of  resetting  natural  teeth,  p.  429. 


MOUNTING   OF  NATURAL   TEETH. 


517 


a  plate  in  the  usual  way,  and  in  the  space  or  spaces  to  be  occupied  by 
the  natural  teeth  vulcanizing  a  strong  platinous  gold  wire,  being  careful 
to  place  the  gold  pin  in  the  centre  of  the  space.  The  wire  must  have 
an  attachment  soldered  to  it,  so  that  its  connection  with  the  rubber  will 
be  secure.  The  wire  may  be  arranged  with  a  simple  piece  of  scrap  gold 
soldered  to  the  end  to  be  imbedded  in  the  rubber,  as  shown  in  Fig.  618, 
or  it  may  be  provided  with  a  perforated  extension,  as  shown  in  Fig. 
619,  by  which  union  with  the  rubber  may  be  secured  and  great  bulki- 
ness  avoided.  The  rubber  portion  of  the  denture  finished,  it  only 
remains  to  remove  the  infirm  natural  organs  and  attach  them  to  the 
plate  made  ready  for  their  reception.  This  is  done  by  sawing  off  the 
roots  (Fig.  618),  enlarging  the  pulp-canal  with  a  suitable  engine  drill, 
fitting  the  neck  of  the  tooth  to  the  plate,  and  into  the  socket,  as  shown 
in  same  figures,  and  then  attaching  the   tooth  to  the  pin  (Fig.  619) 

Fig.  618. 


and  plate  by  means  of  zinc-phosphate  cement,  being  careful  to  dry  the 
parts  thoroughly  before  the  cement  is  applied.  This  method  of  reset- 
ting natural  teeth  is  more  conveniently  done  on  gold  plates  than  on 
those  of  rubber,  but  it  is  applicable  to  both.     It  possesses  the  following 


Fig.  619. 


advantages  :  First.  The  teeth  are  the  patient's  natural  teeth,  and  this  fact 
very  greatly  lessens  the  repugnance  which  many  individuals  of  exalted 
sensibilities  feel  to  artificial  teeth.  Second.  It  saves  the  individual  from 
being  seen  without  teeth — a  matter  of  the  greatest  importance  to  many 
patients.  Third.  Artificial  appearance  is  avoided,  for  they  are  the 
natural  teeth  of  the  patient,  and  nothing  more  need  be  said  on  the  score 
of  natural  eifect.     The  question  is  often  asked,  Do  teeth  reset  in  this 


518     VULCANIZED  RUBBER,  BASE  FOB  ABTIFICIAL  DENTURES. 

manner  suffer  from  dental  caries  ?  It  has  been  observed  that  such  teeth 
are  not  more  liable  to  decay  after  their  attachment  to  a  plate  than  they 
were  before  removal  from  their  sockets. 

It  might  be  thought  that  irritation  of  the  freshly  wounded  alveoli 
would  be  caused  by  the  teeth  covering  and  to  some  extent  entering 
them  ;  on  the  contrary,  wounds  incident  to  extraction  heal  more  rapidly 
when  covered  by  a  denture  than  when  left  quite  open. 

If  the  infirm  natural  teeth  are  of  poor  quality  and  have  large  fillings 
in  them,  it  is  better  to  use  porcelain  teeth,  and  the  dentures  can  be 
entirely  finished  ready  for  insertion  before  the  natural  teeth  need  be 
extracted.  Care  should  be  observed  to  allow  the  necks  of  the  artificial 
teeth  to  extend  well  into  the  sockets  of  the  extracted  organs,  to  anticipate 
absorption  of  the  parts  which  to  some  extent  is  sure  to  occur  at  such 
points. 

In  all  partial  upper  dentures,  wherever  practicable,  the  teeth  should 
rest  upon  the  natural  gum,  and  where  excessive  absorption  has  occurred 
and  fulness  is  demanded,  gum  teeth  are  preferable  to  the  use  of  pink 
rubber. 

When  dentures  are  inserted  soon  after  extraction  the  use  of  plain 
teeth  is  invariably  indicated,  especially  at  the  anterior  ])ortion  of  the 
mouth,  including  the  incisors  and  cuspids.  These  should  be  ground  to 
fit  the  gum  accurately,  and  to  ensure  close  adaptation,  the  plaster  model 
should  be  slightly  scraped  away  at  the  points  where  the  necks  of  the 
teeth  rest  upon  it.  In  flasking  cases  wherein  the  teeth  rest  directly  upon 
the  plaster  model  it  is  well  to  arrange  the  plaster  investment  so  that  the 
teeth  may  remain  in  situ  during  the  packing — i.  e.  in  the  lower  section  of 
the  flask  and  not  separate  from  the  model  by  the  removal  of  the  second 
half  of  the  flask,  as  is  usually  the  case. 

Repairing  Rubber  Plates. — Breakage  of  vulcanite  dentures  is  usu- 
ally due  either  to  over-vulcanizing,  by  which  elasticity  and  toughness  are 
destroyed,  or  to  improper  arrangement  of  the  molars,  by  which  the  strain 
of  mastication  is  thrown  on  the  outside  instead  of  on  top  of  the  ridge,  as 
shown  in  Figs.  620  and  621. 

Figs.  620  and  621. 


Correct  way.  Incorrect  way. 


The  first  evidence  of  the  giving  way  of  the  piece  is  usually  a  fine  crack 
appearing  between  the  two  central  teeth,  and  sometimes,  in  partial  den- 
tures, in  the  border  surrounding  a  natural  tooth,  as  shown  by  Fig.  622.  A 
break  of  this  nature  may  be  repaired  by  riveting  a  neatly-fitting  piece  of 
stout  platinous  gold  plate  over  the  crack,  as  shown  in  same  figure.  The 
rivets  should  be  of  18-carat  gold  wire,  of  the  size  of  No.  16  of  the  stand- 
ard gauge,  and  the  holes  for  the  reception  of  the  rivets  should  be  coun- 
tersunk on  both  sides.  After  annealing  the  wire  it  should  be  screwed  in 
a  hand  vise,  so  that  a  head  may  be  formed  upon  the  end  by  spreading 


REPAIRING    VULCANITE  PLATES. 


519 


the  metal  with  a  small  riveting  hammer  :  the  wire  is  then  passed  through 
the  rubber  and  the  gold  plate,  the  head  portion  of  the  pin  resting  in  the 


Fig.  622. 


countersunk  portion  of  the  vulcanite  plate.  After  cutting  off  the  wire  with 
a  pair  of  wire-cutters  until  but  little  of  the  rivet  projects  beyond  the  gold 
plate,  the  ends  of  the  pins  are  spread  with  the  riveting  hammer  until 
they  fill  the  countersunk  holes  in  the  small  metallic  plate,  and  draw  the 
latter  in  close  contact  with  the  rubber.  The  edges  of  the  plate  should 
be  bevelled,  and  the  rivets  smoothed  with  a  fine  corundum  wheel,  fol- 
lowed by  the  Scotch  stone,  so  that  no  roughness  or  projection  will  remain 
to  annoy  or  abrade  the  tongue.  Fractures  of  plates  at  such  points  is 
usually  guarded  against  at  the  time  the  denture  is  constructed,  by  im- 
bedding a  semilunar  section  of  the  perforated  aluminum  plate  of  Wunsche 
in  the  rubber  while  packing  in  case. 

Another  method,  particularly  applicable  to  plates  which  are  broken 
entirely  in  two,  consists  in  adjusting  the  two  parts  of  the  plate  together, 
and  fastening  them  in  correct  relation  to  each  other  temporarily  by  ad- 
hesive wax  and  shellac  dropped  on  the  lingual  surface  until  plaster  can 
be  run  into  the  palatal  portion  of  the  denture.  As  soon  as  the  plaster 
hardens  the  plate  is  removed  from  the  model,  the  line  of  division  enlarged 
with  the  file,  and  dovetails  cut  opposite  each  other  with  a  jeweller's  saw, 
as  shown  by  Fig.  623.  The  dove- 
tailed space  is  then  filled  with  wax, 
invested  in  the  usual  way  in  a  flask, 
packed,  and  vulcanized.  This  method 
is  open  to  one  serious  objection  :  it 
necessitates  another  vulcanizing  and 
the  consequent  loss  of  elasticity  and 
toughness ;  a  plate  so  treated  will 
never  be  as  strong  as  it  was  before. 
Or  the  edges  may  be  adjusted  as 
before  described,  and  the  piece 
placed  immediately  in  the  lower 
half  of  the  flask  :  after  the  plaster 
has  set  the  adhesive  wax  is  to  be 
removed  from  the  lingual  side  of  the  plate,  and  a  line  cut  with  a  round 
engine  bur  along  to  the  full  extent  of  the  crack  or  break,  halfway  through 


520     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

the  plate  and  a  quarter  of  an  inch  wide,  with  smooth,  regular  edges,  with- 
out dovetails.  The  case  is  then  waxed  up  and  the  other  half  of  the  flask 
poured  :  when  the  piece  is  ready  for  packing  the  surface  of  the  break  is 
coated  with  a  thick  solution  of  rubber  in  naphtha ;  the  case  is  then 
packed  and  vulcanized.  If  the  parts  have  been  kept  perfectly  clean, 
the  union  will  be  quite  strong. 

To  avoid  loss  of  strength  by  the  second  vulcanizing  it  has  been  re- 
commended that  fusible  metal,  melting  at  150°  F.  or  160°  F.,  be  used 
to  fill  the  dovetailed  space.  This  can  be  done  by  pouring  the  melted 
alloy  into  the  space  and  packing  it  with  a  hot  spatula,  which  is  readily 
admissible  owing  to  the  low  fusing-point  of  the  metal.  While  this 
method  has  the  advantage  of  not  requiring  a  second  vulcanizing,  the 
union  of  the  metal  at  the  point  of  fracture  is  not  as  close  as  when  rubber 
is  used,  and  it  cannot  be  said  to  be  reliable  as  a  means  of  repairing 
broken  rubber  plates. 

Much  the  better  way  is  to  fasten  the  parts  together,  run  a  plaster 
model  into  the  denture,  then  make  a  bite  of  plaster  to  serve  as  a  guide 
for  the  replacement  of  the  teeth,  remove  the  latter  from  the  broken  plate, 
reset  them  to  the  model,  wax  up  the  piece,  flask. 
Fig.  624.  ^j^^j  vulcanize.     This  aflbrds  practically  a  new 

case,  and  the  time  consumed  is  not  much  greater 
than  is  required  in  repairing  the  old  one. 

Another  method  for  hastily  mending  broken 
rubber  dentures  is  as  follows :  After  adjusting 
the  broken  parts  and  making  the  model  for  the 
palatal  side,  cut  through  half  the  depth  of  the 
plate  from  end  to  end  of  the  break  for  an  eighth 
of  an  inch  in  width  on  each  side  of  the  crack : 
undercut  the  edges,  drill  several  holes  through 
the  plate,  countersinking  them  on  the  palatal 
side.  Cut  a  piece  of  Wunsche's  perforated  metal 
the  desired  size,  press  it  flat  into  the  groove,  and 
pour  fusible  metal  over  it  until  level  with  the 
surface  of  the  plate;  when  cool  dress  down  and  finish.  A  neat  and 
comparatively  secure  mend  may  be  secured  in  this  way.  Fig.  625  shows 
a  finished  piece. 

Additions  of  teeth  to  old  plates  are  accomplished  after  practically  the 
same  methods.  Fig.  625  shows  a  case  where  six  teeth  had  been  extracted, 
and  the  old  plate  is  prepared  for  the  addition  of  as  many  porcelain  teeth, 
so  that  the  denture  could  be  worn  until  the  absorption  of  the  alveoli 
and  gums  would  admit  of  the  construction  of  a  permanent  plate.  The 
illustration  shows  the  plate  bevelled  off  to  a  smooth  edge,  and  several 
holes  drilled  into  the  filed  portion.  The  correct  occlusion  of  the  new 
teeth  is  obtained  by  placing  the  plate  in  the  mouth  after  the  bleeding 
ceases,  and  placing  two  pieces  of  softened  wax  along  the  alveolar  ridge 
and  plate,  and  directing  the  patient  to  bite  into  the  wax,  and  then  gently 
pressing  the  wax  while  the  teeth  are  in  contact :  this  gives  the  correct 
relation  of  the  lower  to  the  upper  teeth,  and  the  impression  of  that  por- 
tion of  the  alveolar  ridge  to  be  covered  by  the  addition  to  the  plate.  The 
preparation  of  the  plaster  model  and  bite  is  done  in  the  usual  way,  plain 
teeth  being  ground  to  the  gums  to  allow  for  the  rapid  absorption  which 


COMBINATION  DENTURES. 


521 


always  follows  the  extraction  of  teeth.     The  waxing  and  flasking  are 
done  in  the  usual  way.    The  filed  surface  of  the  plate  is  then  to  be  coated 


Fig.  625. 


Fig.  626. 


with  rubber  solution,  packed,  vulcanized,  and  finished.     Fig.  626  shows 
the  completed  case,  the  faint  lines  in- 
dicating the  point  of  union  of  the  old 
and  new  rubber. 

Combination  Dentures. — Under 
this  heading  are  included  metal  plates 
with  vulcanite  attachments,  vulcanite 
plates  with  metal  linings,  vulcanite 
dentures  strengthened  with  perforated 
metal  plates,  vulcanite  in  combination 
with  the  continuous-gum  method,  etc. 
Excellent  results  may  be  obtained  by 
attaching  the  teeth  to  metallic  plates 
by  means  of  vulcanized  rubber.  A 
denture  so  constructed  will  be  found  to 
possess  greater  strength  than   one   of 

vulcanite  alone,  while  it  will  have  the  additional  advantage  of  being 
free  from  interstices,  which  favor  the  lodgement  of  decomposable  debris. 
In  other  words,  the  combination  of  metal  plate  with  vulcanite  attach- 
ment thoroughly  meets  the  objections  raised  against  either  method  alone. 

Either  gold,  silver,  platinum,  aluminum,  or  any  of  their  alloys  usually 
employed  in  prosthetic  dentistry  may  be  used  in  the  construction  of  one 
of  these  combination  dentures ;  preference,  however,  should  be  given  to 
gold  as  a  base.  Platinum  unalloyed  is  not  well  adapted  for  the  purpose, 
on  account  of  its  great  ductility  and  weight,  but  when  alloyed  with  a 
small  percentage  of  iridium  its  rigidity  is  so  much  increased  that  a  plate 
of  No.  29  thickness  will  be  found  to  be  quite  as  strong  as  a  much  thicker 
plate  of  18-carat  gold. 

Either  ordinary  silver  plate  of  standard  ^  fineness  may  be  used  with 

1  Coin. 


522    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

rubber  attachment,  or  silver  alloyed  with  platinum,  the  latter  having 
greater  tensile  strength  than  the  former.  It  must  be  remembered,  how- 
ever, that  silver  has  a  powerful  affinity  for  sulphur,  the  indurating  agent 
in  vulcanite,  and  that  the  presence  of  platinum  as  an  alloy  does  not 
entirely  protect  the  silver  from  the  action  of  the  sulphur.  It  is  there- 
fore necessary,  where  a  silver  plate  is  used,  to  interpose  a  layer  of  No.  60 
tin-foil  between  the  rubber  and  the  plate ;  this  precaution,  however,  is 
not  necessary  where  celluloid  is  used. 

In  silver  dentures  with  vulcanite  attachments  the  anchorages  must  in- 
variably be  made  of  platinum  or  gold  wire.  After  the  plaster  wall  is  made 
and  the  wax  removed  from  around  the  teeth,  the  exact  positions  of  the 
anchorages  are  marked  upon  the  plate  with  a  sharp  steel  point  to  the 
number  of  eight  or  ten.  The  plate  is  then  laid  on  a  charcoal  support, 
and  pieces  of  silver  solder  are  fused  at  the  points  indicated.  The  wire 
is  then  cut  into  proper  lengths,  screwed  in  a  vise,  and  one  end  of  each 
flattened  by  means  of  a  rivetting  hammer  into  the  form  of  a  head  :  each 
pin  is  then  taken  up  separately,  the  headed  end  dipped  in  borax,  and 
placed  on  the  plate  at  a  point  where  a  piece  of'  solder  has  been  fused. 
The  borax  will  assist  in  retaining  the  piece  of  wire  until  the  flame  of 
the  blowpipe  is  directed  upon  it  to  remelt  the  solder  and  unite  the  pin 
to  the  plate.  The  wire  anchorages  are  not  to  be  bent  into  hook  form,  as 
shown  in  Fig.  629,  until  after  the  tin-foil  protection  has  been  adjusted. 
The  pins  are  forced  through  the  tin-foil  and  pressed  with  a  rubber  point, 
and  burnished  closely  to  the  plate.  The  holes  made  by  the  passage  of 
the  pins  through  the  tin-foil,  if  care  is  used,  will  not  be  large  enough  to 
allow  the  rubber  to  reach  the  silver  to  any  great  extent.  After  the  tin 
is  in  place  the  pins  may  be  bent  with  pliers,  as  shown  in  Fig.  629. 

Another  method  is  by  directly  tinning  the  surface  to  be  covered  by 
the  rubber.  The  silver  is  cleansed  and  covered  with  a  saturated  solution 
of  zinc  chloride.  The  tin-foil  is  pressed  carefully  against  the  silver  and 
the  plate  is  held  above  a  Bunsen  flame  until  the  tin  fuses.  Its  flowing 
is  to  be  directed  by  means  of  a  camel's-hair  pencil  which  has  been 
dipped  in  the  zinc  solution. 

Vulcanite  in  Comhinaiion  with  Plates  of  Fusible  Alloy. — For  the 
modus  operandi  in  the  preparation  of  plates  of  fusible  alloys  the  reader 
is  referred  to  Chapter  XIV.  Figs.  551  and  552  satisfactorily  illustrate 
upper  and  lower  fusible  metal  plates  prepared  for  vulcanite  attachments. 
The  Reese  or  Weston  fusible  alloys  can  be  cast  very  thin,  and  yet  be 
sufficiently  rigid  to  withstand  the  force  of  mastication.  These  alloys 
retain  their  color  and  make  an  admirable  combination  plate.  Having  fin- 
ished the  plates  as  shown  above,  the  edges  and  raised  rims  are  trimmed 
to  the  desired  dimensions.  A  roll  of  softened  gutta-percha  or  wax  is 
pressed  around  the  gums  over  the  alveolar  ridges,  and  trimmed  with  a 
knife  to  the  supposed  height  of  the  teeth.  The  plates  are  then  tried  in 
the  mouth,  and  the  wax  trimmed  from  all  sides  until  perfect  occlusion 
and  contour  are  obtained.  The  median  line  is  marked  on  the  gutta- 
percha or  wax,  as  the  case  may  be,  and  the  cutting  edges  marked  in 
several  places  to  serve  as  guides  in  restoring  the  upper  and  lower  waxes 
to  their  correct  relation  to  each  other  should  they  become  separated. 
The  articulating  models  are  prepared  in  the  usual  way — pouring  plaster 
into  the   lower  plate,  first  allowing  it  to   extend  back   sufficiently   to 


COMBINATION  DENTURES.  523 

receive  the  upper  half,  which  is  to  be  poured  next.  The  gutta-percha 
is  then  to  be  removed  and  the  teeth  arranged  and  waxed  up  and  vul- 
canized. The  attachment  of  the  vulcanite  to  the  plate  may  be  secured 
by  freely  nicking  the  ridge  to  which  the  teeth  are  to  be  fastened  by 
means  of  a  sharp-pointed  graver,  but  without  this  the  undercut  of  the 
rims  and  buttons  will  be  ample  to  hold  the  vulcanite  securely  to  the 
metal. 

Aluminum,  though  not  affected  by  sulphur,  is  not  as  well  suited  for 
vulcanite  attachments  as  the  other  metals  named,  on  account  of  the  want 
of  reliable  aluminum  solder  with  which  to  fasten  the  loops  or  pins  thor- 
oughly ;  but  by  special  treatment,  which  will  be  described  in  connection 
with  the  manner  of  preparing  aluminum  plates,  a  comparatively  durable 
denture  can  be  made  of  that  metal  with  vulcanite. 

In  constructing  a  denture  of  gold  with  vulcanite  attachments  the 
plate  should  be  of  the  thickness  of  No.  27  of  the  standard  gauge,  and 
made  in  accordance  witli  the  directions  for  the  making  of  gold  and  silver 
plates  in  Chapter  IX. 

It  should  be  provided  with  a  rim  extending  entirely  around  the  labial 
and  buccal  edges  and  upon  the  palatal  portion  of  the  plate  slightly  pos- 
terior to  the  alveolar  ridge,  as  shown  by  A  and  B,  in  Fig.  627.     This  rim 


Fig.  627.  Fig.  628. 


may  be  soldered,  or  swaged  as  shown  by  Fig.  628.  If  soldered,  it  may 
be  formed  of  No.  27  plate  or  round  wire  of  No.  17  gauge.  A  rim 
formed  of  round  or  triangular  wire  requires  much  less  labor  and  time  in 
its  adjustment  than  if  formed  of  a  strip  of  plate,  and  when  flattened 
with  the  file  on  the  labial  side,  and  the  corundum  wheel  and  graver  on 
the  palatal  side,  it  has  the  same  effect  as  if  it  was  formed  of  plate. 

The  rim  may  be  dispensed  with  entirely,  but,  as  it  gives  a  more 
finished  appearance  to  the  denture  and  adds  greatly  to  its  strength,  it 
should  therefore  always  be  preferred. 

In  attaching  a  flat  rim  to  a  gold  or  silver  plate  a  strip  of  plate  long 
enough  to  extend  entirely  around  the  rubber  attachment  should  be 
cut,  as  shown  by  Fig.  632.  The  rim  should  be  annealed,  and  bent 
with  the  pliers  to  fit  the  labial  and  buccal  edges  on  the  plate.  It  is 
then  placed  on  a  charcoal  support,  and  the  rim  held  in  contact  with  the 
plate  by  means  of  small  nails  or  tacks  :  it  is  then  united  to  the  plate  by 
a  small  piece  of  solder  immediately  in  front  at  the  frsenum  and  at 
one  or  two  other  points  along   the    buccal  edges.     The  plate  is  then 


524    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


cooled,  placed  upon  the  plaster  model,  and  with  a  small  hammer  and 
pliers  the  rim  is  brought  in  close  enough  contact  with  the  plate  to 


Fig.  629. 


admit  of  complete  soldering.  The  palatal  portion  of  the  rim  should 
not  be  soldered  to  the  plate  until  after  the  correct  position  of  the  teeth 
has  been  ascertained.  This  is  accomplished  by  arranging  the  teeth 
according  to  the  bite  and  other  requirements  of  the  case,  and  then 
making  a  wall  of  plaster  around  them,  separated  at  the  centre  line. 
This  enables  the  operator  to  mark  upon  the  plate  with  a  sharp  instru- 
ment the  correct  point  at  which  to  solder  the  rim,  so  that  it  will  leave 
an  unbroken  surface  for  the  tongue,  as  shown  by  B  in  Fig.  627,  and  to 
mark  the  proper  position  for  the  loops  or  bent-pin  attachments,  as  shown 
by  A  in  Fig.  628.  It  is  very  important  that  the  exact  location  of  these 
fastenings  should  be  ascertained,  but  this  cannot  be  determined  until 
after  the  teeth  have  been  adjusted.  Any  attempt  to  solder  the  rim  or 
fastenings  previous  to  the  fitting  and  arrangement  of  the  teeth  will  be 
but  guesswork,  and  nearly  always  results  in  either  of  the  conditions 
shown  in  Figs.  630  and  631. 


Fig.  630. 


Fig.  631. 


The  wire  rim  is  soldered  to  its  place  by  simply  clamping  the  wire  to 
the  plate,  and  then  attaching  it  at  single  points  in  front  and  at  the 
buccal  edges,  and,  after  the  correct  position  of  the  teeth  has  been  ascer- 
tained, bringing  it  entirely  around  at  the  palatal  portion,  as  shown  by 
C  in  Fig.  629.  By  simple  pressure  with  an  instrument  or  gently  tap- 
ping with  a  riveting  hammer  it  may  be  brought  into  close  contact  with 
the  plate  and  completely  soldered.  It  need  not  be  flattened  and  finished 
until  after  the  case  is  vulcanized. 


COMBINATION  DENTURES. 


525 


In  soldering  the  flat  or  plate  rim  it  is  necessary  to  hold  the  rim  in 
contact  with  the  plate  for  the  preliminary  attachment;  care  must  be 


Fig.  632. 


Fig.  633. 


exercised  to  avoid  springing  or  warping  the  plate.     The  small  nails  or 


526     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


carpet  tacks  used  to  hold  the  rim  to  the  plate  should  be  fixed  at  points 
shown  in  Fig,  632,  and  never  on  each  side  of  the  plate,  as  shown  by 
Fig.  633.  The  greatest  expansion  occurs  across  the  broadest  part  of  the 
plate,  and  if  it  is  confined  at  that  point,  and  then  heated  to  redness,  it 
will  invariably  be  found  warped  to  such  an  extent  that  its  adaptation  to 
the  model  will  be  impaired. 

Instead  of  an  inside  rim,  some  mechanical  dentists  prefer  to  form  the 
air-chamber  in  the  shape  of  a  horseshoe,  as  shown  in  Fig.  634. 

Fig.  634. 


Fig.  628  gives  a  sectional  view  of  the  arrangement.  AA  represents 
the  vulcanite  attachment,  B  the  metal  plate,  G  the  air-chamber  blending 
at  its  lower  edge  with  the  plate  and  at  its  upper  with  the  vulcanite, 
leaving  an  unbroken  surface  for  the  tongue.  This  form  of  air-chamber 
is  well  adapted  to  swaged  aluminum  plates  designed  for  vulcanite 
attachments.  With  the  outer  rim  also  turned  up  in  the  swaging,  it 
aifords  nearly  the  same  eifect  as  the  soldered  continuous  rim  above 
described.     Fig.  635  shows  a  plaster  model  with  wax  arranged  previous 

Fig.  635. 


to  the  making  of  dies  and  counter-dies,  so  that  chamber  and  rim  may 
be  swaged  from  one  piece  of  metal. 

Owing  to  the  difficulty  in   soldering  alimiinum,  it  is  necessary  to 
secure  attachment  for  the  vulcanite  to  the  plate  by  means  of  perforations 


COMBINATION  DENTURES. 


527 


Fig.  636. 


"m 


or  countersunk  holes  along  the  top  of  the 
ridge.  For  this  purpose  ingenious  per- 
forating punches  have  been  devised  by 
Drs.  Richmond  and  Peck,  as  shown  by 
Figs.  636  and  637,  the  latter  throwing 
up  a  sharp  square  bur,  the  other  a  loop. 
The  punch  points  entering  from  the  under 
side  of  the  plate  produce  the  desired  result 
without  in  the  least  bending  or  affecting 
the  fit  of  the  plate. 

A  rolled  aluminum  plate,  constructed 
in  the  manner  shown  by  Fig.  634  and 
roughened  by  means  of  the  punches  (Figs. 
636"  or  637),  and  with  the  teeth  attached 
by  means  of  vulcanite,  will  afford  a  light, 
strong,  and  comparatively  durable  denture. 

Dr.  J.  W.  Hollingsworth^  of  Green 
Castle,  Indiana,  describes  a  method  of  pre- 
paring aluminum  plates  for  vulcanite  at- 
tachments, as  follows  :  "  Perforate  the  ridge 
of  the  plate  at  proper  points  and  intervals ; 
then  pass  through  these  perforations,  from 
the  inner  surface  of  the  plate,  headed  pins 
made  of  aluminum,  which,  after  replacing 


Fig.  637. 


Perforating  forceps  No.  9. 
Fig.  638. 


Loop  punch. 


^  Richardson's  Mechanical  Dentistry. 


528     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

the  plate  with  the  pins  back  upon  the  die,  are  shrunken  down  to  per- 
manency with  a  hollow  punch.  The  punch  must  be  made  with  the  hole 
not  quite  equal  in  depth  to  the  length  of  the  extruding  portion  of  the 
pins  and  slightly  bell-mouthed.  The  riveting  process  forms  seriate 
studs  or  pins,  which  may  be  bent  or  flattened  with  pliers  in  any  way  to 
suit  the  requirements  of  the  case." 

Continuous -gum  and  Vulcanite  Combination.  —  A  continuous-gum 
front  is  made  on  a  platinum  plate  of  the  usual  thickness  (No.  29),  of 
sufficient  width  to  fit  the  alveolar  ridge,  extending  back  of  the  ridge  far 
enough  to  admit  of  the  edge  of  the  plate  being  turned  up  sufficiently  to 
engage  the  vulcanite  palatal  portion  of  the  plate.  This  turned  edge  is 
perforated  at  close  intervals  with  the  plate-punch,  so  that  the  union  of 
the  vulcanite  with  the  plate  may  be  strong.  On  the  labial  and  buccal 
surfaces  the  platinum  plate  should  reach  as  high  as  the  porcelain  is  to 
extend.  The  plate  is  to  be  made  in  the  manner  usual  in  continuous- 
gum  work,  with  swaged  rim,  etc.,  the  only  difference  being  that  a  stout 
platinum  wire  is  soldered  across  from  one  extremity  of  the  plate  to  the 
other  to  prevent  warping  during  exposure  to  the  high  temperature  of 
the  furnace  :  this  wire  is  to  be  removed  when  the  piece  is  ready  for  the 
vulcanite  palatal  portion.     (See  Fig.  639.) 

Fig.  639. 


Showing  platinum  wire  support. 


The  fitting  and  soldering  of  the  teeth  and  the  application  and  fusing 
of  the  porcelain  body  and  enamel  are  to  be  done  as  described  in  the 
chapter  on  the  Continuous-gum  Process.  The  ductility  of  platinum  is 
greatly  increased  by  high  temperature  :  it  is  therefore  necessary  that  all 
parts  of  the  plate  should  be  well  supported  during  the  fusing  of  the  body 
and  enamel.  This  may  be  accomplished  by  placing  it  upon  a  bed  of 
coarse  silex  and  carefully  building  the  silex  up  to  and  under  the  plate, 
so  that  no  part  of  it  can  sag  when  exposed  to  the  fusing-point  of  the 
body.  After  the  several  burnings  are  complete,  the  plate  is  placed  on 
the  plaster  model  and  the  portion  to  be  formed  of  vulcanite  represented 
in  wax,  flasked,  packed,  vulcanized,  and  finished. 

This  is  the  only  practical  method  of  combining  vulcanite  with  con- 


COMBINATION  DENTURE. 


529 


tinuous  gum.  It  has,  however,  not  found  much  favor  with  dental 
prosthetists  for  obvious  reasons. 

Vulcanite  is  of  great  value  in  refitting  gold  plates  which  have  ceased 
to  fit  the  mouth  in  consequence  of  changes  by  absorption  following  the 
extraction  of  the  teeth.  These  changes  may  continue  in  some  cases  for 
several  years  after  the  removal  of  the  natural  organs,  to  such  an  extent 
finally  that  the  denture  will  no  longer  be  of  service.  The  absorption 
usually  occurs  along  the  alveolar  ridge,  and  it  is  a  matter  requiring  but 
little  time  or  labor  to  adjust  the  denture  to  a  new  plaster  model,  fill  the 
spaces  caused  by  absorption  with  wax,  invest,  pack,  and  vulcanize  the 
piece.  Care  must  be  observed  to  make  countersunk  perforations  through 
the  plate  at  points  where  the  vulcanite  is  to  be  attached,  so  as  to  secure 
firm  union  with  the  gold  plate. 

Vulcanite  Plates  lined  with  Gold-foil,  Electro-deposits,  etc. — Various 
experiments  have  been  made  with  this  class  of  work  in  the  last  twenty- 
five  years,  with  a  view  to  developing  some  process  by  which  a  durable 
metallic  coating  can  be  given  to  that  portion  of  the  vulcanite  denture 
which  is  in  contact  with  the  alveolar  and  palatal  portion  of  the  mouth. 
There  are  two  methods  :  one  consists  in  coating  the  surface  of  the  plaster 
model  with  gold  by  electro-deposition,  by  first  rendering  it  impervious 
to  warm  water,  so  that  it  will  not  take  up  and  destroy  the  gold  bath. 
The  surface  to  be  electro-plated  must  be  hard  and  smooth  and  free  from 


Fig.  640. 


The  vulcan  gold  lining. 

all  greasy  substances.  It  must  be  thoroughly  coated  with  plumbago  and 
painted  with  a  solution  of  chloride  of  gold  to  facilitate  rapid  deposition 
over  the  whole  surface. 

The  next  and  simplest  form  is  to  coat  sheets  of  No.  8  or  10  gold-foil 
with  a  non-conductor  on  one  side,  or  by  putting  two  sheets  together  with 
a  non-conductor — as  wax,  for  instance — between  them,  and  sealing  the 
edges  with  wax  to  prevent  the  gold  solution  from  penetrating  between 
or  through  the  sheets.  A  rough  granular  coating  of  gold  or  copper  can 
be  deposited  on  the  exposed  sides,  which  will  ensure  comparatively  good 
adhesion  with  the  plate  after  vulcanizing. 

34 


530    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

Another  method  is  what  is  known  as  the  "  Vulcan  gold  lining."  It 
is  a  pure  gold  sheet  covered  on  one  side  with  a  thin  coating  of  silver 
(Fig.  640).  The  gold  is  applied  in  one  piece  to  the  surface  to  be  covered, 
and  no  extra  care  is  required  in  packing  the  flask.  The  lining  is  of 
chemically  pure  gold  on  one  side  with  a  thin  covering  of  pure  silver  on 
the  other.  The  union  between  the  rubber  plate  and  the  gold  lining  is 
mechanical :  the  sulphur  in  the  rubber  acting  upon  the  surface  of  the 
silver  produces  a  condition  of  surface  which  favors  adhesion. 

This  foil  is  of  the  thickness  of  No.  40.  In  applying  it,  the  case  should 
be  packed  first ;  the  flask  is  then  separated,  and  any  imperfections  in  the 
model  are  to  be  repaired  with  thin  plaster  or  oxyphosphate  cement.  The 
model  is  then  to  be  painted  with  a  thin  solution  of  equal  parts  of  shellac 
and  sandarac  dissolved  in  alcohol.  When  dry,  coat  the  surface  with 
dextrin,  gum  tragacanth,  or  damar  varnish,  and  while  still  moist  and 
sticky  press  small  pieces  of  the  gold  lining  on  to  the  model,  bright  side 
down.  The  gold  lining  is  first  cut  into  convenient  strips  of  the  form  of 
oblongs,  squares,  and  triangles,  to  avoid  wrinkling.  The  edges  should 
slightly  overlap,  and  the  lining  be  kept  free  from  varnish  or  any  sub- 
stance that  would  be  likely  to  interfere  with  adhesion.  Pressure  on  the 
granular  side  of  the  foil  with  a  steel  instrument  should  also  be  avoided. 
The  rubber  end  of  a  lead  pencil  or  the  finger  is  the  best  means  of 
pressing  the  gold  into  all  the  irregularities  of  the  model.  The  flask 
should  then  be  carefully  closed  and  the  piece  vulcanized. 

Dr.  Joseph  Speyer  has  introduced  a  method  of  lining  vulcanite  and 
celluloid  dentures  consisting  of  a  thin  metallic  plate  of  the  thickness  of 
No.  120  foil,  the  surface  of  which  is  covered  with  minute  papilliform 
prominences  (shown  in  Fig.  645,  magnified  four  diameters),  which  are 
claimed  to  effect  very  strong  surface  cohesion,  while  they  cause  no  irri- 
tation and  leave  no  marked  indentations  on  the  tissues.  The  forms 
illustrated  by  Fig.  644  are  made  of  gold  with  one  side  covered  with  a 
thin  layer  of  silver.  In  vulcanizing  the  surface  of  the  silver  is  corroded 
by  the  sulphur,  causing  it  to  adhere  to  the  vulcanite  with  great  tenacity. 

Speyer's  Adhesive  Plate. — Another  device  of  the  same  inventor 
consists  of  a  layer  of  an  unvulcanizable  rubber  plate  which  is  attached 


Fig.  642. 


Fig.  643. 


Showing  Speyer's  adhesive 
plate  for  upper  dentures. 


Showing  the  adhesive  plate       Showing  finished  denture, 
for  lower  dentures. 


to  the  palatal  surface  of  vulcanite  plates ;  the  preparation  of  which  it  is 
composed  yields  slightly,  and  furnishes  a  firmer  adhesion  than  does  the 
hard,  smooth  surface  of  vulcanized  rubber  (Figs.  641,  642,  643). 

After  the  wax  is  boiled  out  and  the  case  packed,  the  flask  closed,  then 
reopened,  the  adhesive  plate  is  trimmed  so  as  to  cover  the  entire  palatal 


COMBINATION  DENTURES. 


531 


surface  of  the  rubber.  It  is  then  softened  by  dipping  it  in  warm  water, 
laid  on  the  rubber,  tin-foil  side  up,  and  the  flask  closed.  In  vulcanizing 
the  adhesive  plate  incorporates  with  the  rubber,  and  will  be  found  to 
cover  the  entire  interior  surface  of  the  plate  on  the  palatal  side.  After 
vulcanizing  the  tin-foil  is  removed. 

The  adhesive  plate  can  be  vulcanized  to  the  palatal  surface  of  old 
plates,  producing  strong  adhesion  and  obviating  the  necessity  of  making 
a  new  plate. 


Fig.  644. 


Fig.  645. 


Surface-cohesion  forms  for  artificial  dentures. 


Combination  of  Vulcanite  with  Perforated  Plates. — Gold  and  plat- 
inum gauze  has  been  used  as  a  means  of  strengthening  vulcanite  den- 
tures as  long  ago  as  1865.      Dr.  Robert  Wunsche  of  Germany  has 


Fig.  646. 


Combination  dentures. 


devised  ^  a  perforated  plate  which  has  found  favor  with  many  of  the 
most  skilful  prosthetists  in  this  country  and  abroad.  These  perforated 
plates  are  stamped  from  gold,  aluminum,  and  Victoria  metal,  and  are 
very  light  and  strong.     Fig.  646  shows  one  of  the  perforated  plates  as 


532     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 


prepared  for  use.  A  part  of  the  plate  on  the  right  shows  the  perfora- 
tions as  they  appear  under  a  strong  magnifier.  It  will  be  seen  that  the 
holes  are  countersunk,  so  that  when  the  rubber  is  forced  through  it 
forms  a  head  or  clinch  on  the  face  of  the  plate,  making  it  impossible  to 
detach  the  plate  by  any  ordinary  force.  It  is  claimed  that  by  the  use 
of  this  plate  a  lighter,  thinner,  and  stronger  plate  can  be  made  than  by 
vulcanite  alone,  and  such  a  combination  presents  the  novel  appearance 
of  a  reticulate  metallic  structure  with  vulcanite  filling  the  coned  inter- 
stices. It  is  also  thought  to  be  better  from  a  hygienic  standpoint  for  the 
tongue  and  mucous  membrane,  on  account  of  the  conducting  quality  of 
the  metal,  than  vulcanite  alone.  Figs.  647  and  648  illustrate  two  par- 
tial dentures  made  by  Dr.  Wunsche.    Fig.  647  shows  the  lingual  portion 


Fig.  647. 


Fig.  648. 


of  the  plate  with  the  reticulate  form  used.  Fig.  649  illustrates  another 
form  of  perforation,  which  is  diamond-shaped  and  presents  an  artistic 
appearance  when  finished. 

Fig.  649. 


In  the  application  of  perforated  plates  it  is  desirable  to  obtain  two 
models  of  the  mouth,  reserving  the  best  one  for  vulcanizing  on,  and 
utilizing  the  other  in  obtaining  a  zinc  die  and  lead  counter-die  with 
which  to  swage  the  perforated  plate. 

Dr.  Wunsche  gives  the  following  description  of  his  method  of  apply- 
ing the  perforated  plate  which  bears  his  name  :  "  The  counter-die  is  best 
obtained  by  first  burnishing  on  to  model  No.  2  a  thin  tea-lead  or  pattern- 
tin  plate,  over  which,  after  oiling  the  exposed  plaster  surface,  the  thick- 
mixed  plaster  can  be  poured  to  form  the  counter-cast.     When  separated 


COMBINATION  DENTURES.  533 

the  tin  plate  is  to  be  flattened  and  laid  on  the  combination  plate  as  a 
pattern  for  cutting  an  approximation  to  the  size  and  shape  of  the  per- 
forated blank.  This  blank  is  then  heated  slightly  and  carefully  when 
aluminum  is  used,  on  account  of  its  low  fusing-point,  and  pressed  gently 
with  the  fingers  on  to  the  No.  2  model,  over  which  a  piece  of  thin,  soft, 
wet  muslin  has  first  been  laid  to  keep  the  plaster  out  of  the  perforations, 
the  smaller  mouths  of  which  lie  next  the  muslin.  Another  piece  of  wet 
muslin  is  laid  on  the  plate,  and  with  the  counter-model  gentle  hand- 
pressure  is  made  to  partially  conform  the  plate.  This  plate  is  then  an- 
nealed, put  between  the  wet  muslins  on  the  No.  2  model,  and,  with  the 
counter-die  in  place,  is  put  under  a  screw-press  and  softly  pressed  to 
shape.  The  case  is  then  opened,  closely  cut  to  fit  margins,  annealed, 
replaced,  and  tightly  pressed  into  place.  Due  care  and  caution  should 
be  observed  to  prevent  and  overcome  any  tendency  to  wrinkle :  a 
smooth,  nearly  conforming  plate  may  thus  be  made  to  fit  the  deepest 
vault  or  most  irregular  ridge. 

If  a  vacuum  chamber  is  contemplated,  provision  must  be  made  for  it 
in  the  plaster  model  as  usual.  If  the  Speyer  plate  (shown  in  Fig.  644)  is 
proposed,  a  suitable  piece  of  the  adhesive  plate  metal  must  be  placed  on 
the  No.  2  model,  the  cup  mouths  toward  the  model,  and  pressed  by  the 
counter-die  into  place,  and  shaped  before  proceeding  to  make  the  com- 
bination plate  as  previously  described. 

Model  No.  1  having  been  placed  in  the  articulator  after  obtaining  the 
bite,  a  very  thin  wax  plate  is  put  on  ;  the  combination  plate  is  warmed 
and  neatly  pressed  into  place,  so  that  the  wax  will  come  through  the 
perforations  and  by  nice  manipulation  be  made  flush  with  the  metal  sur- 
face, which  must  not  be  covered  with  the  wax. 

The  flasking  and  vulcanizing  are  done  as  usual,  excepting  the  time 
of  exposure,  which  is  lengthened  twenty  minutes  to  make  a  harder  vul- 
canite, and  thus  strengthen  the  reticulate  metal,  and  with  it  form  a  com- 
bination plate  of  remarkable  strength,  stiffiiess,  and  artistic  appearance. 
Either  pink  or  black  rubber  may  be  used ;  the  latter,  however,  makes  a 
stronger  plate. 

For  partial  dentures  having  isolated  teeth — as  two  laterals,  for  ex- 
ample— the  perforated  metal  is  of  great  advantage  in  strengthening 
the  thin  isthmus  which  connects  each  artificial  lateral  tooth  with  the 
plate. 

In  every  case  the  finishing  process  should  remove  from  the  lingual 
surface  only  the  vulcanite  overlapping  the  metal ;  the  latter  should  not 
be  scraped,  but  merely  polished  with  its  enclosed  vulcanite.  When 
properly  modelled  in  waxing  the  finishing  is  but  the  work  of  a  few 
minutes,  and  the  resulting  light  and  thin  plate  will  be  sufficiently  strong 
and  exceedingly  artistic  in  appearance. 

Figs.  650  and  651  show  a  full  upper  denture  with  the  metallic  net- 
work, having  the  pink  rubber  between. 

Fig.  651  shows  a  denture  with  plain  teeth,  pink  rubber  in  front,  gold 
lined  on  the  palatal  side,  with  a  vacuum  chamber  made  with  the  Speyer- 
Fenner  suction  surface  of  aluminum.  By  this  combination  a  denture 
may  be  constructed  possessing  lightness,  strength,  and  cleanliness.  In 
the  case  shown  by  Fig.  651  the  waxing  was  done  with  precision,  and  tin- 
foil was  burnished  over  the  labial  portion,  so  that  after  vulcanizing  it 


534     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

required  no  other  finishing  than  the  mere  use  of  the  brush-wheel  in  the 
final  polishing. 

Two  comparatively  new  kinds  of  rubber  have  been  introduced  within 

Fig.  650. 


two  or  three  years  that  commend  themselves  for  use  in  the  combination 
plate  described  above.     One  is  the  "  granular-gum  "  rubber  facing  by 


Fig.  651. 


Fig.  652. 


Dr.  Gilbert  Walker,  in  the  use  of  which  the  following  directions  are 
given  :  "  In  waxing  up  a  case,  carefully  model  the  gum  portions  to  the 

exact  contour  desired,  and  make  fes- 
toons smooth  at  the  necks  of  the 
teeth.  After  flashing,  face  with  a 
layer  of  granular  gum  cut  to  lie  close 
around  the  labial  and  buccal  necks 
of  the  teeth,  and  pack  against  the 
outer  wall  of  the  plaster  investment, 
so  that  the  facing  shall  not  extend 
above  the  edges  of  the  plaster.  Lap 
the  pieces  of  granular  gum  carefully, 
so  that  the  red  rubber  will  not  be 
squeezed  between  them,  and  show 
on  the  facing  after  vulcanizing.  In 
packing  the  red  rubber  care  must  be  taken  not  to  have  an  excess,  else 
the  overflow  may  carry  with  it  the  granular  gum  and  elongate  its  colored 


COMBINATION  DENTURES. 


535 


particles,  thus  interfering  with  the  mosaic  appearance  on  which  the  imi- 
tation of  the  gum  depends. 

The  palatal  part  of  the  plate  may  likewise  be  faced,  with  care  in 
lapping  the  pieces  of  granular  gum  and  avoiding  an  overplus  of  red 
rubber.  With  this  form  of  rubber  exposure  to  sunlight  for  the  purpose 
of  developing  its  color  is  unnecessary ;  when  well  polished  the  moisture 
of  the  mouth  will  improve  the  tint. 

Granular  gum  vulcanizes  with  any  of  the  ordinary  rubbers ;  better 
results  are,  however,  obtained  by  vulcanizing  it  at  a  low  temperature. 
In  finishing  care  should  be  exercised  to  avoid  cutting  through  the  thin 
facing. 

Gear's  shaded  pink  rubber  is  somewhat  similar  to  the  granular  gum 
described  above.  It  may  be  used  in  the  same  manner  as  the  latter,  and 
adds  greatly  to  the  beauty  and  natural  appearance  of  the  gum  portion 
of  the  denture  if  the  preliminary  modelling  has  been  done  with  taste  and 
skill. 

Beaded  or  Grooved  Vulcanite  Dentures. — For  the  more  complete  ex- 
clusion of  air  and  moisture  from  between  the  artificial  denture  and  the 
mucous  membrane  upon  which  it  rests  a  groove  is  cut  in  the  plaster 
model,  as  shown  in  Fig.  653,^  so  that  the  vulcanized  denture  should  have  an 
integral  half-round  smooth  bead  formed  on  its  vault  aspect,  as  in  Fig.  654.^ 
The  groove  must  be  carried  continuously  across  the  palatal  portion  of 
the  plaster  model  and  along  the  buccal  and  labial  lines  of  muscle  attach- 
ments, to  form  a  bead-enclosure  which  should  produce  a  supplemental 
chamber-like  function  of  the  entire  inner  surface  of  the  denture  (Figs. 
653  and  654). 

Fig.  653. 


This  bead  is  of  especial  value  in  cases  where  no  chamber  is  used,  and 
in  connection  Avith  the  chamber  it  greatly  increases  the  amount  of  atmo- 
spheric adhesion. 

It  may  be  applied  to.  partial  dentures,  as  shown  in  Fig.  655.^  Care 
must  be  observed  in  removing  the  denture  from  the  flask  and  in  freeing 
it  from  the  plaster,  that  the  bead  is  not  accidentally  damaged  or  cut 
through  at  one  or  more  points  by  the  plaster-knife.     The  groove  may 

'  Dental  Cosmos,  July,  1895,  p.  582.  ■■'  Ibid.  ^  Ibid. 


536     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 


be  conveniently  scraped  on  the  plaster  model  by  one  of  the  larger-sized 
Palmer's  excavators,  which,  being  rounded  at  its  cutting  edge,  will 
afford  a  half-round  bead  in  the  vulcanized  piece. 

Plates  made  from  wax   impressions  and  those  which   have  become 
slightly  warped  in   polishing,  or   where  the  gum  in    consequence   of 


Fig.  654. 


Fig.  655. 


absorption  following  the  loss  of  teeth  shrinks  away  from  the  plate,  may 
need  slight  bending  to  secure  closer  contact  with  the  palatal  portion  of 
the  mouth.  This  may  be  safely  accomplished  by  oiling  the  palatal  sur- 
face of  the  plate  and  running  plaster  into  it  to  form  a  model.  When 
hard  the  plate  is  to  be  removed  and  the  plaster  model  scraped  aw^ay  to 
an  extent  corresponding  with  the  amount  of  change  required  to  bring  the 
edge  of  the  plate  in  close  contact  with  the  tissues.  The  plate  is  then  to 
be  coated  with  olive  oil  to  prevent  burning,  heated  over  a  spirit  lamp, 
and  when  sufficiently  pliable  placed  upon  the  model,  previously  warmed, 
and,  Avith  a  piece  of  chamois  skin  laid  over  the  portion  to  be  bent,  press 
it  home  with  the  finger,  a  tooth-brush  handle,  or  a  large  ball  burnisher, 
and  hold  firmly  until  cold. 

Weighted.  Vulcanite  Dentures  and  Dentures  with  Plumpers. — 
As  a  rule,  lower  dentures  formed  of  vulcanite  have  not  sufficient  weight 
to  overcome  the  resistance  of  the  muscles  of  the  cheeks  and  the  sub- 
lingual integuments,  and  when  the  bite  is  unusually  short  they  are  also 
deficient  in  strength,  so  that  breakage  of  lower  dentures  is  a  common 
occurrence.  Both  of  these  defects  may  be  remedied  by  constructing  a 
platinum  or  gold  plate  of  two  thicknesses  of  No.  29,  soldering  suitable 
anchorages  near  the  top  of  the  ridge  in  a  position  which  will  not  inter- 
fere with  the  teeth,  and  vulcanize  as  described  under  the  heading  of 
Combination  Dentures. 

A  less  expensive  method  of  adding  weight  to  a  vulcanite  denture 
consists  in  using  rubber,  which  is  prepared  for  the  purpose  with  tin 
filings  incorporated  in  it.  By  this  means  the  requirements  as  to  weight 
are  very  nearly  fulfilled,  but  no  additional  strength  is  acquired,  the  only 
means  of  overcoming  that  difficulty  being  the  use  of  a  metallic  plate. 

When  the  bite  is  unusually  long  it  may  be  waxed  and  flasked  in  the 
usual  manner,  and  after  the  flask  has  been  separated  preparatory  to  pack- 


COMBINATION  DENTURES.  537 

ing  a  cylindrical  rod  of  wax  may  be  laid  upon  the  under  sides  of  the 
blocks  or  single  teeth,  as  the  case  may  be,  of  sufficient  length  to  extend 
from  one  finishing  molar  to  the  other.  The  wax  rod  is  then  carefully 
lifted  from  its  place  and  invested  in  plaster  to  form  a  mould  which 
should  be  in  two  equal  halves,  the  line  of  division  being  exactly  in  the 
centre  of  the  diameter  of  the  wax  rod.  This  mould  should  have  a 
gate  bored  through  the  top  for  convenience  in  pouring  melted  tin,  while 
at  the  other  extremity  it  should  be  provided  with  a  vent  to  allow  of  the 
escape  of  air  at  the  instant  of  pouring  the  melted  tin.  The  tin  may  be 
melted  in  a  small  iron  ladle  with  a  suitable  handle,  and  the  melting  may 
easily  be  accomplished  over  a  gas-jet  or  alcohol  flame.  When  the  cast- 
ing is  complete  and  the  tin  sufficiently  cool,  the  mould  may  be  opened 
and  the  tin  facsimile  of  the  wax  rod  placed  in  position  in  the  flask,  rest- 
ing upon  the  teeth,  as  previously  indicated  in  the  description  of  the 
preparation  of  the  wax  pattern  rod.  The  tin  rod  should  be  so  arranged 
that  all  parts  of  it  will  be  covered  by  the  vulcanite.  Fig. 
656  shows  the  arrangement  as  described,  A  indicating  Fig.  656. 

the  tin,  B  the  vulcanite.  This  method  possesses  the 
additional  advantage  of  preventing  porosity  of  the  vul- 
canite— an  accident  which  is  very  liable  to  occur  in 
bulky  lower  dentures. 

It  is  sometimes  necessary  to  amplify  the  denture  at 
points  where  unnatural  depression  occurs  in  consequence 
of  great  absorption  following  the  loss  of  cuspids  or 
molars.  If  the  amount  of  projection  required  to  restore 
natural  expression  is  not  extraordinary,  slight  additions 
to  the  rim  and  the  usual  vulcanizing  may  be  relied  upon  to  accom- 
plish the  desired  result ;  but  if  the  case  require  a  large  mass,  exceeding 
a  quarter  of  an  inch  in  thickness,  the  vulcanizing  must  be  done  at  a 
lower  temperature,  of,  say,  300°  F.,  and  three  hours'  exposure  in  the  vul- 
canizer,  in  order  to  avoid  porosity.  Equally  good  results  may  also  be 
attained  by  forming  a  core  of  some  light  material,  enveloping  it  in 
rubber,  and  with  it  filling  the  recess  in  the  flask  representing  the 
^'  plumper."  For  this  purpose  cores  of  thin  metal  hermetically  sealed, 
approximating  the  form  of  the  plumper  and  one-eighth  of  an  inch 
smaller  than  the  latter  may  be  used.  The  preparation  of  metallic  forms 
is,  however,  a  matter  requiring  considerable  labor  and  time.  A  much 
simpler  and  equally  effective  method  is  to  form  a  core  either  of  vulcan- 
ized rubber  sponge  or  cotton  wool  tightly  rolled  and  wrapped  with 
thread.  In  packing  the  core  is  not  to  be  placed  in  position  until  the  case 
has  been  packed  and  the  flask  completely  brought  together,  when  it  may 
be  opened,  the  recesses  representing  the  plumpers  freed  from  rubber, 
and  the  cores,  previously  wrapped  with  strips  of  soft  rubber  to  the 
thickness  of  an  eighth  of  an  inch,  put  in  its  place.  The  object  of  first 
packing  and  closing  the  flask  is  to  prevent  the  flow  of  rubber  from  dis- 
placing the  cores  and  to  ensure  their  complete  envelopment.  In  finishing 
such  a  case  care  must  be  exercised  to  avoid  cutting  through  the  rubber 
and  exposing  the  sponge  or  cotton  when  those  materials  are  used.  Prob- 
ably of  the  materials  named  a  piece  of  hard  vulcanite  affi)rds  the  best 
results  and  is  less  likely  to  lead  to  failure  through  displacement,  which 
is  always  liable  to  occur. 


538     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

The  same  course  as  outlined  above  in  the  preparation  of  ordinary 
plumpers  may  be  pursued  in  making  plates  to  restore  contours  when 
large  portions  of  the  maxillary  bones  have  been  lost  by  disease  or  acci- 
dent, such  as  gimshot  wounds,  etc.     Fig.  657   shows  a  model  of  the 

Fig.  657. 


mouth  of  a  syphilitic  subject  in  which  the  whole  anterior  portion  of  the 
alveolar  ridge  had  been  removed,  leaving  a  large  opening,  A,  into  the 
nasal  cavity,  by  which  speech  was  seriously  affected.  After  obtaining 
the  model  a  thin  plate  of  wax  was  prepared  to  cover  the  palatal  portion 
(as  shown  in  Fig.  658)  extending  around  the  teeth  in  the  form  of  half 
clasps,  and  through  the  opening  A  in  Fig.  657  even  with  the  floor  of 
the  nasal  cavity.     A  narrow  strip  of  wax  was  then  built  around  the 

Fig.  658. 


labial  edge  A  (Fig.  658),  and  another  around  the  palatal  border  of  the 
ridge,  as  shown  by  B.  After  smoothing  down  and  blending  the  wax 
with  the  palatal  portion  of  the  plate  by  means  of  a  hot  spatula,  a  hollow 
space,  C,  remained  at  the  point  where  the  alveolar  ridge  had  been  re- 
moved during  surgical  treatment.     The  Avax  plate  thus  prepared  was 


VULCANITE  PLATES   WITH  FLEXIBLE  RUBBER  RIMS.        539 

invested  in  an  ordinary  flask  and  vulcanized  in  black  rubber,  as  shown 
in  Fig.  658.  When  finished  the  hollow  space  C  was  filled  in  with  a 
mixture  of  sand  and  plaster  to  form  a  core,  and  dressed  to  the  inner 
edges  of  A  and  B  (Fig.  658)  to  represent  the  lost  portion  of  the  alveolar 
ridge.  Placing  the  plate  in  the  mouth  with  some  softened  wax  along 
the  ridge,  the  patient  was  requested  to  bite  into  it,  thus  forming  the 
occlusion.  After  pouring  the  under  side  of  the  plate  the  articulating 
model  was  made  as  usual.  The  teeth  were  fitted  and  arranged,  and 
waxed  to  the  outer  edges  of  A  and  B  projections.  The  case  was  then 
flasked  and  vulcanized  in  the  usual  way.  When  entirely  finished  a  hole 
was  drilled  through  the  projection  which  filled  the  opening  to  the  nasal 
cavity,  and  another  through  the  end  resting  against  the  right  molar : 
through  these  openings  the  core  of  sand  and  plaster  was  removed  by 
means  of  a  wire ;  when  quite  empty  the  openings  were  securely  sealed. 
Speech  was  entirely  restored  by  the  fixture,  which  was  light  and  strong 
and  did  good  service  for  many  years. 

Vulcanite  dentures  are  occasionally  retained  in  situ  by  means  of 
spiral  springs.  This  method  of  retention  is,  however,  but  seldom  re- 
sorted to,  except  in  cases  of  extreme  flatness  of  the  mouth  or  else  in  the 
correction  of  oral  deformities.  (For  a  description  of  the  preparation 
and  adjustment  of  spiral  springs  the  reader  is  referred  to  Chapter  XIII.) 

Vulcanite  Plates  with  Flexible  Rubber  Rims. — The  use  of  flexi- 
ble rubbers  in  connection  with  artificial  dentures  is  of  doubtful  value, 
on  account  of  the  inevitable  loss  of  flexibility  of  all  semi-vulcanizable 
rubbers  when  worn  in  the  mouth.  The  term  of  durability  of  a  flexible 
rim  is  but  a  few  months,  but  its  advocates  claim  that  its  object  will  have 
been  attained  by  that  time,  and  that  the  patient  will  have  acquired  the 
ability  to  retain  the  plate  without  it. 

In  the  construction  of  such  a  plate  a  line  should  be  carefully  made 

Fig.  659. 


on  the  model  entirely  around  the  outride  of  the  alveolar  ridge  and  across 
the  posterior  border  of  the  hard  palate.  The  line  should  not  be  carried 
too  high  at  the  point  occupied  by  the  buccinator  muscles,  and  it  should 
indicate  the  extent  of  the  outer  edge  of  the  plate  when  finished  ;  it  must 
be  sunk  to  the  depth  of  a  thirty-second  of  an  inch  all  around,  and 
tapered  to  the  width  of  an  eighth  of  an  inch,  blending  with  the  model 


540     VULCANIZED  RUBBER,  BASE  FOB  ARTIFICIAL  DENTURES. 

at  the  inner  margin  (Fig.  659).  In  this  groove  two  thicknesses  of 
velum  rubber,  which  can  be  obtained  from  any  dental  depot,  should  be 
laid.  The  rubber  may  be  made  to  adhere  to  the  model  by  first  coating 
the  latter  with  a  solution  of  the  rubber  dissolved  in  chloroform,  which 
will  retain  it  in  position  while  waxing  up  (Fig.  660).     The  model  is 

Fig.  660. 


then  to  be  covered  with  a  thin  plate  of  paraffin  and  wax,  allowing  it  to 
extend  over  the  flexible  rubber  rim  one  half.  The  wax  is  to  be  trimmed 
carefully,  so  that  the  edge  will  be  sharp  and  clearly  defined,  and  care 
should  be  observed  that  no  melted  wax  is  allowed  to  touch  the  outer 
portion  of  the  flexible  rim,  as  its  flexibility  would  be  impaired  by  com- 
bination with  wax.  The  teeth  are  mounted  and  flashed  in  the  manner 
already  described,  except  that  it  is  necessary  to  cover  the  exposed  rim 
of  flexible  rubber  with  a  good  body  of  plaster  to  ensure  its  retention  in 
position.  (See  sectional  cut,  Fig.  660,  A  representing  the  model ;  B,  B, 
the  flask ;  C  the  hard  vulcanite  plate,  and  showing  the  dovetail  joint 
with  D,  D,  the  flexible  rubber  rim ;  E,  E,  the  plaster  investment 
securely  holding  it  in  position  during  packing  and  vulcanizing.)  It  is 
essential  to  have  a  solid  body  of  plaster  over  the  soft  rim  to  prevent  the 
hard  rubber  from  finding  its  way  in  and  affecting  its  flexibility.  The 
finishing  of  the  plate  after  vulcanizing  is  the  same  as  heretofore  given. 
The  necessity  for  care  in  the  arrangement  of  the  flexible  rim  to  the 
model  becomes  apparent.  Since  it  is  not  possible  to  trim  and  polish 
rubbers  of  that  class  after  vulcanizing,  their  condition  of  surface  will 
depend  upon  the  state  of  the  matrix  in  which  they  are  moulded. 

Pink  Vulcanite  in  Combination  -with  Soldered  Dentures. — One 
of  the  most  important  applications  of  vulcanizable  rubbers  is  its  combina- 
tion with  plain  teeth,  where  it  is  often  employed  to  form  the  rim  and 
gums  and  to  supply  at  appropriate  points  sufficient  bulk  (plumpers)  to 
restore  the  natural  contour  of  the  face. 

When  used  to  form  the  gums  in  connection  with  plain  teeth  it  affords 
a  denture  possessing  distinct  advantages  over  one  formed  of  single  gum 
teeth,  in  that  the  teeth  are  strengthened  by  the  pink  vulcanite,  and  all 
spaces  and  interspaces  favorable  to  the  lodgement  of  food-debris  are  com- 
pletely filled  by  the  vulcanite,  thereby  rendering  the  denture  clean  and 
much  more  agreeable  to  the  wearer. 

The  plan  of  procedure  is  to  mount  the  plain  teeth  on  a  gold  or 
platinum  plate,  back,  solder,  and  finish  them.  Wax  is  then  built  on  the 
plate  from  the  labial  and  buccal  edges  to  the  necks  of  the  plain  teeth, 


VULCANITE  REGULATING  APPLIANCES. 


541 


and  carefully  modelled  to  imitate  irregularities  of  the  natural  gums.  It 
is  then  to  be  invested  in  the  first  half  of  a  vulcanite  flask,  with  the  cut- 
ting edges  of  the  teeth  downward,  the  plaster  being  allowed  to  cover  the 
entire  plate,  the  only  part  of  the  denture  exposed  being  the  wax  at  the 
rim  edge  of  the  plate ;  and  only  enough  of  the  wax  at  that  point  need 
be  exposed  to  allow  access  in  packing  the  rubber  around  the  teeth.  The 
second  half  of  the  flask  is  then  adjusted  and  filled  with  plaster  when  the 
flashing  is  complete  :  after  the  flask  is  opened  and  the  wax  removed  by 
washing  out  with  a  stream  of  boiling  water,  the  pink  rubber  is  cut  into 
narrow  strips,  softened  by  gentle  heat,  and  carefully  packed  into  the 
vacancy  left  by  the  wax.  This  packing  must  be  done  with  the  utmost 
care,  in  order  that  all  spaces  may  be  thoroughly  filled  with  rubber.  When 
quite  full  a  slight  excess  of  rubber  should  be  added  to  ensure  sufficient 
pressure  to  thoroughly  distribute  the  rubber.  It  may  then  be  vulcanized 
and  finished,  as  described  in  another  part  of  this  chapter.  Ordinary 
pink  vulcanite  requires  exposure  in  alcohol  to  solar  rays  to  fully  develop 
the  pink  tint.  The  Walker  granular  gum,  which  is  stronger  than  the 
ordinary  pink  rubber,  may  be  employed. 

Vulcanite  Regulating  Appliances. — Although  the  vulcanite  regu- 
lating plate  has  to  a  great  extent  given  place  to  appliances  constructed 
of  metal  after  the  Farrar,  Angle  and  Patrick  systems,  yet  cases  will  con- 
stantly arise  where  fixtures  constructed  of  vulcanite  alone  or  in  combina- 
tion with  gold  will  be  found  to  be  almost  indispensable  in  the  treatment 
and  retention  of  irregularities  of  the  teeth.  It  would  be  impossible  to 
give  in  these  pages  a  complete  classification  of  the  almost  limitless  va- 
riety of  regulating  appliances  formed  of  vulcanite.  A  few  models  have 
therefore  been  selected  to  represent  some  of  the 
most  practical  and  useful  forms.  Figs.  211,  212 
and  213  are  typical  regulating  plates  of  the 
system  devised  for  the  upper  and  lower  jaws 
by  Walter  H.  Coffin,  F.  C.  S.,  F.  R.  M.  S.,  M. 
Phys.  S.  of  London,  England.  The  wire  in 
Fig.  213  shows  the  form  best  adapted  for  ex- 
panding the  anterior  portion  of  the  arch  ;  that 
in  Fig.  211,  the  form  adapted  to  enlarging 
the  posterior  portion.  The  additional  wire  on 
the  left  of  Fig.  211  is  intended  to  force  a 
lateral  incisor  outward,  while  the  W-shaped 
piece  expands  the  arch  to  allow  room  for  the 
lateral  to  assume  its  proper  place  in  relation  to 
the  neighboring  teeth.  It  is  assumed  in  this 
system  of  regulating  that  all  irregularities  of 
the  teeth  require  for  their  correction  the 
spreading  of  the  arch,  and  it  is  for  this  pur- 
pose that  the  split  plate  and  piano  wire  in  the 
shape  shown  in  the  figure  are  used,  and  indi- 
vidual teeth  to  be  moved  or  rotated  are  acted 
upon  by  other  wires  fastened  in  the  plate  in 
such    positions    as    may    be    required.^       "  The   eifectiveness    of    the 

1  From  Dr.  H.  J.  McKellop's  paper,  published  in  vol.  xxiv.  pp.  477-479  of  Dental 
Cosmos. 


Fig.  661. 


542     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

Coffin  appliance  depends  upon  the  elasticity  of  a  piece  of  piano  wire, 
and  if  all  the  details  of  the  construction  and  application  of  an 
appliance  after  the  Coffin  method  have  been  carefully  executed, 
the  patient  may  be  safely  entrusted  with  its  subsequent  manage- 
ment. The  impression  in  this,  as  in  the  preparation  of  all  other  forms 
of  regulating  apparatus,  should  be  taken  in  plaster.  The  length  of 
wire  required  is  from  1  inch  to  3 J  inches  in  ordinary  cases.  In  the 
construction  of  the  Coffin  apparatus  two  pairs  of  pliers  and  a  pair  of  clasp- 
benders  are  used  (Figs.  661  to  663).     The  jaws  of  the  largest  of  the 


Fig.  663. 


Fig.  662. 


pliers  (Fig.  661)  are  provided  with  a  wire-cutting  side  for  cutting  the 
wire  into  the  proper  length  and  also  to  bend  it  to  the  required  shape. 
After  the  wire  is  cut  off  with  the  large  pliers  it  is  bent  first  in  the 
centre,  then  back  on  each  side  with  the  clasp-benders  (Fig,  663),  holding 
it  with  the  pliers.     Care  must  be  taken  to  avoid  getting  any  twists  in 


the  wire  and  to  make  the  curves  smooth  and  even.  It  is  then  put  into 
shape  to  occupy  its  proper  place  when  attached  to  the  plate  by  adjusting 
it  with  the  fingers  and  the  pliers,  after  which  the  ends  to  be  secured  in 


VULCANITE  REGULATING  APPLIANCES.  543 

the  rubber  are  bent  at  a  sharp  angle,  so  as  to  raise  the  part  which  pro- 
jects from  the  plate,  and  flattened  with  a  hammer  :  no  part  of  the  wire 
should  be  heated.  The  appearance  of  a  wire  ready  for  use  is  shown  in 
Fig.  210.  The  ends  of  the  wire  are  then  tinned,  a  small  copper  cup 
filled  with  molten  tin  (Fig.  664),  which  rests  on  a  tripod,  being  used  for 
the  purpose.  Some  operators  coat  the  whole  surface  of  the  wire  with  tin 
to  prevent  oxidation,  but  this  is  not  absolutely  necessary,  as  in  most 
mouths  the  surface  of  the  wire  exposed  to  the  oral  fluids  does  not  suffer 
to  an  extent  beyond  mere  dislocation. 

In  speaking  of  the  construction  of  these  appliances  Mr.  Coflin  ^  says  : 
^'  The  perfection  of  the  model  must  be  insisted  upon,  as  an  entire  plate 
may  fit  well  and  securely,  and  yet  both  of  its  halves  be  so  loose  when 
divided  as  to  be  useless  ;  while,  on  the  other  hand,  the  halves  of  a  split 
plate  may  be  early  fitted  which  before  division  could  not  possibly  be 
inserted."  Mr.  Coflin  recommends  gutta-percha  as  the  best  material 
with  which  to  obtain  impressions,  on  account  of  its  slight  contraction  in 
cooling,  which  affords  shrinkage  enough  to  ensure  the  thin  hard-rubber 
copy  fitting  tightly.  As  a  rule,  gutta-percha  is  unreliable  as  an  impres- 
sion material,  and  the  author  believes  that  a  perfect  plaster  impression 
will  always  afford  the  most  satisfactory  results. 

Fig.  665  illustrates  a  regulating  apparatus  formed  of  vulcanite  cov- 
ering the  deciduous  and  first  permanent  molars,  arranged  with  a  gold 
T-piece,  which  is  provided  with  a  threaded  end  and  a  nut  for  the  pur- 

FiG.  665.  Fig.  666. 


T-pins  with  nut  to  draw  in  protruding  centrals,     Shows  gold  hooks  for  retaining  lateral  incisor 


pose  of  gradually  increasing  pressure  upon  the  projecting  teeth  and 
drawing  them  into  proper  position.  This  plate  may  also  be  worn  as  a 
retaining  plate  to  hold  the  teeth  in  position  until  they  become  perma- 
nently fixed. 

Fig.  QQQ  shows  a  vulcanite  retaining  plate  designed  to  hold  in  posi- 
tion the  lateral  incisors,  which  have  been  drawn  into  correct  position  by 
means  of  rubber  ligatures  attached  to  a  gold  button  in  the  palatal  por- 
tion of  the  plate,  as  seen  in  Fig.  667.  The  hooks  at  A  are  of  gold  with 
perforated  ends  imbedded  in  the  vulcanite.  The  half-clasps  or  stays  at 
B  are  intended  to  rest  against  the  second  deciduous  molars. 

It  is  always  difficult  to  secure  a  plate  by  contact  with  the  temporary 
teeth,  owing  to  their  tapering  forms.  It  is  therefore  necessary,  where 
efforts  are  being  made  to  correct  irregularities  in  very  young  mouths,  to 
^  Dental  Comnos,  vol.  xxiv.  p.  466. 


544    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

secure  them  by  means  of  gold  clasps  or  stays.  These  should  be  made  to 
extend  somewhat  under  the  free  margin  of  the  gums,  so  as  to  embrace 
the  most  prominent  part  of  the  teeth  thus ;  and  to  accomplish  this  the 
model  should  be  carved  away  at  the  margin  of  the  gum,  as  shown  in 
Fig.  666,  in  order  that  the  clasp  or  stay  may  be  fitted  to  the  part  of  the 
tooth  indicated. 

Fig.  668  illustrates  a  vulcanite  plate  to  be  applied  to  cases  where  the 
central  incisors  require  forcing  outward,  while  the  projecting  laterals  are 

Fig.  667.  Fig.  668. 


Retaining  plate  No.  8.  To  force  out  centrals  by  means  of  screws  and  at  the 

same  time  to  draw  in  laterals  by  means  of  rubber. 

to  be  drawn  in  until  they  line  with  the  cuspids.  This  plate  is  made  to 
cover  the  lingual  surfaces  of  the  centrals  to  their  cutting  edges.  The 
portion  immediately  back  of  the  central  teeth  should  be  at  least  an 
eighth  of  an  inch  in  thickness.  As  the  means  of  forcing  out  the  front 
teeth  consists  of  gold  screws  held  in  the  rubber,  it  is  therefore  necessary 
that  the  material  at  that  point  should  be  of  sufficient  thickness  to  afford 
a  secure  hold.  The  plate  is  constructed  so  as  to  cover  the  bicuspids  and 
first  molars,  partly  for  the  sake  of  security  and  partly  because  the  force 
of  occlusion  assists  in  forcing  out  the  centrals.  When  the  plate  is 
ready  for  adjustment  holes  are  drilled  in  the  vulcanite  back  of  the  cen- 
tral teeth,  and  stout  gold  screws  of  the  thickness  of  No.  17  or  18  are 
screwed  into  the  vulcanite.  It  is  not  necessary  to  cut  a  thread  in  the 
rubber ;  the  gold  screw  will  force  a  thread  without  previous  tapping. 
The  screw  should  project  at  the  point  of  contact  with  the  lingual  sur- 
faces of  the  centrals,  at  first  about  the  twentieth  of  an  inch,  and  every 
day  or  two  the  screw  may  be  lengthened  by  grasping  it  with  the  pliers 
and  by  a  turn  or  two  increasing  the  stress  upon  the  teeth.  The  lateral 
teeth  may  be  brought  into  correct  position  at  the  same  time  by  attach- 
ing two  rubber  rings  cut  from  a  piece  of  French  rubber  tubing  and  tied 
with  a  strong  linen  thread  to  the  gold  button  ^  of  Fig.  668,  and  then 
stretched  out  so  as  to  engage  the  lateral  teeth.  When  rubber  ligatures 
are  employed  in  connection  with  vulcanite  plates,  provision  should  be 
made  to  prevent  the  ligature  from  resting  upon  and  irritating  the  tissues 
between  the  lingual  surfaces  of  the  teeth  and  the  edge  of  the  plate.  It 
is  sometimes  necessary  to  attach  a  supplementary  piece  to  the  plate  at 
the  point  indicated,  to  keep  the  ligatures  from  injuring  the  gum  (Fig. 
669).  The  gum  is  very  liable  to  thicken  up  as  the  protruding  teeth  are 
drawn  inward. 


VULCANITE  REGULATING  APPLIANCES. 


545 


The  screw  (Fig.  670)  may  be  used  in  connection  with  the  T-piece 
(Fig,  665)  in  rotating  a  single  central  tooth  by  applying  the  force  at 
opposite  points  on  the  tooth,  and  this  is  done  by  lengthening  the  screw. 


Fig.  669. 


Fig.  670. 


Bridge  added  to  plate  by  riveting  to  relieve 
pressure  of  rubber  ligatures. 


To  force  out  centrals. 


Kingsiey's  slotted  vulcanite  plate,  with  jack-screw,  shown  by  Figs. 
671-673,  is  another  example  of  the  value  of  vulcanite  in  the  formation 
of  regulating  appliances.     Fig.  671  is  designed  to  move  outward  a  left 


Fig.  671. 


superior  second  bicuspid  ;  Fig.  672,  to  move  outward  both  inferior 
bicuspids  of  the  left  side,  the  first  more  than  the  second ;  Fig.  673  was 
intended  to  operate  upon  all  four  of  the  inferior  bicuspids. 


Fig.  672. 


Fig.  673. 


Kingsley's  slotted  vulcanite  plates  with  jack-screw. 


One  of  the  most  effective  vulcanite  regulating  appliances  was  devised 
by  Dr.  Louis  Jack  (Fig.  674)  for  the  treatment  of  excessive  protrusion 

35 


546     VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

of  the  superior  incisors  and  cuspids,  so  frequently  met  with,  and  which  is 
variously  attributed  to  the  habit  of  thumb-sucking,  unusual  shortness  of 
bicuspids  and  molars,  absence  of  normal  power  in  the  orbicularis  oris  mus- 
cle, etc.  (See  Fig.  674.)  It  consists  of  a  strong  gold  bar  passing  around 
the  labial  surfaces  of  the  incisors,  attached  to  vulcanite  caps  fitting  over 
the  bicuspids  and  first  molar  on  each  side.    As  will  be  seen  in  the  illus- 

FiG.  674. 


tration,  the  caps  are  formed  of  gold  on  the  masticating  surfaces,  so  that 
the  caps  will  not  be  broken  by  the  forcible  closure  of  the  lower  teeth. 
On  the  outside  of  the  right  cap  is  a  threaded  cylinder,  into  which  fits  a 
stout  screw  at  the  end  of  the  gold  bar :  stress  is  brought  to  bear  upon 
the  front  teeth  by  simply  giving  the  right  cap  a  turn  or  two,  which 
shortens  the  bar.  The  gold  portion  of  the  appliance  is  imbedded  in 
vulcanite  in  order  to  secure  accuracy  of  adaptation  of  the  caps  to  the 
teeth.  This  appliance  is  particularly  effective  in  those  cases  where  it  is 
necessary  to  obtain  room  by  the  extraction  of  the  right  and  left  first 
bicuspids.  The  spaces  left  by  the  removal  of  the  teeth  are  very 
quickly  closed  by  the  gradual  force  apjDlied  by  this  apparatus,  and  the 
six  anterior  teeth  are  drawn  bodily  into  correct  position. 

The  same  appliance  may  be  satisfactorily  used  to  move  outward  the 
lower  anterior  teeth  by  arranging  the  bar  so  that  force  may  be  exerted 
against  the  lingual  surface  of  the  teeth. 

After  the  proper  position  of  the  teeth  has  been  secured  the  appliance 
is  to  be  worn  for  several  months  as  a  retaining  fixture.  In  constructing 
this  appliance  the  first  step  is  to  place  softened  sheet  wax  upon  the 
crowns  of  the  teeth  to  be  embraced  by  the  caps :  this  is  pressed  with  the 
thumb  to  complete  contact  with  the  plaster  teeth ;  a  zinc  die  and  lead 
counter-die  are  then  secured,  and  the  platinum  gold  plate  swaged  to 
cover  the  crowns  of  the  teeth  over  the  wax.  The  bar  is  soldered  to  the 
left-hand  cap,  and  the  threaded  cylinder  to  the  other.  The  gold  caps 
with  the  bar  attached  are  then  placed  upon  the  model.  The  wax  pre- 
viously placed  upon  the  masticating  surfaces  of  bicuspids  and  molars 
will  raise  the  caps  sufficiently  from  the  plaster  teeth  to  allow  an  equal 
thickness  of  vulcanite  to  interpose  between  the  gold  and  the  teeth. 
Additional  wax  is  added  to  finish  out  the  caps  to  the  desired  dimen- 
sions. The  piece  is  then  flasked,  packed,  and  vulcanized.  By  this 
combination  strength  is  secured  by  the  use  of  the  gold  plate  upon  the 


INTERDENTAL  SPLINTS. 


547 


masticating  surfaces,  while  closeness  of  adaptation  is  obtained  by  the 
vulcanite. 

In  flasking  the  piece  it  should  be  arranged  so  that  the  fixture  remains 
in  the  second  half  of  the  flask,  the  first  half  holding  the  plaster  model 
only.  The  best  way  to  accomplish  this  is  to  cut  away  all  the  plaster 
teeth  from  the  model  anterior  to  those  embraced  by  the  caps ;  when 
removed  to  the  margins  of  the  gums  the  bar  is  free  to  be  enveloped 
by  the  plaster  investment  when  flasking,  and  when  the  flask  is  opened 
preparatory  to  packing  the  only  part  exposed  will  be  the  gold  plate  which 
forms  the  tops  of  the  caps,  while  in  the  first  half  of  the  flask  the  teeth 
to  be  covered  will  alone  be  visible. 

Interdental  Splints. 

Interdental  splints  in  conjunction  with  submental  compresses  and 
occipito-mental  bandages  have  been  used  by  surgeons  in  the  treatment 
of  fractured  jaws  since  1780.  p^^  g^^^ 

Drs.  F.  B.  Gunning  of  New  York  and 
J.  B.  Bean  of  Atlanta,  Georgia,  were  the 
first  to  describe  methods  of  constructing 
interdental  splints  of  vulcanized  rubber. 
Both  of  these  gentlemen  claimed  priority,  and 
it  appears  that  the  invention  was  made  and 
published  independently  by  each  at  about  the 
same  period. 

The   interdental   splints  of  Drs.   Gunning 
and  Bean  were    similar,   except   that  the  ar- 
rangement   of    the    submental     compress     and         Gunning  interdental  splint. 
bandage  of  Dr.  Bean  differed  materially  from  that  used  by  Dr.  Gunning. 

The  Gunning  splint  (Fig.  675)  covered  both  the  upper  and  lower 
teeth,  and  was  provided  with  an  opening  in  front  for  the  reception  of 
food,  a  bandage  over  the  head  being  used 
as  a  means  of  securing  adjustment  of  the 
lower  jaw  with  the  splint.  Other  splints 
were  used  by  Dr.  Gunning  which  covered 
the  lower  teeth  only,  leaving  the  motions 
of  the  jaw  free.  Fig.  676  shows  the 
arrangement  of  the  mental  compress  and 
bandages  employed  by  Dr.  Bean  to  main- 
tain the  relation  of  the  jaws. 

The  preliminary  steps  in  the  treatment 
of  fractures  of  the  jaw  are  generally  made 
more  or  less  difficult  by  the  pain  and 
swelling  incident  to  the  injury.  For  the 
impression,  plaster  of  Paris  is  by  far  the 
most  suitable  material,  as  it  necessitates 
less  bulk  and  may  be  applied  with  much 
less  force  than  is  required  to  press  wax  or 
modelling  compound  to  complete  contact 
with  the  teeth.  If  plaster  of  Paris  be 
intelligently  and  skilfully  employed  in  these  cases,  no  violence  need 
be  used  either  in  its  application  or  removal.      An   impression-cup  of 


Fig.  676. 


548     VULCANIZED  RUBBER,  BASE  FOR  •ARTIFICIAL  DENTURES. 


Fig.  677. 


the  proper  size,  with  a  smooth  and  polished  surface,  should  be  selected 
and  oiled  to  ensure  its  easy  separation  from  the  plaster  when  hard.  The 
latter  should  be  of  the  finely-ground  variety,  such  as  is  furnished  by  the 
dental  depots  for  impression  purposes,  and  which  hardens  quickly, 
breaks  with  a  sharp  fracture,  and  requires  but  little  force  in  its  removal. 
The  cup,  filled  sufficiently  with  plaster,  is  applied  while  the  latter  is 
still  quite  soft,  and  held  until  it  sets.  The  cup  is  then  separated  from 
the  plaster  with  scarcely  any  force ;  the  plaster  impression  is  gently 
removed  in  pieces  from  around  the  teeth,  and  placed  in  their  proper 
relation  to  each  other  in  the  cup.  If  any  of  the  teeth  have  been  loosened 
by  the  injury  to  the  jaw,  the  use  of  plaster  of  Paris  is  especially  indicated 
in  order  to  avoid  their  displacement  by  the  downward  pressure  of  wax 
or  modelling  compound. 

If  the  fracture  be  of  a  complicated  nature  and  accompanied  with  con- 
siderable displacement  of  the  parts,  as  shown  in  Fig.  677,  no  persistent 

effort  need  be  made  to  restore  the  de- 
ranged fragments,  as  that  part  of  the 
operation  can  be  just  as  well  accom- 
plished on  the  plaster  model,  the  pa- 
tient being  thus  relieved  from  the 
additional  suffering  which  would  be 
sure  to  attend  any  attempt  to  set  the 
broken  parts  of  the  jaw. 

An  impression  is  then  taken  of  the 
upper  teeth,  the  positions  of  which, 
even  when  the  superior  maxilla  is 
broken,  are  not  likely  to  be  changed. 
When  the  models  have  been  obtained 
cuts  may  be  made  with  a  fine  saw 
through  the  model  of  the  lower  jaw  at  points  corresponding  with  the  frac- 
tures, and  the  articulation  corrected  by  adjustment  to  the  upper  teeth, 
which  will  serve  the  operator  as  infallible  guides.  The  parts  of  the 
lower  model  are  then  secured  in  their  corrected  relation  by  additional 
plaster :  no  effort  need  be  made  to  set  the  jaw  after  the  impression  is 
taken  until  the  splint  is  ready  for  adjustment. 

To  preserve  the  proper  relation  of  the  lower  to  the  upper  teeth,  the 
models  should  be  placed  in  an  articulator  (Fig.  678). 

The  set  screw  of  the  articulator  should  be  arranged  so  as  to  allow  of 
a  separation  between  the  upper  and  lower  teeth  of  about  a  quarter  of  an 
inch.  "While  it  is  desirable  that  the  splint  when  finished  should  fit  the 
teeth  and  gums  with  sufficient  closeness  to  enable  it  to  serve  the  purpose 
for  which  it  is  designed,  it  must  be  borne  in  mind  that  to  save  the 
patient  from  additional  pain  in  its  adjustment  it  is  necessary  that  the 
fixture  should  go  immediately  to  its  place,  without  delay  or  repeated 
trials.  To  accomplish  this,  the  plaster  teeth  and  gums  for  about  a 
quarter  of  an  inch  above  the  necks  should  be  carefully  covered  with  No. 
60  tin-foil,  for  the  purpose  of  slightly  enlarging  the  splint  and  to  secure 
a  smooth  surface  to  the  inside  of  it.  Interdental  dovetail  spaces  may  be 
arranged  by  filling  the  undercuts  with  plaster  before  applying  the  foil, 
or  by  trimming  away  retaining  points  in  the  finished  piece  with  a  sharp 
knife-blade  or  engine  bur,  so  that  the  splint  may  be  applied  or  removed 


INTERDENTAL  SPLINTS.  549 

without  much  force.     The  splints  are  then  formed  on  the  plaster  models 
of  thin  sheet  wax  of  a  uniform  thickness  slightly  in  excess  of  a  sixteenth 

Fig.  678. 


of  an  inch  :  wax  of  a  sufficient  thickness  is  then  placed  between  for  the 
purpose  of  uniting  them,  as  shown  by  Fig.  679. 


Fig.  679. 


The  upper  and  lower  splints  are  to  be  carefully  united  and  made  per- 
fectly smooth  by  means  of  a  hot  spatula. 

The  wax  splint  is  next  to  be  removed  from  the  models  and  invested 
in  a  suitable  flask  in  the  usual  way.  The  models  may  be  removed  from 
the  articulator  for  the  purpose  of  vulcanizing  upon  them  ;  this,  however, 
is  not  really  necessary.     It  is,  indeed,  a  better  plan  to  preserve  the 


550    VULCANIZED  RUBBER,  BASE  FOR  ARTIFICIAL  DENTURES. 

models  and  articulation  to  assist  in  the  preparation  of  the  finished  splint 
for  final  adjustment.  Much  the  better  way  is  to  carefully  fill  the  deep 
parts  of  the  wax  splint  with  plaster  by  means  of  a  camel's-hair  brush, 
and  then  invest  with  the  line  of  division  at  about  the  middle,  as  shown 
by  the  dotted  line  in  Fig.  680. 


.^Vs<<^^<Kxv<vs^V^^^^V^^^'v^^^<!^:^^ 


The  tin-foil  should  extend  about  an  eighth  of  an  inch  beyond  the 
wax ;  it  will  thus  be  held  securely  by  the  investment,  and  disarrange- 
ment when  the  flask  is  separated  for  the  removal  of  the  wax  will  be 
avoided. 

A  sectional  view  of  the  flask  with  the  invested  splint  is  given  in  Fig. 
680.  The  flask  is  shown  by  F ;  the  models  by  31;  the  plaster  invest- 
ment by  P;  tin-foil  covering  the  teeth  with  extension  beyond  the  wax 
splint  by  T;  the  wax  pattern  of  splint  by  W. 

The  same  precautions  recommended  for  the  waxing,  flasking,  and 
packing  of  ordinary  vulcanite  dentures  should  be  observed  in  the  con- 
struction of  splints,  but  especial  care  should  be  observed  in  the  separa- 
tion of  the  flask  to  avoid  breaking  the  thin  plaster  teeth,  as  such  an 
accident  would  greatly  embarrass  the  subsequent  steps  of  the  operation. 

The  flask  should  therefore,  previous  to  any  attempt  to  separate  it,  be 
placed  in  hot  water,  and  allowed  to  remain  until  the  w^ax  is  quite  soft. 
After  the  separation  the  last  particle  of  wax  should  be  washed  away  by 
means  of  a  stream  of  boiling  water. 

The  packing  of  the  rubber  demands  more  than  ordinary  care  to 
ensure  its  being  carried  into  the  deep  and  narrow  spaces  around  the 
teeth.  The  rubber  should  be  cut  into  thin  strips,  softened  over  boiling 
water,  and  carried  into  the  matrix  by  a  suitable  instrument,  such  as  an 
old  plugger.  There  should,  of  course,  be  a  slight  excess  of  rubber.  The 
vents  may  be  as  for  ordinary  dentures. 

Interdental  splints  need  not  be  thicker  than  is  consistent  with  suf- 
ficient strength.  They  should  be  well  finished,  and  provided,  when 
admissible,  with  a  front  opening,  as  shown  in  Fig.  679,  large  enough  for 
the  passage  of  a  feeding-tube. 

An  interdental  splint  cannot  usually  be  relied  upon  to  immova- 
bly retain  the  broken  jaw  without  the  assistance  of  bandages,  screws, 


INTERDENTAL  SPLINTS. 


551 


wires,  or  ligatures.  Fig.  681  (Kingsley's  Oral  Deformities)  shows  the 
use  of  screws  passed  through  the  splint  at  points  between  the  cervical 
portions  of  the  crowns  of  the  molar  teeth. 


Fig.  681. 


Fig.   682    {ibid.)    illustrates  a  splint  provided   with   arms   of  steel 
wire  one-eighth  of  an  inch  in  diameter,  arranged  to  come  "  out  of  the 


mouth  when  the  splint  is  in  position,  passing  back  along  the  cheek 
on  a  line  with  the  teeth."  This  splint  was  invented  by  Dr.  Norman 
W.  Kingsley,  and  the  description  of  it,  with  the  illustration,  is  from  his 
valuable  work  on  Oral  Deformities.  Fig.  682  shows  the  splint  in  posi- 
tion and  the  submental  compress  attached  to  the  side-bars. 


552     VULCANIZED  RUBBER,   BASE  FOR  ARTIFICIAL  DENTURES. 

It  will  be  seen  that  this  splint  covers  the  lower  teeth  only,  and  that 
its  top  occludes  with  the  upper  teeth  to  admit  of  mastication.  The  con- 
struction of  such  a  splint  is  accomplished  by  placing  upper  and  lower 
models  in  an  articulator,  forming  the  wax  splint  as  before  described, 
arranging  the  occlusion  so  that  contact  of  the  upper  teeth  will  be  uni- 
form, imbedding  two  stout  steel  wires  with  flattened  ends  in  the  wax,  so 
that  they  will  bear  the  strain  which  will  be  required  of  them  while  the 
splint  is  in  position.     Fig.  683  shows  the  waxed  splint  with  side-bars  in 

Fig.  683. 


the  articulator  ready  for  investment.  The  particular  flask  best  adapted 
for  the  vulcanizing  of  interdental  splints  is  oblong  in  form,  and  is  larger 
than  ordinary  vulcanite  flasks ;  it  is  known  as  the  "  box  flask. '^ 


CHAPTER  XYI. 

CELLULOID  AND  ZYLONITE. 

By  W.  W.  Evans,  M.  B.,  D.  D.  S. 


Celluloid  and  Zylonite — a  distinction  without  a  difference.  In 
these  two  materials — alike  and  yet  not  alike — we  have  a  compound  from 
which  are  made  dental  base-plates  as  well  as  numerous  other  articles. 
This  compound  will  supply  many  requirements  which  no  other  sub- 
stance now  known  to  the  profession  fills.  Yet  it  is  but  little  under- 
stood, and  there  are  many  drawbacks  to  its  wide  use. 

History. — Pelouze,  with  a  genius  for  discoveries,  found  that  paper 
treated  with  concentrated  nitric  acid  instead  of  being  decomposed 
retained  its  form,  assuming  a  parchment-like  appearance  and  flashing 
into  vapor  when  brought  into  contact  with  flame. 

Jacobi  of  St.  Petersburg,  experimenting  with  ozone  and  observing 
the  passivity  of  iron  in  concentrated  acids,  was  induced  to  try  the  effect 
of  these  acids  on  organic  matters.  As  a  result  he  patented  the  discovery 
of  gun-cotton.  This  was  in  1847.  Jacobi  had  simply  followed  in  the 
footsteps  of  Pelouze  :  the  second  discovery  was  in  no  wise  greater  than 
the  first. 

Baron  Lenz  of  Austria  brought  the  gun-cotton  discovery  of  Jacobi 
into  practical  use.  The  Austrian  government  later  on  carried  it  to  a 
more  perfect  state. 

Abel  of  England  also  made  valuable  improvements  in  the  process  of 
manufacture,  and,  it  was  reported,  sold  his  patents  to  Messrs.  Prentice, 
gunpowder  manufacturers,  for  forty  thousand  pounds  sterling.  They, 
having  a  large  fire  in  their  factories  at  Waltham-on-Thames,  met  with 
sad  loss  of  life  from  explosion  of  the  gun-cotton,  which  they  were  under 
the  impression  was  not  explosive.  This  was  a  deathblow  to  its  manu- 
facture for  several  years.  In  the  mean  time  the  manufacture  of  nitro- 
glycerin had  made  great  progress. 

Hadon,  after  a  minute  examination  of  cellulose  as  manufactured  for 
surgical  purposes,  found  that  in  some  hands  it  was  frequently  a  failure. 
This  led  him  to  the  inference  that  there  were  several  preparations  of  nitro- 
cellulose, instead  of  simply  a  more  or  less  perfect  "gun-cotton."  He 
found  that  cellulose  could  be  converted  into  three  products  by  means  of 
nitric  acid  diffused  in  sulphuric  acid  of  varying  strengths,  thus  modify- 
ing its  action.  These  three  products  chemists  usually  designate  under 
the  generic  name  of  pyroxylins.  They  are  all  nitric  ethers  of  cellulose. 
They  are  mononitro-cellulose,  dinitro-cellulose,  trinitro-cellulose.^ 

^  The  dinitro-cellulose  or  pyroxylin  of  the  U.  S.  P.  is  made  by  macerating  for  fifteen 
hours  half  a  troy-ounce  of  cotton  in  a  mixture  of  four  troy-ounces  of  sulphuric  acid 

653 


554  CELLULOID  AND  ZYLONITE. 

The  manufacture  of  the  dinitro- cellulose  must  be  a  very  delicate 
operation,  as  the  following  quotations  from  some  notes  furnished  me  will 
show  :  "  Temperature  of  combination,  absence  of  water  (hygroscopic)  in 
the  paper  or  cotton,  state  of  division,  concentration  more  or  less  of  the 
acid — J  of  1  per  cent,  of  water  being  capable  of  producing  a  totally 
different  product — render  the  manufacture  of  the  dinitro-cellulose  a  very 
nice  operation,  to  that  extent  that  two  years  ago  experts  who  manufac- 
tured these  products  for  photographic  purposes  asserted  that  it  seemed 
impossible  to  prepare  two  samples  exactly  alike. 

"  On  the  one  hand,  dry  weather  and  very  concentrated  nitric  acid 
render  the  product  hard — i.  e.  insoluble  in  the  test-liquor  of  1  part  cam- 
phor and  20  parts  alcohol — and,  on  the  other  hand,  weakening  acids  by 
absorption  of  water  from  the  atmosphere  alone  produces  zyloidin  or 
mononitro-celluloid,  soluble  in  the  acids,  and,  instead  of  the  average  40 
per  cent,  increase,  the  manufacturer  finds  an  increase  of  only  18  per 
cent,  and  a  tendency  to  rapid  change.  It  requires  the  knowledge  and 
skill  of  a  very  observant  operative  to  remedy  these  defects,  and  without 
correct  conceptions  of  the  possible  causes  of  these  changes  he  is  very 
apt  to  despair." 

The  extreme  tenacity  of  the  film  of  collodion,  it  being  a  colorless 
transparent  material  not  aifected  by  moisture,  suggested  its  application 
as  a  factor  in  the  arts,  but  the  cost  of  its  solvent — namely,  2  parts  ether 
and  1  part  alcohol,  both  lost  by  evaporation — was  prohibitory. 

It  is  said  that  an  Englishman  named  Parkes  made  the  first  celluloid 
in  1855,  calling  it  parkesite,  zylonite,  etc.  D.  Spill  also  claims  the  dis- 
covery that  a  solution  of  camphor  in  alcohol  dissolved  collodion,  on  the 
strength  of  which  he  took  out  patents.  It  was  afterward  found  that 
wood  alcohol  was  also  a  solvent. 

But  the  first  practical  knowledge  which  we  have  of  the  material  was 
in  1869.  Under  the  management  of  Mr.  J.  Smith  Hyatt  the  Newark 
Celluloid  Manufacturing  Company  was  organized  :  this  company  spent 
large  sums  of  money  in  experimenting  and  perfecting  the  process  of 
manufacture ;  they  met  with  accidents  and  disappointments  at  first,  but 
were  finally  successful  in  their  efforts. 

and  three  and  a  half  troy-ounces  of  nitric  acid,  afterward  washing  the  cotton  repeatedly 
until  all  free  acid  is  removed,  and  then  drying  by  means  of  a  water-bath. 

The  action  of  nitric  acid  in  the  formation  of  each  of  the  nitro-cellulin  compounds  is. 
represented  in  the  following  equations  from  Attfield's  Chemistry  (p.  398) : 

CeHjoOs  +  HNO3  =  Ce  {  ^5^  }  O5  +  H,0. 

Cellulin.    Nitric  acid.     Mononitro-         Water, 
eellulin. 

CeH,o05  +  2HNO3  =  Ce  {IIq  J  O5 -f  2H  A 
Cellulin.    Nitric  acid.    Dinitro-cellulin.      Water. 

CeH,o05  +  3HNO3  =  Ce  {  fj^Q  J  O5  +  3H A 

Cellulin.    Nitric  acid.    Trinitro-cellulin.    Water. 

As  seen  in  the  equations,  one,  two,  and  three  molecules  of  peroxide  of  nitrogen,  NO2,  are 
substituted  for  one,  two,  and  three  atoms  of  hydrogen  respectively,  one,  two,  and  three 
molecules  of  water  being  severally  formed  in  the  reaction.  The  purpose  of  the  admix- 
ture of  sulphuric  acid  with  the  nitric  acid  is  to  free  the  latter  from  the  presence  of  the 
water  formed,  sulphuric  acid  through  its  affinity  for  that  fluid  readily  taking  it  up.  _  Of 
these  three  nitro-cellulin  compounds,  the  dinitro-cellulin  is  the  only  one  soluble  in  a 
mixture  of  alcohol  and  ether,  this  solution  forming  the  collodion  of  commerce. 


THE  MANUFACTURE  OF  CELLULOID.  555 

The  American  Zylonite  Company  is  justly  noted  for  the  beauty,  uni- 
formity, and  strength  of  the  material  it  produces. 

As  now  manufactured,  celluloid  is  composed  of  pyroxylin,  camphor, 
oxide  of  zinc,  and  vermilion,  in  the  proportions  of  about  100  parts  of 
pyroxylin,  40  of  camphor,  2  of  oxide  of  zinc,  and  .06  of  vermilion.  A 
very  good  description  of  the  process  of  manufacture  of  the  article  and 
of  its  more  important  properties  will  be  found  in  an  extract  from  the 
Ameriean  Artisan,  given  in  the  Denial  Cosmos  for  January,  1875,  extracts 
from  which  are  quoted  below,  although  the  opinion  therein  expressed, 
that  the  celluloid  is  a  chemical  combination  of  the  constituents  named 
above,  is  not  generally  accepted,  as  far  as  dental  blanks  are  concerned, 
for  certain  recent  experiments  with  the  microscope  have  led  to  the  belief 
that  it  is  simply  a  mechanical  admixture.     It  says  : 

"After  the  pulp  is  ground  in  the  beater-engine,  and  the  camphor  and 
whatever  coloring  material  may  be  desired  are  thoroughly  incorporated 
with  it,  the  substance  being  kept  meanwhile  at  the  proper  temperature, 
the  superfluous  water  is  removed  by  pressure  and  absorption,  a  peculiar 
porous  material  made  specially  for  the  latter  purpose  being  employed. 

"  During  the  process  of  drying  under  pressure  and  absorption  the 
material  becomes  transformed,  so  that  it  is  no  longer  nitro-cellulose, 
but  imperfect  celluloid.  In  so  far  as  conversion  has  taken  place,  its 
properties  have  undergone  a  total  change.  All  that  remains  to  convert 
it  into  the  various  articles  referred  to  is  manipulation  under  heat  and 
pressure,  during  which  process  the  chemical  combination  is  completed. 

"  For  some  qualities  of  the  material,  desired  to  be  produced,  a  small 
percentage  of  alcohol  is  added  in  the  subsequent  manipulation.  As 
evidence  that  there  is  a  perfect  chemical  combination,  and  not  a 
mere  mechanical  mixture  of  the  materials,  it  may  be  stated  that 
whereas  camphor  in  its  uncombined  state  is  an  extremely  volatile  sub- 
stance when  exposed  to  the  air,  in  its  combination  with  nitro-cellulose 
it  loses  this  property  altogether.  An  enumeration  of  the  properties  of 
the  material  which  will  be  given  anon  will  be  further  proof  of  the 
chemical  combination.  When  the  material  is  properly  converted  com- 
paratively no  shrinkage  takes  place.  There  is  no  escape  of  the  camphor 
unless  an  excess  has  been  employed,  and  in  that  case  the  excess  of  cam- 
phor will  escape  from  the  surface  of  the  celluloid  ;  but  whatever  uncom- 
bined camphor  remains  in  the  interior  is  so  closely  imprisoned  by  the 
solid  surfaces  that  it  cannot  escape.  By  varying  the  proportions  of 
the  excess  of  camphor  diiferent  degrees  of  solidity  and  flexibility  are 
obtained." 

The  properties  of  celluloid  (noted  in  the  same  article)  are  as  follows : 

"Without  the  admixture  of  coloring  material  it  has  a  pale  amber 
color.  If  it  is  desired  to  make  the  material  white  like  ivory,  oxide  of 
zinc  is  added,  and  for  other  colors  various  mineral  pigments  are  incor- 
porated with  it,  or  dyes  soluble  in  alcohol  or  any  of  the  aniline  dyes 
may  be  caused  to  permeate  the  material  to  give  it  any  desired  color.  It 
is  hard  and  elastic,  having  a  hardness  ranging  from  that  of  horn  to 
that  of  ivory.  It  is  as  tough  as  whalebone.  In  elasticity  it  greatly 
exceeds  ivory 

"  Celluloid  is  also  a  very  fair  non-conductor  of  heat  and  electricity — 
not  equalling  hard  rubber,  but  approximating  the  latter  very  closely  in 


556  CELLULOID  AND  ZYLONITE. 

this  particular Although  a  good  non-conductor,  it  is  not  per- 
ceptibly electric 

"  But  perhaps  the  most  remarkable  property  of  this  material  is  the 
fact  that  it  becomes  plastic  at  a  temperature  of  from  250°  to  300°,  and 
this  property  enables  it  to  be  moulded  with  facility  into  a  great  variety 
of  forms.     Pure  celluloid  has  a  specific  gravity  of  about  1.4. 

"  A  profitable  and  successful  industry  based  upon  these  properties 
of  celluloid  is  the  manufacture  of  dental  plates.  The  material  may  be 
made  precisely  the  color  of  the  natural  palate  and  gums.  It  is  much 
stronger  than  rubber,  and  has  a  perfectly  clean  surface.  It  may  be 
manipulated  more  easily  than  rubber.  It  possesses  many  of  the  valuable 
qualities  of  rubber  for  dental  purposes  without  its  defects.  It  requires 
only  about  one-sixtieth  as  much  vermilion  to  give  the  proper  color  to 
celluloid  as  is  required  to  impart  the  usual  color  to  rubber.  The  diffi- 
culties encountered  in  the  application  of  celluloid  to  dental  plates  have 
been  very  great,  but  the  inventors  continued  experimenting  until  dur- 
ing the  last  few  years  they  claim  to  have  produced  an  article  possessing 
all  the  requirements  desired." 

The  first  process  for  moulding  celluloid  into  dental  plates  was  that 
known  as  the  oil-bath.  The  oil  was  placed  in  a  small  cast-iron  box  or 
tank  containing  the  flask,  and  the  whole  was  heated  to  the  boiling-point, 
the  flask  being  gradually  closed  by  means  of  a  clamp. 

Next  was  the  glycerin  process.  This  certainly  was  an  improve- 
ment, for  if  a  good  quality  of  the  material  was  employed  and  perfect 
cleanliness  preserved,  there  was  no  unpleasant  smell  and  the  glycerin 
was  not  liable  to  become  rancid,  and,  being  readily  soluble  in  water, 
the  flask  could  be  kept  free  from  dirt.  This  process  is  still  used  by 
many  dentists,  the  machines,  etc.,  employed  in  it  having  been  much 
improved. 

The  two  remaining  methods  of  moulding  this  material  are  by  steam 
and  by  dry  heat. 

Dr.  I.  H.  Alexander  was  doubtless  the  first  to  employ  steam  in  the 
manipulation  of  celluloid.^ 

It  is  useless  to  describe  the  steam-heat,  oil,  or  glycerin  process  for 
dental  purposes,  as  they  are  primitive  and  obsolete. 

The  dry-heat  process  now  in  general  use  is  the  one  which  gives 
most  satisfactory  results,  the  proof  of  the  correctness  of  which  opinion 
will  be  clearly  shown  later. 

The  credit  of  having  originated  this  method  belongs  to  Dr.  R.  Find- 
ley  Hunt  of  Washington,  D.  C,  though  other  gentlemen  have  made 
claims  to  the  discovery.  Whoever  may  have  first  conceived  the  idea  of 
this  process,  however,  it  is  certain  that  Dr.  Hunt  practically  applied 
it  first,  and  his  were  the  first  machines  known  to  the  public. 

There  are  several  dry-heat  machines  at  present  in  use  :  the  most  de- 
sirable one,  however,  is  known  as  the  "  Best."  The  advantage  of  this 
machine  over  all  others  lies  in  the  fact  that  in  carrying  the  heat  as  high 
as  is  necessary  to  thoroughly  soften  the  celluloid  the  danger  of  combus- 
tion of  the  highly  inflammable  substance  is  avoided.  If  an  apparatus  is 
used  that  so  confines  the  flask  that  it  cannot  readily  be  removed  from 
the  overheated  oven  at  will,  an  explosion,  resulting  in  the  total  destruc- 
^  Dental  Cosmos,  May,  1875,  p.  280. 


THE  "BEST"   MACHINE. 


557 


tion  of  the  carefully  prepared  work  may  occur.  The  construction  of  the 
"Best"  apparatus  permits  of  the  instant  removal  of  the  flask  if  the  heat 
is  too  great  for  safety,  while  the  plate  remains  under  pressure,  owmg  to 
thP  screw-clamp  being  attached  to  the  top.  Another  advantage  is  that  the 
work  can  beTadily  e^xamined  from  all  sides.    The  illustration  (Fig.  684) 


is  so  comprehensive  as  to  scarcely  need  explanation.  The  bottom  plate 
is  connected  with  the  top  by  three  wrought-iron  screw-bolts,  the  nuts 
being  on  the  upper  side  and  easv  of  access.  When  these  nuts  are  turned 
for  the  purpose  of  closing  the  clamp,  the  bottom  portion  is  drawn  away 
from  the  flame  and  from  the  overheated  bottom  of  the  oven,  thus  grad- 
ually decreasing  the  heat  without  disturbing  the  flame.  ,  .  ,    , 

Equally  desirable  ovens  for  baking  celluloid  are  those  which  have  a 
dry  oven  surrounded  by  steam.  Machines  so  constructed  have  the  Al- 
lowing advantages :   First,  danger  of  burning  the  plate  is  avoided,  in 


558 


CELLULOID  AND  ZYLONITE. 


which  respect  they  are  safer  than  the  dry-air  chambers;  secondly,  the 
temperature  may  be  carried  to  a  much  higher  degree,  a  more  thorough 
softening  of  the  material  be  attained,  and  the  two  parts  of  the  flask  be 
brought  together  with  greater  facility. 

Of  these,  the  two  most  satisfactory  are  the  ''  NeM^  Mode  "  heater  of 
Dr.  J.  S.  Campbell  and  one  devised  by  the  writer.  The  former  of 
these  is  well  known ;  the  latter,  shown  in  Fig.  685,  is  described  as  fol- 
lows :  No.  1  shows  a  front  elevation  of  the  machine  ready  for  use,  with 
top  fastened  down,  and  tools  used  in  its  manipulation.  No.  2  illustrates  a 
transverse  vertical  section  with  one  flask  in  position,  showing  the  manner 
of  working  zylonite,  celluloid,  or  other  material.  ^  is  a  light  casing 
surrounding  and  supporting  the  apparatus.  B  is  the  boiler,  composed 
of  two  separable  cups  of  best  quality  gun-metal,  6  6,  united  concentrically 
by  screws,  h' ,  to  form  a  water  and  steam  space.  The  object  of  this  form 
of  construction  is  obvious.  It  avoids  complicated  coring  in  casting; 
both  sections  may  be  examined  before  being  fitted  together,  thereby  ren- 
dering it  certain  that  sound  castings  are  employed,  Avhich  aid  greatly  in 
ensuring  safety  in  the  use  of  the  apparatus.     The  boiler.  A,  is  made 


Fig.  685. 


No.  2. 


partly  concave;  thus,  contracting  the  water  space  in  the  interior, 
so  that  steam  is  not  only  produced  more  rapidly,  but  is  kept  in  a 
state  of  agitation,  thus  producing  a  more  desirable  quality  of  heat. 
D  illustrates  the  oven,  composed  of  the  inner  cup,  b,  having  a  cover  C, 
an  inlet  for  steam  d  through  the  cup  6  from  the  boiler,  and  an  exit  for 
steam  through  the  cover  at  d",  both  openings  being  controlled  by  valves 
d'  and  d'".  E  E,  the  bolts,  represent  the  next  great^  feature  of  safety 
and  convenience  in  this  machine :  their  heads  are  spherical  at  c,  the  point 
of  contact  with  the  cover  c,  which  has  a  corresponding  socket  to  receive 
it,  thus  making  a  steam-tight  joint.     The  top  of  the  head  c"  is  made  to 


USE  OF  THE  EVANS  HEATER.  559 

iit  the  T-wrench,  which  also  fits  the  different  valves.  Pressure  from 
this  is  usually  all  that  is  required,  but  to  make  it  applicable  to  the  use  of 
all  an  additional  hexagonal  portion  c'  has  been  made,  whereby  any 
amount  of  desirable  pressure  can  be  exerted.  The  lower  portion  of  the 
bolt  is  threaded  for  one-half  its  length  and  screwed  into  or  through 
the  plate  F,  which  is  drawn  toward  the  top  by  turning  the  bolts  to  the 
right,  thus  closing  the  flask  or  flasks  with  great  facility  and  without  the 
slightest  strain  upon  the  boiler,  as  must  of  necessity  be  the  case  with  any 
apparatus  having  down-plungers  which  exert  a  strong  leverage  to  force 
top  and  bottom  asunder.  /  is  the  thermometer  attached  to  the  boiler  by 
a  ground  joint  and  bevel-faced  coupling,  which  makes  a  steam-tight  joint 
and  allows  the  face  of  the  scale  to  come  to  the  front.  The  bulb  of  the 
mercury  tube  is  encased  within  a  small  copper  tube  passing  down  into 
the  steam  through  the  plug  which  enters  into  the  boiler.  This  brings 
the  mercury  almost  into  direct  contact  with  the  steam,  making  it  quite 
sensitive  to  changes  of  temperature,  at  the  same  time  protecting  the  tube 
from  fracture.  The  cup-like  mouth  of  the  plug  also  serves  to  fill  the 
boiler  with  water. 

On  either  side  of  the  thermometer  are  the  valves,  one  connecting  the 
boiler  with  the  oven,  as  before  described ;  the  other,  a  simple  conical 
safety-valve,  resting  against  a  small  hole  through  the  plug  into  the  boiler, 
and  held  in  place  by  a  heliacal  spring,  exteriorly  adjusted  by  a  perforated 
set-screw  so  arranged  that  the  steam  in  the  boiler  can  never  go  higher 
than  the  point  at  which  you  set  the  safety-valve  without  blowing  off" 
through  the  perforated  screw-plug,  thus  preventing  any  possibility  of 
explosion  through  neglect  or  carelessness. 

/  designates  a  handle  whereby  the  top  is  readily  removed  to  examine 
the  work,  etc. 

The  machine  is  simple,  carefully  adjusted,  and  having  but  one  pack- 
ing anywhere  about  it,  is  therefore  not  liable  to  get  out  of  order. 

It  has  plenty  of  room  for  two  large  flasks  at  a  time,  yet  the  outside 
measurement,  case  and  all,  is  not  over  10  inches  high  by  7^  in  diameter, 
and  will  readily  stand  from  250  to  300  pounds'  pressure. 

Use  of  the  Evans  Heater. 

Having  raised  the  heat  to  320°  in  the  boiler  while  preparing  the 
work  for  moulding,  put  something  between  the  jaws  of  the  flask  in  order 
to  keep  them  apart  to  facilitate  drying,  and  place  it  on  top  of  the  plate 
in  the  oven,  first  noticing  that  the  valve  connecting  boiler  and  oven  is 
closed ;  then  partly  open  the  valve  in  the  top,  and  leave  the  piece  from 
half  an  hour  to  one  hour  to  dry  out ;  then  raise  the  top  and  touch  the 
flask  with  a  wet  finger ;  if  hot  enough  to  produce  a  hissing  sound,  the 
flask  is  ready  for  the  blank.  Having  adjusted  the  blank  between  the 
two  halves  of  the  flask  after  trimming  to  the  desired  size,  replace  in  the 
oven,  leaving  the  lid  loose,  but  nearly  closing  the  top  valve ;  in  from 
ten  to  fifteen  minutes  gently  turn  the  bolts  with  the  T- wrench.  If 
there  is  no  resistance,  close  immediately ;  should  there  be  much  re- 
sistance, wait  a  few  minutes  longer,  then  turn  first  with  the  T-wrench ; 
should  the  blank  be  a  little  heavy,  use  the  long  wrench,  taking  each  bolt 
alternately  after  one  turn,  raising  the  top  now  and  then  to  see  if  the  flask 


560 


CELLULOID  AND  ZYLONITE. 


Fig.  686. 


\\\l 


is  closed.     When  done  raise  the  lid,  which,  in  reality,  is  a  clamp  or  press 
separate  and  distinct  from  the  boiler,  and  either  set  by  to  cool  slowly,  or 

plunge  into  water  and  cool  immediately. 
Cooling  slowly  is  the  proper  way  to  allow 
the  newly  moulded  material  to  season. 
It  will  be  observed  that  in  the  manipulation 
of  the  screw-press  top  of  the  machine  the 
action  is  similar  to  that  of  the  ''  Best "  aj)- 
paratus,  and  there  is  probably  no  way  to 
materially  improve  on  that  device  for  safety 
and  simplicity. 

A  simple  form  of  lock  flask  is  an  ad- 
vantage when  more  than  one  piece  is  to 
be  moulded,  as  it  may  be  locked,  taken  out 
of  the  press,  and  set  by  to  cool,  while  work 
is  continued  with  other  pieces.  The  entire 
time  consumed  in  drying  out  and  closing 
the  flask  should  not  exceed  an  hour  to  an 
hour  and  a  half.  As  no  steam  is  lost 
fj-  rjr^  from  the  boiler,  a  dozen  pieces  can  be 
moulded,  if  desired,  in  a  day.  Any  sized 
flasks,  of  any  description,  can  be  used, 
whether  lock  or  otherwise. 

Before  proceeding  to  describe  the  method 
of  working  celluloicl  it  may  be  well  to  give 
some  further  reasons  why  the  peculiar  dry 
heat  produced  by  steam  is  superior  to  either 
a  steam-bath  or  direct  dry  heat. 

Celluloid  is  peculiar.  To  be  properly 
managed  it  must  be  understood.  It  must 
be  studied,  manipulated  carefully,  and  con- 
trolled, for  it  has  a  character  of  its  own.  Re- 
cent experiments  of  Professor  Tarr  of  the 
Georgetown  University  lead  to  the  belief 
that  it  is  merely  a  mechanical  admixture, 
the  microscope  showing  very  clearly  the 
two  most  important  constituents,  camphor 
and  gun-cotton,  in  their  natural  state.  In 
these  experiments  thin  specimens  of  pure 
celluloid  before  treatment  and  after  be- 
ing put  into  the  heater  were  examined 
under  a  microscope  having  a  power  of 
three  hundred  diameters,  and  viewed  by 
transmitted  light  revealed  a  structure  irregu- 
lar and  grooved,  with  flinty  appearance  and 
protuberances  of  black  specks.  Stray 
threads  of  nitro-cellulose  were  noticed  in 
some  cases  corresponding  with  the  grooves. 
In  one  instance,  the  specimen  having  been 
disturbed,  a  fibre  was  displaced  and  the 
underlying  groove  distinctly  seen.     The  same  specimen  seen  by  reflected 


i^ 


ii!X-L 


Set  of  carvers. 


WORKING   CELLULOID  AND  ZYLONITE.  561 

light  displayed  a  clear,  crystal-like  surface,  similar  in  appearance  to  a  heap 
of  small  pieces  of  camphor,  and  the  black  specks  noticed  before  were 
very  like  protruding  shreds  of  cotton.  This  would  seem  to  indicate  that 
the  pyroxylin  and  camphor  had  not  united  chemically,  but  were  merely 
mechanically  mixed,  and  by  means  of  the  great  pressure  exerted  upon 
them  formed  into  a  solid  mass.  In  order,  however,  to  make  assurance 
doubly  sure,  pieces  of  pure  gun-cotton  were  examined  under  the  same 
glass,  and  no  distinction  could  be  observed  between  them  and  those 
discovered  in  the  celluloid.  A  thin,  transparent  wafer  of  camphor  also 
was  examined,  and  the  appearance  was  exactly  the  same  as  that  of  the 
main  body  of  the  celluloid,  without  the  black  specks. 

Before  going  farther  into  this  portion  of  the  subject  an  approved 
method  of  working  celluloid  and  zylonite  is  to  be  described,  the  discus- 
sions of  the  causes  of  success  and  failures  in  manipulation  will  follow, 
togetlier  with  an  examination  of  the  relative  merits  of  celluloid  and 
zylonite. 

Imprimis,  a  good  impression  is  indispensable.  For  taking  impres- 
sions plaster  is  preferable  in  all  cases,  and  by  all  means  should  be  used 
where  partial  impressions  are  to  be  taken.  No  time  or  trouble  should 
be  spared  in  securing  an  accurate  occlusion  for  the  articulation.  Having 
procured  this  solid  foundation,  next  make  upon  the  model  a  wax  plate 
of  the  same  thickness  which  the  celluloid  plate  is  to  have,  or  a  little 
thinner.  Care  in  this  particular  is  essential.  The  pink  paraffin  and  wax 
for  the  purpose  found  in  the  dental  depots  in  the  form  of  thin  sheets  and 
in  sticks  is  admirably  adapted  for  this  purpose.  The  reasons  for  using 
this  wax  rather  than  others  are  obvious :  it  is  cleanly,  does  not  soil  or 

Fig.  687. 


stick  to  the  hands  or  teeth,  is  dry  and  carves  well,  and,  as  it  is  nearly 
the  color  of  the  gums,  it  serves  as  a  convenient  guide  for  modeling.  In  an 
upper  plate  only  one  thickness  of  the  wax  over  the  palatal  portion  is 
necessary.  Warm  the  wax  and  press  it  gently  over  the  model,  exhibit- 
ing in  relief  any  rugse,  etc.  which  may  exist.  Select  the  plain  teeth 
made  for  celluloid,  as  they  are  probably  the  most  natural  in  shape  and 
shade  of  any  now  made  for  the  purpose,  and  permit  a  greater  display  of 

36 


562 


CELLULOID  AND  ZYLONITE. 


skill  and  taste  than  any  others.     The  grinding  and  arrangement  of  the 
teeth  are  to  be  regulated  by  the  features  of  the  case  in  hand. 

This  is  a  distinct  and  extensive  study  in  itself,  and  could  scarcely  be 
treated  thoroughly  under  this  head.  The  next  step,  the  carving,  is  a 
very  simple  performance,  provided  sufficient  study  of  the  forms  and 
arrangements  of  natural  teeth  has  been  made,  together  with  observations 
of  irregularities,  effects  of  diseases,  etc.  With  models  representing  these 
features  before  the  operator,  and  a  remembrance  of  the  face  of  which  it  is 
intended  to  restore  the  features,  the  operation  is  not  a  difficult  one.  For  use 
in  carving  three  little  double-end  tools,  represented  in  Fig.  686,  are  re- 

FiG.  688. 


quired,  the  uses  of  each  of  the  points  of  which  will  be  explained.  Fig. 
687  presents  a  full  set  of  teeth  in  process  of  carving,  the  upper  half, 
shown  by  B,  having  on  it  the  rough  wax  as  dropped  there  while 
grinding  and  adjusting  the  teeth,  the  lower  denture,  at  C,  shoAving 
w^here  the  wax  has  been  cut  away  from  the  teeth  in  scallops  by  the 
straight-bladed  knife  of  carver  No.  2,  and  roughly  shaped  up  with  the 
spoon  end  of  the  same  instrument.  Next  is  used  the  smaller  spoon  end 
of  No.  1  to  form  the  fossae  or  depressions  lying  between  the  roots,  and  the 
curved  knife-blade  of  the  same  to  go  around  the  teeth  on  the  palatal  side. 
Having  carved  the  wax  in  this  way,  forming  festoons  or  exposing 
roots  as  the  case  may  require,  take  a  spirit-lamp  with  a  small  flame  and 
an  air-bulb  (which  is  better  than  a  blowpipe),  and  by  gently  puffing 
upon  the  wax  smooth  away  the  rough,  irregular  projections  while  retain- 
ing the  larger  undulations  of  the  form  desired.  This  case  is  now  ready  for 
the  tin-foil  and  stippling.     Take  a  strip  of  No.  60  tin-foil  a  little  wider 


INVESTING   THE  PIECE  IN  THE  FLASK. 


563 


than  the  outside  surface  of  the  gum,  and  by  commencing  at  one  side 
with  the  broad  end  of  the  ivory-pointed  carver  No.  3  burnish  the  tin 
down  smoothly  and  uniformly  over  the  entire  surface,  occasionally  using 
the  pointed  end  to  work  between  the  teeth,  and  the  straight  blade  of 
carver  No.  1  to  cut  the  tin  from  around  the  teeth.  The  inside  of  the 
model  is  treated  in  the  same  way,  except  that  a  narrow  V-shaped  piece 
is  cut  from  the  tin  before  placing  it  on  the  palatal  surface,  to  avoid 
folding,  and  that  the  entire  outer  edge  of  the  plate  is  trimmed  around. 
The  stippling  is  done  with  an  ordinary  blunt-pointed  excavator  or  with 
an  engine-plugger  which  will  give  a  reacting  blow.  If  done  delicately 
and  closely,  the  effect  of  the  stippling  is  very  pleasing. 

The  investing  of  the  piece  in  the  flask  seems  simple  enough,  and  yet 

Fig.  689. 


a  few  suggestions  may  be  of  benefit.  Always  mount  the  model  high  in 
the  shallow  half  of  the  flask  (see  Fig.  688),  for  reasons  hereafter  ex- 
plained. Pour  the  plaster — neither  too  thick  nor  too  thin,  but  of  about 
the  consistence  of  syrup — until  it  reaches  the  lower  edge  of  the  plate,  no 
higher.  When  sufficiently  hard,  trim  and  use  liquid  soap  as  a  separa- 
ting material,  as  varnish  is  more  or  less  dirty  and  will  soil  the  work. 
Place  on  the  deep  ring  and  pour  in  the  plaster,  taking  care  to  have  no 
air-bubbles.  Then  with  a  little  stick  (an  ordinary  wooden  toothpick) 
stir  gently  to  and  fro  around  the  outside  of  the  teeth  to  work  the 
plaster  into  every  little  crevice  between  them.  Put  on  the  top,  wash 
the  outside  of  the  flask  clean  of  the  surplus  plaster  which  has  oozed  out, 


564  CELLULOID  AND  ZYLONITE. 

and  place  it  under  gentle  pressure  until  set — say,  for  half  an  hour  or 
more. 

If  there  are  any  undercuts,  put  the  flask  into  hot  water  a  few  moments 
before  separating  it,  to  soften  the  wax  and  prevent  breakage.  Hav- 
ing separated  the  flask,  pour,  from  a  pitcher  or  other  convenient  vessel 
with  a  spout,  boiling  water  on  the  wax  until  all  is  washed  out,  taking 
care  not  to  disturb  the  tin-foil. 

There  are  several  ways  of  cutting  vents  for  surplus  material,  but  the 
one  illustrated  in  Fig.  689  is  preferable — the  upper  half  of  the  flask  shown 
in  Fig.  688.  The  wax  has  been  washed  out,  exposing  to  view  the  roots 
of  the  teeth,  platinum  pins,  etc.  ready  to  receive  the  base-plate,  the  stip- 
pled tin-foil  clinging  to  the  sides  of  the  plaster.  B  indicates  a  portion  of 
plaster  cut  away,  illustrating  the  manner  of  forming  vents  ;  in  this  cut  it 
is  only  carried  half  around,  so  as  to  show  before  and  after  preparing. 
Commence  by  cutting  a  deep  groove  all  around  the  piece  close  to  the 
flask  and  gradually  tapering  up  to  the  tin-foil  or  the  margin  of  the 
plate,  marked  C  By  this  arrangement  the  material  has  free  exit  all 
around,  yet  may  not  come  out  too  rapidly.  The  plaster  margins  are  not 
likely  to  be  broken  away  under  pressure,  as  the  vent  runs  out  ahuost  at 
a  right  angle,  thus  leaving  solid  walls.  Another  advantage  in  this  form 
of  vent  is  that  after  the  two  halves  of  the  flask  have  been  pressed  home 
the  surplus  material  parts  readily  from  the  piece,  leaving  very  little  to 
dress  up. 

The  process  of  baking  follows :  it  is  unnecessary  to  describe  the 
manner  of  conducting  this  by  the  steam  method.  To  bake  by  dry 
heat  requires  perhaps  a  little  longer  than  by  other  means,  on  account 
of  the  necessity  of  expelling  the  surplus  moisture  from  the  plaster  in  the 
flask.  Place  the  flask  in  the  dry  oven,  having  first  slipped  two  small 
spools  over  the  guide-pins  to  keep  the  halves  apart,  and  close  up  all  the 
openings  to  the  oven  except  the  small  valve  communicating  with  the 
outer  air  from  the  dry  chamber,  as  this  must  be  left  to  carry  off  the 
steam  generated  from  the  moisture  in  the  plaster.  Then  raise  the  steam 
in  the  boiler  to  320°  or  330°,  and  keep  it  there.  This  will  give  a 
temperature  of  about  300°  in  the  dry  chamber.  Let  the  flask  dry 
out  for  not  more  than  an  hour,  and  then  when  touched  with  a  wet  finger, 
as  the  laundress  does  her  smoothing-iron,  the  same  "  sizzle "  will  be 
produced.  The  case  is  now  ready  for  the  celluloid  blank,  which 
must  first  be  trimmed  to  the  proper  size,  trying  always  to  have  a  slight 
excess,  but  being  careful  not  to  have  too  much.  It  is  a  mistake  to  use  a 
very  great  amount  of  pressure  at  any  stage  of  the  process.  Replacing 
the  flask  containing  the  blank  in  the  oven,  leave  it  there  from  ten 
to  fifteen  minutes  to  soften  ;  then  try  its  resistance  by  carefully  turn- 
ing the  bolts  for  that  purpose.  Be  sure  that  the  bolts  work  easily 
and  are  true.  The  sensation  of  touch  upon  the  wrench  is  the  surest 
index  of  the  amount  of  pressure  being  employed ;  and  this,  in  the 
beginning,  should  not  be  more  than  can  be  exerted  with  the  thumb  and 
finger.  The  operator  may  raise  the  lid  and  see  if  the  blank  is  soft 
by  touching  it  with  an  instrument.  As  soon  as  the  material  has 
become  soft  enough,  close  the  flask  immediately,  occasionally  resting  a 
moment  between  the  turns  to  give  the  zylonite  time  to  spread.  The 
operation  of  closing  the  flask  usually  occupies  from   five  to  twenty 


REPAIRING   THE  MATERIAL.  565 

minutes.  When  it  is  closed  tightly — and  pressure  should  not  cease 
until  it  is  tight,  in  order  to  retain  a  perfect  articulation  of  the  teeth — it 
is  better  to  leave  the  case  a  few  minutes  under  heat  to  season,  when  it 
may  be  taken  out  if  in  a  lock-flask  in  the  "  New  Mode  "  vulcanizer ;  or 
if  in  the  Evans  heater  raise  the  top,  which  in  reality  forms  a  clamp  or 
press,  and  set  it  out  of  the  window  or  in  some  other  cool  place  to  temper 
down.  If  a  lock-flask  has  been  used,  so  much  additional  time  can  be 
gained,  but  the  flask  should  never  be  cooled  suddenly  in  practical  work, 
and  never  be  freed  from  pressure  from  the  moment  it  is  closed  until 
perfectly  cold  :  one  causes  warpage ;  the  other,  shrinkage  from  the  teeth. 

Care  should  be  exercised  in  removing  the  piece  from  the  flask,  on 
account  of  the  hardness  the  plaster  acquires  when  subjected  to  the  dry-heat 
process.  Having  taken  ofl"  the  top  and  Ijottom,  lay  the  flask  in  warm 
water  for  a  few  minutes.  Then  press  a  knife-blade  between  the  two 
rings,  and  a  gentle  movement  will  cause  one  or  the  other  to  leave  the 
plaster,  when  the  remaining  one  is  easily  detached  by  a  few  blows  of  a 
hammer  on  its  wide  edge  :  knowing  the  position  of  the  teeth,  it  is  now 
an  easy  matter  to  get  the  piece  out  whole.  Wash  off  the  plaster  which 
may  adhere  to  it,  trim  away  the  surplus,  remove  the  tin-foil,  and,  finally, 
having  scraped  and  smoothed  the  edges  with  felt  and  pumice-stone,  pro- 
duce a  high  polish  of  the  entire  surface  with  brush-wheels,  pumice,  and 
chalk,  taking  care  not  to  use  too  much   friction. 

Repairing  this  material  is  not  so  diflicult  as  it  appears,  the  process 
being  very  similar  to  that  employed  in  mending  rubber.  If  the  plate 
is  comparatively  new,  having  been  lately  made,  there  is  no  special 
need  of  a  great  deal  of  "  dovetailing,"  as  the  material  with  its  solvent 
will  readily  unite.  If,  however,  the  piece  to  be  mended  is  old,  scrape 
away  the  edges  of  the  fracture,  dovetail,  and  drill  two  or  three  holes 
through  the  plate,  reaming  them  on  the  inner  surface  in  order  to  clinch 
the  material  when  it  goes  through.  Then  wax  these  holes  smooth  on 
the  inner  surface  with  paraffin  and  wax ;  restore  the  outer  surface  with 
the  same  material  to  the  original  shape,  and  with  the  new  teeth,  if  any, 
in  place,  invest  in  a  flask,  covering  all  except  the  parts  to  be  repaired. 
After  separating  the  flask  wash  out  the  wax  Avith  boiling  water,  and 
moisten  the  portions  previously  covered  with  it  with  spirits  of  camphor 
or  the  liquid  zylonite  or  celluloid,  made  of  one  part  zylonite  scraps  in 
three  parts  spirit  of  camphor.  Then,  preparing  a  piece  of  new  blank  a 
trifle  larger  than  is  actually  needed,  soak  it  in  the  camphor  mixture 
until  it  becomes  sticky,  place  it  in  position  between  the  two  halves  of 
a  flask,  and  heat  the  whole  in  the  oven,  as  directed,  twenty  minutes  or 
half  an  hour,  and  screw  home.  If  steam  be  used,  but  a  few  minutes 
need  be  allowed  to  soften  the  celluloid,  and  then  the  flask  may  be  imme- 
diately closed.  By  pursuing  this  course,  taking  care  to  have  everything 
clean,  absolute  mechanical  union  will  be  obtained,  unless  the  piece  is 
quite  old  or  has  been  baked  by  one  of  the  liquid  processes  or  by 
steam.  It  sometimes  happens  tliat  through  a  desire  to  be  too  exact 
not  quite  enough  material  is  used,  a  pin  or  two  may  be  left  partly  ex- 
posed, a  slight  corner  left  out,  or  some  other  little  defect  of  a  like  sort 
caused — not  enough  to  interfere  with  the  fit  of  the  plate  or  to  loosen  a 
tooth,  but  enough  to  annoy  the  critical  sense  of  one  who  appreciates 
symmetry  and  a  nice  finish.      To  correct  these  slight  blemishes   use 


566  CELLULOID  AND  ZYLONITE. 

zylonite  filings  moistened  in  spirits  of  camphor,  and  press  gently  into 
the  inequalities  with  a  heated  burnisher — not  too  hot,  by  the  way.  Allow 
such  pieces  to  stand  a  while  before  the  final  polishing  and  finishing. 
Another  convenient  way  to  put  in  a  tooth  without  loss  of  time  is  to  cut 
out  the  broken  portions,  dovetail,  grind  in  the  tooth,  and  unite  to  the 
plate  with  amalgam. 

The  following  are  a  few  of  the  more  important  of  the  queries  made 
concerning  this  suWect : 

First,  it  has  beeh  inquired  what  kind  of  plaster  should  be  used  for 
models,  and  how  can  they  be  gotten  quite  hard.  Use  the  ordinary 
best  Newburg  plaster  employed  by  the  plasterers  in  house-decorations, 
such  as  cornices,  etc.  It  is  strong,  sufficiently  fine  and  smooth,  and  if 
properly  manipulated  will  make  very  hard  models,  the  hardness  of  which 
is  increased,  if  when  they  are  dry  and  absorptive,  they  are  dipped  into  a 
boiling  solution  of  borax  or  into  a  solution  of  1  part  of  silex  in  5  of 
water. 

Again,  it  is  asked  why  and  how  should  models  be  obtained  quite 
smooth  and  free  from  air-bubbles,  nicks,  bruises,  etc.  The  reason  is,  that 
the  model  represents  the  mouth  exactly,  or  should  do  so,  and  that  any 
blemish  upon  its  surface  must  necessarily  be  transferred  to  the  plate,  and 
will  afterward  irritate  the  mucous  membrane,  if  not  materially  affect  the 
fit  of  the  piece.  This  is  a  matter  about  which  most  dentists  are  usually 
very  careless. 

If  vacuum- chambers  are  used,  they  should  be  carved  from  the  im- 
pressions before  pouring.  It  might  perhaps  be  well,  too,  to  answer  here 
the  question  whether  tin  models  should  always  be  used.  Much  the 
better  results  are  obtained  by  their  employment,  except  where  it  is  ex- 
tremely inconvenient  to  do  so ;  and  for  several  reasons  :  First,  a  tin 
model  under  pressure  with  teeth  and  undercuts  is  not  likely  to  break ; 
second,  the  microscope  reveals  the  fact  that  the  surface  of  the  celluloid 
is  made  more  dense  in  structure  where  it  comes  in  contact  with  tin  or 
tin-foil  than  where  simply  pressed  on  plaster ;  third,  tin-foil  cannot  be 
placed  on  the  model  without  materially  affecting  the  accuracy  of  the  fit ; 
and  fourth,  a  model  of  the  case  can  always  be  retained.  A  tin  model — 
or  a  tin  shell  of  a  model,  which  is  even  better,  because  there  is  no  per- 
ceptible shrinkage,  is  lighter,  and  takes  less  material — can  be  made  in 
less  than  ten  minutes  if  all  the  requisites  are  convenient.  A  sand  matrix 
is  made :  and  into  it  molten  tin  is  poured :  while  the  body  of  the  tin  mould 
is  still  fluid  the  matrix  is  inverted,  permitting  the  fluid  metal  to  run  out, 
leaving  a  tin  shell  model. 

One  of  the  charges  against  celluloid  is  that  it  is  not  stable  enough, 
but  this  charge  does  not  seem  to  be  founded  on  fact ;  for  by  comparing 
its  durability  with  that  of  other  substances  the  following  conclusions 
have  been  reached  :  The  mean  durability  of  vulcanite  plates  is  over- 
estimated. A  fair  average  of  their  life  is  very  probably  not  more  than 
eight  to  ten  years.  Of  course,  many  last  longer,  but  these  are  the  ex- 
ceptions, and  many  do  not  last  a  single  year.  Continuous  gum,  except 
as  manipulated  by  experts,  is  continually  breaking,  and  is  decidedly 
expensive  and  annoying.  Celluloid  has  been  in  existence,  for  dental 
plates  at  least,  only  about  eighteen  or  twenty  years,  and  yet  many  plates 
of  this  material  have  been  worn  with  satisfaction  for  eight  or  ten  yeai^s. 


THE   WARPING    OF  PLATES.  567 

The  warping  of  plates  may  be  caused  in  several  ways.  If  the  mate- 
rial is  pressed  home  under  high  pressure  and  at  a  low  temperature,  the 
plate,  having  yielded  to  the  pressure,  necessarily  tends  to  revert  to  its 
original  shape  by  reason  of  its  great  elasticity,  no  radical  displacement 
of  the  particles  having  taken  place.  And  if  the  flask  is  removed  from 
under  pressure  before  it  is  thoroughly  cold,  there  is  again  a  tendency  to 
warp.  Heating  the  plate  with  friction  in  polishing  will  also  cause  this 
evil,  as  it  does  with  rubber.  If  these  causes  can  be  avoided,  there  is  no 
reason  why  a  plate  should  warp. 

These  accidents  are  the  result  of  carelessness,  but  the  waxing  of 
plates  can  only  be  obviated  by  the  use  of  that  class  of  machines 
which  permit  of  carrying  the  temperature  high  enough  to  make  the 
material  thoroughly  plastic,  so  that  it  will  yield  readily  to  light  pres- 
sure. In  this  state  the  cohesive  force  of  the  molecules  of  the  body 
being  reduced  to  a  very  small  quantity,  they  will  evince  no  tendency 
to  return  to  their  former  position  after  a  displacement,  and  a  change 
may  be  produced  in  their  relative  positions  which  will  become  per- 
manent when  the  cooling  of  the  plate  allows  the  force  mentioned  to 
again  exert  its  influence.  But  it  is  claimed  by  the  advocates  of 
steam  machines  that  this  higli  temperature  of  280°  and  upward  is 
very  injurious  to  the  plates,  and  also  that  "  too  little  pressure  after 
the  heat  is  up  "  will  cause  the  same  result — the  puffing  up,  that  is,  of 
the  material  and  its  filling  with  air-cells,  etc.  These  assertions  are 
probably  correct  when  applied  to  the  process  of  moulding  in  steam,  but 
Avhen  applied  to  tlie  process  in  which  celluloid  or  zylonite  is  softened  in 
a  dry  chamber  which  is  surrounded  by  steam  they  are  not  true. 

It  is  believed  that  celluloid  is  cellular  in  structure,  and,  as  a 
consequence,  when  it  is  heated  and  expands  its  cells  absorb  the  sur- 
rounding medium  as  a  sponge  absorbs  water.  If  this  medium  be 
oil  or  glycerin,  the  cells  are  tilled  with  it,  and  the  subsequent  pres- 
sure serves  to  close  their  orifices  without  expelling  the  liquid.  On 
cooling,  consequently,  the  moisture  throughout  the  interior  of  the  sub- 
stance softens  the  walls  of  the  cells  and  they  crumble  away.  If  steam 
be  used,  when  the  plate  cools  the  vapor  is  condensed  and  its  expansive 
force  becomes  almost  nothing,  and  therefore,  in  addition  to  the  softening 
effects  of  the  moisture,  the  walls  of  the  cells  are  required  to  sustain  the 
pressure  of  the  atmosphere  and  of  cohesion  without  any  internal  sup- 
port. The  celluloid  ought,  it  would  seem,  therefore,  to  crumble  even 
more  rapidly.  When,  on  the  other  hand,  the  plate  is  moulded  in  con- 
tact with  dry  air,  while  the  cells  still  imbibe  the  surrounding  medium, 
it  is  a  medium  without  moisture,  and  of  at  least  considerable  expansive 
force  even  when  cooled.  The  plate  therefore  remains  smooth  and  com- 
pact. 

The  following  figures  were  originally  prepared  from  practical  cases 
for  illustrating  an  article  in  the  Dental  Cosmos,  July,  1880,  but  as  they 
were  made  with  single  teeth  mounted  upon  celluloid  base,  they  are 
reproduced  to  illustrate  how  perfectly  this  material  with  the  use  of 
single  teeth  can  be  moulded  to  restore  expression  in  the  human  counte- 
nance. The  illustrations  are  figured  from  practical  models  of  charac- 
teristic mouths.  Fig.  690  represents  two  sets  of  six  front  teeth  from 
the  same  mould — one  as  it  leaves  the  mould  and  is  found  in  stock  ;  the 


568 


CELLULOID  AND  ZYLONITE. 


other  showing  alterations  by  grinding  to  suit  a  different  case.  Figs. 
691  and  694  represent  two  sets  of  mounted  teeth,  both  from  the  same 
mould  (shown  in  Fig.  690). 


Fig.  690. 


Fig.  691. 


Fig.  692. 


A 


Fig.  691  represents  a  younger  mouth  than  is  often  found  requiring 
a  full  set  of  artificial  teeth ;  but  in  order  to  show  the  different  cha- 
racteristics of  youth  and  age 
which  may  be  produced  from  the 
same  set  of  teeth,  the  model  of 
the  denture  of  a  young  lady  of 
about  eighteen  years  of  age  was 
followed,  reproducing  the  slight 
irregularities  existing  in  her  case. 
The  artificial  teeth  illustrated  in 
Fig.  690  were  so  well  adapted  to 
the  case  that  very  little  modifica- 
tion by  grinding  was  necessary, 
even  the  cusps  of  the  bicuspids 
and  molars  scarcely  requiring  to 
be  touched  by  the  corundum 
wheel  (see  side  view,  Fig.  692), 
thus  preserving  the  original  form  of  the  artificial  teeth  almost  intact. 
The  cutting  edges  have  the  rounded  appearance  so  generally  found 
in  harmony  with  the  general  physique  at  this  age,  the  serrations  found 
at  an  earlier  period  having  all  disappeared.  Fig.  693  shows  a  palatal 
view  of  the  same  case,  and  certainly  indicates  that  a  vast  improve- 
ment of  the  grinding  surfaces  has  been  made  by  the  manufacturer. 
The  cusps  and  intervening  sulci  are  clear  and  well  formed,  requiring 
in  any  case  but  little  labor  on  the  part  of  the  dentist  to  make  a  perfect 
occlusion. 

Fig.  694  shows  the  front  view  of  a  set  of  teeth  for  a  male  fifty  or 
sixty  years  of  age.  It  is  somewhat  of  the  Celtic  order,  though  not 
what  would  be  considered  a  pure  type.  This  case  has  a  "  square 
bite "  upon  the  cutting  edges,  producing  slight  abrasion,  and  with 
just  enough  irregularity  to  produce  a  pleasing  effect.  The  gums  show 
slight  recession  from  the  necks  of  the  superior  teeth,  more  marked 
in  the  inferior  incisors  and  cuspids,  and  accompanied  in  the  latter  with 
a  congestion  of  the  gums,  making  the  festoons  more  prominent  than 


MODIFICATIONS  IN  A  SET  OF  TEETH. 


569 


normal.  The  prominence  over  the  superior  cuspids  will  strike  some  as 
being  too  great,  but,  considering  the  inclination  of  the  roots  and  the 
contraction  of  the  arch  back  of  these  teeth,  it  is  not  too  marked,  as 
is  more  clearly  shown  in  Fig.  695,  a  side  view  of  the  same  case.     In 


Fig.  693. 


the  lower  maxilla  the  first  molar  is  missing,  and  the  second  molar 
has  moved  forward  just  enough  to  adjust  itself  to  a  solid  occlu- 
sion, the  absorption  of  the  alveolar  process  causing  a  greater  recession 
of  the  gums  at  the  necks  of  the  second  bicuspid  and  molar  than  else- 


FiG.  694. 


Fig.  695. 


^ '-     1     '  \iv 


^y  yx^vVvi^^ 


where.  The  abrasion  of  the  cutting  edges  is  best  shown  in  Fig.  696,  a 
palatal  view  of  the  same  case,  more  marked  upon  the  incisors  and  cus- 
pids than  upon  the  bicuspids  and  molars,  owing  to  a  perfect  lock  occlu- 
sion, as  shown  in  Figs.  694  and  695.  The  cutting  edges  of  the  front 
teeth  have  been  stained  to  imitate  the  eifect  of  tobacco  upon  the  de- 
nuded dentine.  The  rug'se  in  the  cut  show  a  direct  transfer  from  the 
model  upon  which  the  ease  was  mounted. 

The  modifications  which  can  readily  be  made  in  the  expression  of 
a  set  of  teeth  by  shading,  by  grinding,  and  in  mounting  will  surprise 
any  one  who  has  not  given  thought  to  the  subject  and  experimented 
in  this  direction.  Fig.  697  illustrates  what  is  considered  a  beautiful  set 
of  continuous-gum  teeth,  of  what  may  be  called  the  English  type,  but 
capable  of  wide  modification  when  of  different  shades  and  ground  and 
mounted  with  reference  to  different  affes  and  other  individual  character- 


570 


CELLULOID  AND  ZYLONITE. 


istics.     The  teeth  are  represented  in  the  shape  given  to  them  by  the 
mould.     Fig.  698  shows  the  same  teeth  altered  in  expression  by  grinding 

Fig.  696. 


the  cutting  edges  and  squaring  the  mesial  surfaces,  which  gives  an 
appearance  of  age.  This  effect  can  be  carried  to  a  lesser  or  greater 
degree  to  suit  the  individual  case. 


Fig.  697. 


Fig.  698. 


\ 

If 

ft 

^ 

^ 

Fig.  699  is  a  mounted  set  from  the  same  mould,  and  may  repre- 
sent a  patient,  say,  of  the  Anglo-Saxon  type  twenty-five  years  of 
age — a  broad,  full,  well-developed  mouth,  clear-cut,  well-formed  teeth, 
with  no  enamel-blemishes.  In  this  set  has  been  retained  as  nearly  as 
possible  the  natural  formation  of  the  teeth  as  they  come  from  the  mould, 
to  show  a  young  mouth  and  to  make  the  variations  in  the  cases 
which  are  to  follow  more  distinctive.  The  superior  centrals  are  thrown 
out  slightly  by  the  underlapping  of  the  laterals.  A  slight  irregularity 
of  the  four  inferior  front  teeth  has  been  made  merely  to  avoid  con- 
ventional uniformity  and  to  disarm  suspicion  of  artificiality.  The 
jaws  are  shown  a  little  apart  in  order  to  display  the  cutting  edges  more 


MODIFICATIONS  IN  A  SET  OF  TEETH. 


571 


Fig.  699. 


clearly,  as  illustrated  by  Figs.  700,  701,  702,  703,  and  704.  They  repre- 
sent teeth  from  the  same  mould  as  those  of  Fig.  697,  and  have  been 
arranged  to  carry  out  this  series. 
These  cases  show  the  wide  range 
which  this  one  set  of  teeth  is 
capable  of  being  made  to  cover. 
Fig.  700  may  illustrate  the  mouth 
of  an  old  gentleman,  robust  and 
vigorous,  florid  face.  The  shading 
of  this  set  of  teeth  for  such  a  case 
is  perfect ;  the  abrasions  are  well 
marked,  and  the  irregularity  of  the 
lower  incisors  is  exceedingly  nat- 
ural. Fig.  701,  a  side  view  of  the 
same  case,  shows  the  irregularity 
even  better  than  the  front  view. 
The  loss  of  the  left  superior  first  bicuspid,  creating  the  gap  so  frequently 
seen  at  this  point  in  natural  dentures,  gives  greater  prominence  to  the 

Fig.  700. 


Fig.  701. 


cuspid,  making  it  seem  more  indicative  than  before  of  strong  animal 
passions.     Fig.  702  is  a  palatal  view  of  the  same  case. 

Fig.  703  shows  the  mouth 
of  an  individual  past  mid- 
dle life  and  the  recession 
of  the  gums  so  often  seen. 
The  effect  produced  by  the 
abrasion  of  the  lower  in- 
cisors and  the  separation  of 
the  centrals  is  exceedingly 
life-like,  and  well  calculated 
to  convey  the  impression  of 
original  ownership.  Fig.  704 
is    a    side  view  of  the   same 


case. 


No  one  who  will  take  the  trouble  to  compare,  or  rather  to  contrast, 
Figs.  699,  700,  and  703,  remembering  that  these  three  sets  of  teeth,  so 
radically  different  from  one  another,  were  made  from  teeth  out  of  the 


572 


CELLULOID  AND  ZYLONITE. 


same  mould,  can  fail  to  be  impressed  with  the  thought  that  the  blame  for 
the  "picket-fence"  conventional  dentures  generally  seen  in  the  mouths 

of  their  wearers  is  not  always 
to  be  laid  at  the  door  of  the 
manufacturer,  but  is  often  to 
be  attributed  to  the  want  of 
artistic  taste  in  those  who 
mount  and  arrange  them. 

Figs.  705  and  706  present 
practical  cases.  They  have 
been  chosen  on  account  of  their 
extreme  variation  of  character- 
istics, as  representative  of  cashes 
which  frequently  give  much 
trouble  and  annoyance  to  the 
practitioner  in  the  effort  to 
secure  as  natural  effects  as  he 
and  his  patients  would  desire. 
Fig.  705  is  taken  from  the  models  to  show  the  close  articulation 
resulting  from  the  prominent  alveolar  ridges  left  by  the  recent  extrac- 


FiG.  703. 


tion  of  the  teeth.     The  mouth  is  inclined  toward  what  is  termed 
lambdoid  type — V-shaped  arch,  etc. 

Fig.  704. 


the 


Fig.  706  represents  a  front  view  of  this  set  of  teeth.     It  is  important 
to  ascertain,  by  questioning  the  patient  without  letting  the  object  appear. 


SIDE   VIEW  FROM  THE  SAME  MOULD. 


57; 


as  to  what  the  natural  teeth  were  like,  regular  or  otherwise,  to  assist  the 
judgment  which  may  be  formed  from  the  face,  models,  etc.    Acting  on  the 


Fig.  705. 


Fig.  706. 


Fig.  707. 


mil  I  III  ii  h  u  received  and  the  idea 
I  1 1 1 1 1  1 1 1  •  I  I  he  facial  requirements, 
ill  I  I-  I -light  protrusion  of  the 
iij»|)  1  In  III  teeth,  a  slight  irregu- 
larity in  the  lower  teeth,  and  a 
little  overlapping  of  the  centrals 
of  the  upper  set  by  the  laterals. 
The  teeth  are  short  and  full,  the 
six  front  ones  being  set  di- 
rectly on  to  the  gums. 
Fig.  707  gives  a  side  view  of  the  same,  showing  more  clearly  why  it 
is  necessary  to  mount  the  upper  front  teeth  directly  upon  the  gums : 
First,  because  the  recent  ex- 
traction left  prominent  alveo- 
lar ridges :  second,  because 
the  patient  has  a  short,  thick 
upper  lip,  which  would  have 
been  made  more  prominent, 
rigid,  and  unnatural-looking 
had  the  teeth  been  set  out- 
side the  arch ;  third,  had  the 
lower  teeth  been  thrown  out 
sufficiently  to  meet  the  upper 
teeth,  if  these  were  mounted 
outside  of  the  arch  the  mouth 
would  have  presented  the  ap- 
pearance resembling  that  of  an 
herbivorous  animal,  and,  more- 
over, such  an  arrangement 
would  have  made  it  impos- 
sible to  hold  the  plates  in  position  during  mastication. 

Fig.  708  shows  the  models  of  a  patient  of  advanced  age,  in  which 
there  is  exactly  an  opposite  condition  of  things  from  the  preceding  one 
— a  rather  full  and  very  flat  jaw,  the  alveolar  ridges  having  been  much 
absorbed,  and  a  wide  articulation  being  required  to  restore  the  harmony 
of  the  features. 

Fig.  709  is  a  front  view  of  the  set  made  for  this  case.     It  is  peculiar. 


574 


CELLULOID  AND  ZYLONITE. 


for  many  reasons.     The  plate  was  made  of  gold,  the  teeth  attached  with 
celluloid.     The  teeth  are  of  medium  length,  some  of  them  represented  as 


Fig.  708. 


Fig.  709. 


Fig.  710. 


slightly  exposed  at  the  roots,  espe- 
cially the  cuspids.  A  slight  show 
of  irregularity  is  made  by  allowing 
the  laterals  to  rest  behind  the  cen- 
trals. The  cuspids  are  prominent 
and  have  rather  a  broad  front.  The 
buccal  prominences  were  meant  to  slightly  fill  out  the  cheeks  and  to 
protect  the  soft  parts  from   the  springs. 

Fig.  710  presents  a  three-quarter  view  of  the  same  case,  showing  the 

articulation  to  be  on  the  cutting 
edges  of  the  incisors,  in  imitation 
of  the  natural  teeth.  To  give  a 
more  natural  appearance,  the  second 
superior  bicuspid  was  left  out,  indi- 
cating a  lapse  of  time  since  its  loss 
by  representing  the  space  as  par- 
tially closed  up  by  the  moving  for- 
ward of  the  molars.  In  the  lower 
jaw  both  bicuspids  are  missing  on 
the  left  side,  while  the  molars  have 
moved  forward  until  stopped  by  the 
superior  first  bicuspids ;  the  lower 
cuspid  was  unable  to  move  backward  by  being  locked  between  the 
superior  cuspid  and  lateral.  This  illustration  shows  another  view  of 
the  "plumpers"  and  springs. 

Fig.  71 1  shows  partly  the  reason  for  the  use  of  springs ;  the  mouth 
.being  very  flat  (see  Fig.'  708),  hard,  and  dry,  aiforded  little  opportunity 
for  a  plate  to  be  held  by  atmospheric  pressure.  The  patient  was  nau- 
seated by  the  slightest  touch  upon  the  posterior  portion  of  the  hard 
palate,  and  too  irritable  to  allow  of  any  efforts  to  overcome  its  suscepti- 
bility. Being  an  epicurean,  and  thoroughly  convinced  that  with  an 
ordinary  plate  he  could  not  taste  his  food,  some  other  method  had  to 
be  resorted  to.  The  old  method  of  constructing  a  very  narrow  plate 
for  the  upper  ridge,  sustained  by  spiral  springs,  was  therefore 
adopted — a  happy  expedient  in  this  case.      The  engravings    show  the 


CAUSES  OF  SPACES  BETWEEN  THE  NATURAL   TEETH.       575 


manner  of  applying   the    springs,  and  the   shields   for   protecting  the 
soft  parts  from  irritation  by  them. 

In  Fig.  711  are  seen  the  abraded  cutting  edges  stained,  the  irregu- 
larities, the  spaces  left  by  the  lost 

teeth,  the  relation  of  the  teeth  to  Fig.  711. 

each  other,  and  the  shapes  of  the 
plates.  The  lower  molars  are  lean- 
ing toward  each  other  across  the 
tongue,  the  incisors  inclined  for- 
ward, etc. — all  tending  to  make  the 
case  as  natural  and  comfortable  in 
the  mouth  as  possible. 

The  causes  of  spaces  between 
the  natural  teeth  may  here  be 
briefly  considered.  In  Dr.  James 
W.  White's  little  work  entitled  The 
Mouth  and  the  Teeth,  p.  41,  the 
statement  is  made  that  "  the  teeth 
in  man  are  arranged  in  close  con- 
tact, without  intervening  spaces, 
affording  each  other  mutual  support 
after  the  manner  of  staves  in  a  bar- 
rel. Being  set  without  interspaces 
on  a  curved  line,  it  follows  that 
their  outer  surfaces  are  wider  than 

tlie  inner."  If  this  is  correct  (as  in  ninety-cases  out  of  a  hundred  it  is), 
why  should  dentists  and  manufacturers  persist  in  producing  what  is  un- 
natural and  disfiguring  when  cor- 
rect models  are  so  easily  pro- 
cured ? 

Fig.  712  is  a  front  view  of  a 
case  designed  to  show  the  causes 
for  interspaces,  though  this  partic- 
ular cut  does  not  do  so.  The  teeth 
are  full  and  rounded,  presenting  a 
pleasing  effect.  The  laterals  lap- 
ping over  the  centrals  are  broad, 
accounting  in  part  for  their  irreg- 
ularity. 

Fig.  713  is  a  side  view  of  the  same  case.  Here  are  seen  several 
spaces  developed  through  the  loss  of  teeth  above  and  below.  In  the 
superior  maxilla  the  second  bicuspid  is  absent,  while  the  first  and  second 
molars  have  moved  forward  and  the  first  bicuspid  settled  backward,  ad- 
justing themselves  to  easy  occlusion,  and  nearly  filling  up  the  space  left 
by  the  lost  tooth,  but  at  the  same  time  creating  new  interspaces  be- 
tween the  first  bicuspid  and  cuspid  and  first  and  second  molars.  The 
lateral  is  prevented  from  working  backward  by  the  inferior  cuspid. 
In  the  lower  maxilla  the  first  molar  has  been  lost,  the  second  has  moved 
slightly  forward,  locking  between  the  superior  first  and  second  molars, 
while  the  second  inferior  bicuspid  has  settled  backward — probably  from 
the  force  of  mastication — occluding  comfortably  with  the  first  superior 


Fig.  712. 


576 


CELLULOID  AND  ZYLONITE. 


bicuspid  and  molar,  but  leaving  another  space  between  the  first  and 
second  inferior  bicuspids.  In  this  mouth  are  both  crowding  and 
interspaces,  and   causes  for  both. 


Fig.  713. 


Fig.  714  illustrates  another  frequent  cause  of  interspaces — namely, 
locking  of  the  teeth  through  occlusion.  In  this  case  nearly  all  the 
teeth  bear  firmly  against  each  other  for  support,  and,  as  shown  in  the 

cut,  have  almost  a  perfect  occlusion 
from  the  cuspids  back,  though  the 
point  claiming  special  attention  is 
the  interspaces  on  either  side  of 
the  superior  cuspid,  which  is  slightly 
turned  on  its  axis  and  is  locked  be- 
tween the  cusps  of  the  cuspid  and 
first  bicuspid  of  the  lower  maxilla, 
precluding  a  possibility  of  its  move- 
ment either  forward  or  backward 
without  artificial  interference.  The 
first  superior  bicuspid  cannot  come 
forward,  owing  to  its  nice  occlusion  with  the  first  and  second  inferior 
bicuspids ;  the  superior  lateral  cannot  move  backward,  although  crowded 
and  overlapping  the  central,  as  it  is  forced  forward  and  retained  in  posi- 
tion by  the  cusp  of  the  inferior 

cuspid.       So   here,   again,   the  ^^^-  '^^^' 

interspaces  are  caused  by  mal- 
position. 

The  art  of  arranging  arti- 
ficial teeth  as  at  present  prac- 
tised in  this  country  is 
governed  by  the  irregularities 
found  in  nature  as  results  of 
the  amalgamation  of  races.  In 
many  cases  there  is  likely  to  be 
an  inequality  of  development 
between  the  upper  and  lower 
maxillary  bones,  one  jaw  par- 
taking of  the  characteristics  of  the  father,  the  other  of  the  mother.  The 
result  generally  is  overcrowding  or  irregularity,  but  sometimes  cases  are 


'^~/=iww5>v.~' 


y^\-,^^ 


/ 


.vi^%:-iv|r 


>^: 


; 


SIDE   VIEW,   DISPLAYING    THESE  DEFECTS. 


577 


Fto.  716. 


found  such  as  shown  in  Fig.  715.  Here  is  a  well-developed  inferior 
dental  arch,  with  proportionately  well-developed  teeth,  characteristic  of 
one  parent,  while  in  the  superior  dental  arch  the  teeth  resemble  those 
possessed  by  the  other  parent,  and  are  too  small  in  proportion  to  the  size 
of  the  jaw.  The  result  is  interspaces  between  nearly  all  of  the  teeth  in 
the  superior  dental  arch. 

Fig.  716  is  a  side  view,  displaying  these  defects,  the  cusps  of  the 
superior  falling  in  between  those  of  the  inferior  teeth. 

The  few  preceding  cuts  serve  to  illustrate  how  well  zylonite  or 
celluloid  is  adapted  to  meet  the  requirements  as  a  base  for  artificial 
dentures,  and  it  must  be  admitted  that,  so  far  as  experience  has  gone, 
this  material  in  combination  with  single  teeth  and  mounted  on  metal- 
lic lining  has  given  as  much  satisfaction  as  any  other  base.  No  op- 
portunity of  testing  the  zylonite 
under  the  microscope,  as  has  been 
done  with  celluloid  proper,  has 
presented,  but  sufficient  has  been 
learned  of  its  qualities  to  indicate 
that  it  is  superior  in  every  partic- 
ular as  the  two  are  now  presented 
to  the  profession.  The  color  is 
better,  and  always  uniform  :  cel- 
luloid is  not  uniform  in  color, 
sometimes  running  into  a  very 
objectionable  greenish  tinge.  By 
comparing  the  two  it  will  be  no- 
ticed that  there  is  a  translucency  or  depth  to  the  surface  of  the  zylonite 
not  found  on  the  celluloid,  which  has  a  thoroughly  dead  surface.  The 
celluloid  has  a  tendency  to  scale  or  disintegrate  unless  the  blanks  are 
very  carefully  selected.  This  is  not  the  case  with  zylonite  ;  nor  has  any 
tendency  to  soften,  or  "wash  out,"  from  about  the  pins,  as  observed  with 
celluloid. 

The  zylonite  company,  having  benefited  by  the  experience  of  other 
manufacturers  of  this  material,  has  attained  an  excellence  in  the  manu- 
facture— first,  of  the  dinitro-cellulose,  which  is  so  delicate  a  process ; 
secondly,  in  the  perfect  admixture  of  the  necessary  ingredients  to  make 
the  compound,  resulting  in  an  article  that  is  uniform  under  all  vicis- 
situdes of  weather,  possessing  great  resiliency,  beauty,  and  diminished 
inflammability. 

37 


CHAPTER    Xyil. 

THE  TEMPERAMENTS  AND  THE  TEMPERAMENTAL  CHA- 
RACTERISTICS OF  THE  TEETH  IN  RELATION  TO  DENTAL 
PROSTHESIS. 

By  Alton  Howard  Thompson,  D.  D.  S. 


"  Temperament/'  says  Dr.  D.  H.  Jacque/  "  is  a  constitutional  con- 
dition produced  by  the  mixing  in  different  ^proportions  of  various  physi- 
cal elements.  The  functions  of  life  are  not  performed  in  all  persons  with 
the  same  degree  of  force  or  rapidity.  These  diiferences  are  the  results 
and  indications  of  what  is  called  temperament,  the  corpori  habitus  of  the 
ancients.  It  is  by  the  combination  of  these  constitutional  elements  in 
various  proportions  that  the  body  is  tempered,  the  predominating  element 
determining  the  prevailing  temper  or  temperament,  and  the  others  the 
modifications  which  may  be  present.  A  particular  temperament  is  the 
result  of  the  preponderance  of  one  of  these  elements  over  all  the  others. 
The  ancients,  assuming  the  possibility  of  these  elements  all  being  equal 
in  a  given  case,  were  accustomed  to  speak  of  the  temperamentum  tem- 
peratum,  the  temperable,  harmonious,  or  balanced  temperament ;  but  it 
is  scarcely  to  be  conceived  of  a  single  instance  in  the  human  species  in 
which  there  is  perfect  equilibrium  in  all  parts,  although  near  approach 
to  this  condition  may  be  found. 

"  It  is  evident  that  in  an  ultimate  analysis  the  temperaments  must  be 
as  numerous  as  the  individuals  of  the  human  race — no  two  persons, 
probably,  having  precisely  the  same  physical  organization  or  the  same 
proportion  of  each  elemental  ingredient  of  the  compound  structure  in 
which  each  lives,  moves,  and  has  a  being. 

'-  It  is  essential  for  practical  purposes,  therefore,  to  reduce  these 
numberless  individual  peculiarities  to  their  simplest  elements,  and  group 
together  such  persons  as  resemble  each  other  in  certain  particulars  or 
who  have  a  similar  organization.  To  this  end  writers  on  the  subject 
have  generally  considered  the  temperaments  under  from  three  to  five 
general  heads,  which  are  subdivided." 

The  ancients  first  observed  the  differences  of  bodily  action  and  func- 
tional activity  which  distinguish  individuals,  and  four  temperaments, 
founded  on  constitutional  conditions,  were  recognized  and  described  by 
Hippocrates.  The  temperaments,  according  to  his  theory,  depended 
upon  what  were  then  known  as  the  four  primary  components  of  the 
human  body — the  blood,  the  phlegm,  the  "yellow  bile,  and  the  black 
bile."  Persons  in  whom  the  blood  predominates,  he  said,  have  the 
sanguine  tempera^nent ;  if  phlegm  be  in  excess,  the  phlegmatic  temp)era- 
ment ;  if  yellow  bile,  the  choleric  ;  and  if  black  is  in  excess,  the  melan- 
cholic temperament.  This  was  the  original  classification,  and  has  influ- 
enced writers  and  students  more  or  less  in  all  systems  of  description 
down  to  our  own  times. 

"  The  doctrines  of  Hippocrates  and  the  ancient  physicians  were  often 

^  The  Temperaments,  etc.,  Dr.  D.  H.  Jacque,  Fowler  &  Wells,  1878,  p.  30  et  seq. 
678 


TEMPERAMENT.  579 

discussed,  but  never  greatly  modified,  until  the  advances  in  physiology 
and  humoral  pathology  in  comparatively  recent  times  rendered  their 
defects  too  obvious  to  be  overlooked ;  and  even  then  the  same  classifica- 
tion and  general  nomenclature  were  generally  adhered  to.  At  a  later 
date  Dr.  Gregory  added  to  the  four  temperaments  of  the  ancients  a  fifth, 
which  he  called  the  nervous  temperament.  The  ancients,  and  the 
modern  writers  following  them,  were  accustomed  to  look  upon  the  tem- 
peraments from  a  merely  physiological  or  pathological  standpoint,  and 
but  little  was  said  or  known  of  the  reciprocal  influences  of  mental  and 
physical  qualities  and  states." 

Dr.  Spurzheim's  classification  is  that  upon  which  later  systems  were 
founded:  (1)  the  lymphatic;  (2)  the  sanguine;  (3)  the  bilious;  and 
(4)  the  nervous  temperaments,  which  are  determined  by  the  presence 
of  the  lymphatic,  the  sanguine,  the  bilious,  or  nervous  elements.  Some 
of  these  Dr.  Jacque  considers  more  or  less  pathological,  three  only  being 
perfectly  normal  bodily  conditions ;  and  two,  the  lymphatic  and  the  ner- 
vous, are  pathological  or  diseased.  But  they  are  none  the  less  real, 
though  being  aberrant  or  unnatural.  Such  states  of  the  constitution  are 
far  too  common  to  be  ignored,  and  must  be  taken  into  account.  Dr. 
Jacque  proposed  a  later  classification  (in  which  he  eliminated  the  patho- 
logical and  abnormal  conditions)  which  he  thought  was  simpler  and  more 
natural.  He  included  under  three  heads  all  the  various  normal  condi- 
tions.    These  he  named — 

(1)  The  motive  or  mechanical  system  ; 

(2)  The  vital  or  nutritive  system  ;  and 

(3)  The  mental  or  nervous  system. 

These  are  divided  into  several  branches,  which  include  all  the  organs 

and   dominate  all  the  functions  of  the  physical  man "  First, 

the  bony  framework  bound  together  by  ligaments  and  overlaid  with 
bundles  of  muscular  fibres,  by  means  of  which  its  parts  are  moved 
and  locomotion  produced  ;  second,  the  vital  or  nutritive  system,  whose 
principal  masses  lie  in  the  chest  and  abdomen,  and  consist  of  the  lymph- 
atics, blood-vessels,  and  glands  performing  the  functions  of  digestion, 
secretion,  circulation,  etc ;  and  third,  the  mental  or  nervous  system, 
having  its  principal  seat  in  the  cranium,  but  extending  itself  in  ramifi- 
cations through  every  part  of  the  body  and  furnishing  the  medium  of 
sensation  and  volition." 

A  classification  may  be  adopted  which  will  include  these  under  the 
older  headings,  with  the  addition  of  the  pathological  temperaments,  as 
he  calls  them,  which  are  equally  important  and  entitled  to  study  and 
consideration. 

For  a  diagnosis  of  the  temperaments  it  will  be  best  to  present  their 
leading  characteristics  in  tabulated  form,  for  convenience  of  reference. 
The  groupings  of  indications  under  various  headings  will  facilitate  the 
study  of  an  individual  under  observation.  The  indications  are  those 
given  by  Spurzheim,  amplified  by  Dr.  Jacque's  wise  criticisms  and 
learned  observations. 

To  this  is  added  a  table  of  Dr.  Jacque's  later  system  of  classification, 
by  way  of  illustration  and  comparison. 

After  that  a  table  of  the  ordinary  combinations,  and  then  tables  of 
the  temperamental  characteristics  of  the  teeth. 


580 


THE  TEMPERAMENTS,  ETC. 


TEMPERAMENT. 


581 


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582 


THE  TEMPERAMENTS,  ETC. 


f^  S  d 

(Sg'2 

d  S 

Eyes    dark, 
large,      lus- 
trous,      and 
expressive  ; 
sometimes 
deep  blue. 

Eyes    dark- 
brown       or 
gray. 

Large,  dark, 
or  dark  gray ; 
weak  and  ex- 
pressionless. 

d  >^ 
>  a) 

o 

•^  Oj  > 

«2a 

Black     or 
dark,     coarse 
or  curly;  not 
usually  abun- 
dant ;     beard 
full;     eye- 
brows straight. 

Dark,  wavy, 
and      luxuri- 
ant, and  fine 
in      texture ; 
beard     full; 
eyebrows 
arched. 

Hair    and 
beard      dark, 
full,       and 
wavy ;      e  y  e  - 
brows  straight 
and  heavy. 

Dark,  moist, 
straight; 
beard    heavy 
and  dark;  eye- 
brows straight 

Dark ;  decid- 
edly   curly; 
beard    sparse 
and  irregular. 

Rather 
smooth ;  little 
color,  or  dark 
and     yellow- 
ish. 

Skin  smooth ; 
so  ft       and 
creamy,  vary- 
ing   to    rosy 
olive. 

Rather 
rough     and 
and  dark-col- 
ored,     with 
tendency     to 
ep  h  elides, 
moles,  etc. 

3  aj 

03 

Inclined  to 
dark,     and 
often    sallow 
and  pallid. 

i 

o 

Rather    an- 
gular ;      high 
cheek-bones ; 
nose      large ; 
lips  full  and 
large. 

Cheeks  full ; 
forehead 
large ;    jaws 
large     and 
round ;     chin 
heavy;  mouth 
large ;      lips 
full  and  red. 

Face     full ; 
fore  he  ad 
large ;      jaws 
and      chin 
round ;  mouth 
lar^e ;      lips 
thin       and 
bluish. 

Cheek-bones 
large ;      fore- 
h  e  a  d    full; 
jaws     large 
and     square ; 
mouth  large; 
lips  thin. 

High  cheek- 
bones ;     fore- 
head     large ; 
jaws      small, 
and       chin 
small    and 
pointed. 

1 

d' 
.2 

d 
2 
3 

Full  in  both 
arterial     and 
venous      sys- 
tems ;      heart 
strong      and 
active. 

Strong   and 
dark ;      heart 
quick    and 
full. 

Full,  but  not 
red  or  vigor- 
ous ;  heart  ir- 
regular. 

Weak     and 
thin,  or  dark ; 
heart   irregu- 
lar. 

Thin     and 
dark     blood ; 
heart   irregu- 
lar and  weak, 
or  active  and 
cord-like 
pulse. 

d 
o 

d 

6 

Disposed  to 
irregularity; 
mostly  sharp 
and  angular. 

Broad  shoul- 
d  e  r  s  ;      full 
chest ;      and 
strong,  round 
limbs. 

Well-round- 
ed  and  in- 
clined to  ful- 
ness   in    wo- 
men. 

d  aj  M 

o3  w  (D 

o  o 

1 

M 
1— 1 
1— i 

'^d 

d  ft 
o  o 

1^ 

Full       and 
well-develop- 
ed,   but    not 
graceful. 

Knotty    and 
hard ;     modi- 
fled    by    san- 
guine round- 
ness. 

It 
ajpl 

"5 

Wiry    and 
cord-like ;    or 
may  be   rath- 
er    full    and 
strong. 

^  ai 

d0 

O  ft 
Oi  o 
m'3 

Strong   and 
heavy ;    head 
square;   jaws 
large. 

Wide     and 
strong,  bones 
large ;  articu- 
lation full. 

Rather  coarse 
and      irregu- 
lar ;   articula- 
tions large. 

Large     and 
coarse,    with- 
out   strength 
or  grace. 

2g.3 
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aj 

d 

Above  aver- 
age size. 

>°   . 

O       aj 
cd    -d 
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TO  -4-s 

^    CD 

o  >.  5 

> 

03 

<p  a5 

C  m 

<  bo 
03 

^  S  aj 

^.Sd 

OS 

m 

The  combin- 
ing of  arterial 
and  venous  or 
biliary    ele- 
ments,    with 
predomi- 
nance of  the 
first. 

Slight    pre- 
dominance of 
the  bilious 
element,  with 
sanguine 
modification. 

Lymphatic 
and      bilious 
elements, 
lymphatic 
predominat- 
ing. 

Bilious  and 
lymphatic 
elements,  bil- 
ious predom- 
inating. 

Nervous  and 
bilious     e  1  e  - 
ments,      the 
former      pre- 
dominating. 

o 

d 

C~bO   . 

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TEMPERAMENT. 


583 


Small;  hazel 
to    light,     or 
dark  brown  to 
black. 

4J    t-i 

,a  03 
.^.2 
V^  o 

•  -  ^ 
o  o 

S  2  o 

Blue  or  gray; 
full;      large 
and     expres- 
sive. 

>>o 

gap 

bE_2 

.KS-d 

0  ci 

Large,  light- 
colored  ;  with 
placid  expres- 
sion. 

Variable, 
light  or  dark, 
sometimes 
light    hair 
with       dark 
eyes,   or    vice 
versa. 

Dull,     gray- 
ish;  inclined 
to    green    or 
hazel  in  color. 

Ranges  from 
dark-brown  to 
dark      red; 
beard  dark  to 
red;  eyebrows 
arched. 

Hair   and 
beard    sandy 
to    red.     full 
and    wavy; 
eyebrows 
light      and 
arched. 

Light     and 
curly,    but 
fine,      with 
tendency     to 
baldness; 
beard  scanty ; 
eyebrows 
light     and 
arched. 

Blond    or 
light      chest- 
nut, inclined 
to  curl ;  beard 
medium ;  eye- 
brows   dark 
and  arched. 

Dark  to  light 
chestnut, 
sometimes 
luxuriant; 
beard  full. 

Variable    in 
color ;  slight- 
ly       wavy; 
beard  light. 

Light  in  col- 
or;   slight  in 
quantity;  eye- 
brows straight 

-a  c 
a*^ 

O  m 

.is)  O  O 

Hpjg 

P. 

fe  a  a 

Fair    and 
smooth,  with 
tendency     to 
ruddiness. 

Very  smooth 
and  fair,  pink- 
ish,  inclined 
to       florid; 
sometimes 
freckled. 

Soft     and 
smooth;  ivory- 
white  to  pink 
complexion. 

Dark      to 
light ;       usu  - 
ally    pallid, 
with    little 
color. 

Light,    pal- 
lid,    coarse 
skin,  inclined 
to  blotches. 

Cheek-bones 
high      and 
prom  i  n  e  n  t ; 
lower      face 
thin  and  con- 
tracted. 

Cheeks  full ; 
fore  head 
round ;    jaws 
and  chin  well 
shaped. 

Fo  r  e  h  e  a  d 
high       and 
broad ;  cheek- 
bones promi- 
nent ;     lower 
face       rather 
thin :      chin 
small. 

Face  round ; 
cheeks     full ; 
jaws      large ; 
mouth  shape- 
ly,   and    lips 
full  and  red. 

Large      and 
full ;  forehead 
high ;     jaws 
and       chin 
round      and 
full ;  lips  full. 

Face  round ; 
fore  h  ead 
large;  cheeks 
full;     lips 
thick. 

Face     thin, 
or    full    and 
heavy ;     fore- 
h  e  a  d    high 
and  bulging; 
mouth  weak; 
lips  thin. 

^?> 
^.a 

«o- 
?  OS 

Blood    red 
and      bound- 
ing ;  heart  ac- 
tive. 

Blood     full, 
but  light-col. 
ored ;      heart 
active. 

Good    me- 
dium   as    to 
blood,    color, 
and  heart  ac- 
tion. 

Blood    thin 
and       full; 
heart    weak ; 
pulse   irregu- 
lar. 

Blood    light 
and     thin; 
heart      weak 
and  nervous. 

■d  o 
1^- 

"  o3  o 

«'^§ 
|^.§ 
bD^  o 

S|2 
§3 

Well-mould- 
ed, fine  limbs 
and     broad 
shoulders. 

Rather  slight, 
but      s  0  m  e- 
times  full  and 
rounded. 

Round  and 
shapely;   full 
and  graceful, 
but   disposed 
to  obesity. 

Inclined  to 
irregular  ful- 
ness,    often 
corpulent. 

eS  a  * 
ad 

^   !-.  0) 

c3    i: 

d     ••-* 

m-d-^ 

P  a  a 

03  .Q 

-d  a 

d  0  oi 

a    « 

Ojj-d 
«"Sa 

CO  ci 

g^ 

PT;  ■ 

S  o  o 

03  P-ft 

a'd2 

02  d  a) 

03  > 

Full   and 
well  -  shaped ; 
strong      and 
g  r  a  c  e  f  u  1  in 
movement. 

11^ 

■3*2  0 
a  0  !h 
a  op 
m  03  ho 

Fairly  well- 
developed, 
and  rounded ; 
rather     s  0  f  t 
and   medium 
in  activity. 

Full,  but  not 
hard,    active, 
but    not    en- 
during. 

Rather  full, 
but  moderate- 
ly strong  and 
active. 

o'a 
>-^ 
a^      J 
-d    .-^ 

^aa 

Small,  weak, 
and  irregular. 

Strong   and 
shapely ;     ar- 
ticulations 
finely  propor- 
tioned. 

03.^. 
^  oi  03 

•3  .-a 

as.2 

•1-1  ra 

Bones  good 
and    well-de- 
veloped ;     ar- 
ticulations 
well-shaped. 

Bones    long 
and  well -de- 
veloped ;     ar- 
ticulations 
shapely. 

Usually 
large,     with 
coar  s  e-n  e  s  s ; 
articulatio  n  s 
full,    but    ill- 
shaped. 

Bones   mod- 
erate in  size; 
of  low  struc- 
ture. 

a  . 

a> 
c„M 

J  aj 

5 

TO    tS3 

^  c3  fcH 

lis 

2^ 

u 

0 

Oo3 

«.d.S 

S-a 
0  0 

f-t  bo 

Above  aver- 
age   in    size ; 
inclined  to  be 
tall. 

Stature  very 
irregular,  but 
usually  above 
average. 

0 

0  ,. 
22 

0  0) 

0 

Bilious  and 
nervous    ele- 
ments,     the 
former     pre  - 
dominating. 

Nervous  and 
sanguine  ele- 
ments ,       the 
nervous    pre- 
dominating. 

Sanguine 
and    nervous 
elements,  the 
sanguine  pre- 
dominating. 

Lymphatic 
and  sanguine 
elements,  the 
first  predomi- 
nating. 

Sanguine 
and  lymphat- 
ic,   the    san- 
guine       pre- 
dominating. 

Lymphatic 
and    nervous 
elements,  the 
first  predomi- 
nating. 

Nervous  and 
lymphatic 
elements,  the 
nervous    pre- 
dominating. 

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»o 
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0 

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p.  >  0 

584 


THE  TEMPERAMENTS,  ETC. 


THE  BINARY  TEMPERAMENTS.  585 


The  Binary  Temperaments. 

The  basal  temperaments  are  never  found  alone,  but  usually  in  com- 
bination with  other  elements  which  modify  the  original  base.  The  com- 
pounds are  generally  binary — i.  e.  a  base  with  one  prominent  modifying 
factor.  This  combination  is  called  a  binary  temjiei'ament.  They  are 
named  in  accordance  with  the  base  and  the  most  important  modifying 
element.  Thus,  the  sanguino-bilious  means  that  the  sanguine  tempera- 
ment is  most  prominent,  and  the  modifying  element  is  the  bilious. 
Other  elements  may  be  present,  but  these  cannot  always  be  diagnosed 
with  certainty. 

The  table  of  binary  compounds  (on  page  582)  is  based  on  the  indica- 
tions given  by  Dr.  Ives.^ 

By  comparison  of  this  table  with  the  preceding  one  of  temperamental 
indications  the  proper  teeth  can   be  readily  selected  ;  i.  e.  having  diag- 
nosed the  binary  compound  of  the  person  under  observation,  turn  to  the 
table  of  temperamental  characteristics  of  the  teeth  which  accompany  that 
compound,  and  select  the  proper  mould  and  color,  and  arrange  them  ac- 
cording to  the  indications  given.     This  will  give  a  more  artistic  appear- 
ance to  prosthetic  work  than  it  usually  attains.   As  Dr.  J.  W.  White  said  •} 
"  What  is  needed  is  such  an  appreciation  of  the  law  of  correspondence 
that  the  dentist  can  cipher  out,  as  by  the  rule  of  three,  the  character  of 
teeth  required  in  the  case  of  an  edentulous  mouth  with  the  same  precision 
that  the  comparative  anatomist  can  from  a  single  bone  indicate  the  ana- 
tomical structure  of  the  animal  to  which  it  belonged.    The  probability  is 
that  in  many,  perhaps  in  most,  of  the  cases  of  artificial  dentures  the  fault 
is  not  in  the  carelessness  or  indifference  of  the  dentist,  but  in  his  failure 
to  recognize  the  requirements  of  temperaments.    A  certain  family  resem- 
blance to  each  other  in  a  set  of  teeth  is  considered  essential,  but  the 
adaptability  of  the  set  as  a  whole  to  a  given  case  should  be  esteemed  of 
even  greater  importance.     A  set  of  teeth  in  which  not  only  the  relative 
length  and  breadth,  but  every  line  and  curve,  characterizes  it  as  belonging 
to  a  certain  temperament  may  be  made  of  a  coloi"  never  found  in  nature 
connected  with  such  forms.    Thus  are  seen  repeatedly  such  incongruities 
as  the  association  of  the  massive  tooth  of  the  bilious  temperament  with 
the  pearl-blue  color  of  the  nervous  temperament,  and  the  long,  narrow 
tooth  of  the  nervous  temperament  with  the  bronze-yellow  color  never 
seen  in  any  but  those  of  a  bilious  temperament — showing  that  the  laws 
of  correspondence  had  not  been  sufficiently  observed.    The  first  study  of 
the  dentist  when  proposing  to  replace  a  lost  denture  should  be  how  to 
restore  the  natural  appearance   of  his  patient,   and   this    can    only  be 
effected  through  an  appreciation  of  the  temperamental  characteristics  and 
the   law  of  correspondence  or  harmony.     Age  and  sex  may  somewhat 
modify  the  requirements  in  a  given  case,  but  the  basal  fact  on  which  he 
should  proceed  is  temperament.    A  failure  to  recognize  its  demands  will 
result  in  failure  from  an  sesthetic  standpoint.     A  knowledge  of  the  dis- 
tinguishing characteristics  of  the  various  temperaments  and  the  style 
of  teeth  which  conform  to  nature's  type  in  the  physical  organization 
marks  the  difference  between  the  dental  mechanic  and  the  dental  artist." 

^  Amer.  Si/st.  of  Dent. 


586 


THE  TEMPERAMENTS,  ETC. 


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THE  BINARY  TEMPERAMENTS. 


587 


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to  mal- 
position. 

Well  set, 

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clined  to 
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Well  ar- 
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roomy,  and 
often 
sp  a  c  e  d , 

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disposed 
to  spacing. 

Rather    ir- 
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disposed  to 
crowding. 

03 

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marked 
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shape; 

round 
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well- 
shaped. 

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b  r  i  1 1  i  ant, 

and 

strong. 

Smooth, 
bright,  and 

trans- 
lucent. 

a« 

CO  pj 
03 

Smooth, 

but  rather 

opaque. 

Smooth 
and  clear, 
or  dull  and 

rough. 

Smooth, 
soft,  and 

trans- 
lucent. 

rt(D  pi 
02      .S 

OS  n 

CO  0) 

Soft    and 

poor 
in  quality. 

■S'«g 

J^  PI 
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Soft,  weak, 

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and  sensi- 
tive. 

Rich 
cream  -  col- 
or  to  blu- 
ish. 

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03.P! 

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r-    U 
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shaped  and 

moulded; 

narrow 

necks. 

PI  . 

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round ; 

angles 

rounded. 

a  ^^ 

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CO  PS  !-i 
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(9) 
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ph atico- 
san- 
guine. 

(10) 

Sanguo- 

lym- 
phatic. 

(H) 

Lym- 

phatico- 

nervous. 

^   6  .  ci 
^       ft 

CHAPTER    XVIII. 

ARTIFICIAL  CROWNS. 

By  H.  H.  Burchard,  M.  D.,  D.  D.  S. 


Fig.  717. 


When  the  crowns  of  teeth  have  suffered  such  extensive  loss  of  sub- 
stance that  restoration  by  means  of  filling  material  is  inadvisable^  the 
restoration  is  an  operation  of  prosthetic  dentistry. 

The  term  "artificial  crown,"  as  technically  applied,  includes  only 
such  devices  as  are  made  in  the  dental  laboratory  and  subsequently  set 
as  a  single  piece  upon  a  prepared  root  or  remnant  of  tooth.  The  pieces 
known  as  "  partial  crowns  "  are  also  included  in  this  category. 

The  first  example  of  crown  substitution,  mounted  according  to  the 
principles  governing  contemporary  crown  operations,  was  the  setting  of  a 
crown  of  a  natural  tooth  upon  a  prepared  root,  the  support  being  afforded 

by  a  post  extending  from  the  enlarged  pulp- 
chamber  of  such  a  crown  into  the  enlarged 
canal  of  the  root. 

The  mechanical  principle  involved  in  this 
mode  of  support  has  had  constant  applica- 
tion.    The  next  variety  of  crown  employed 
is  that  of  porcelain,  the  post  support  being, 
as  in    the    preceding  form,  a    hickory  post 
(Fig.  717).     Subsequently  metallic  posts  were  substituted  for  those  of 
wood,  and  this  variety  is  the  typal  form  of  one  of  the  two  great  classes 
of  crowns  in  present  use. 

Metallic  crowns  resembling  those  of  the  present  day  were  employed 
early  in  the  present  century. 

Classes  of  Crowns. 

All  of  the  varieties  of  artificial  crowns  may  be  divided  into  two  great 
classes,  according  to  their  means  and  modes  of  support.     The  first  class 


Fig.  718. 
B  C 


Fig.  719. 
A  B 


includes   all  of  those   crowns  which  depend  for   fixation  upon  a  post 
anchored  in  an  enlarged  pulp-canal  (Fig.  718).     The  second  class  in- 


588 


ANATOinCAL  RELATIONS.  589 

eludes  those  which  have  their  retention  secured  by  raeans  of  a  continuous 
band  encircling  the  neck  of  the  root  (Fig.  719). 

Class  1  is  subdivided  into  two  orders  :  First,  those  in  which  the  post 
is  an  integral  part  of  the  artificial  crown,  being  baked  in  it  or  soldered 
to  it  (Fig.  718,  A  and  B) ;  second,  those  in  which  the  post  is  firmly 

Fig.  720. 


Class  1,  Order  1. 


anchored  in  the  pulp-canal,  as  a  primary  measure,  and  upon  this  support 
the  crown  itself  is  fixed  as  a  second  operation  (Figs.  718,  C-721,  722). 

A  sub-order  includes  the  collar  and  post  crown  (Fig.  718,  D),  the 
band  encircling  the  root  acting  as  a  subsidiary  support  to  the  root,  pro- 
tecting it  against  fracture,  the  post  being  the  retentive  device  proper. 

Fig.  722. 


Class  1,  Order  2. 


Class  1,  Order ; 


All  of  the  artificial  crowns  in  present  use  will  be  found  to  be  a 
variety  or  some  modification  of  one  of  these  classes. 

Each  variety  is  designed  and  fitted  to  meet  definite  indications,  and 
the  application  and  choice  of  variety  are  determined  by  the  anatomi- 
cal, physiological,  and  pathological  condition  of  the  root  to  be  crowned 
and,  it  may  be,  of  the  surrounding  parts. 

Anatomical  Relations. 

The  first  consideration  is  the  position  of  the  root  to  be  crowned ;  and 
the  second,  its  form.  Its  position  includes  the  class  of  tooth,  whether  it 
be  an  incisor,  cuspid,  bicuspid,  or  molar  ;  next,  its  relative  position  to  its 
neighbors  and  to  its  antagonists,  and  what  will  be  the  relations  of  the 
artificial  crown  in  these  particulars. 

Each  class  of  tooth  has  a  definite  office  to  perform,  and  there  is  in- 
volved in  the  performance  of  its  function  an  amount  and  variety  of 
stress  governed  by  the  position  of  the  tooth — i.  e.  the  class  to  which  it 
belongs.  This  demands  in  the  supporting  structures  of  the  crown  and 
root  sufficient  resistance  to  secure  the  integrity  of  the  crown  and  root  in 
the  performance  of  their  normal  functions. 

Incisors  by  their  positions  and  forms  are  designed  to  receive  and 
resist  stress  in  one  direction,  that  tending  to  force  them  outward. 

Cuspids  in  their  normal  relations  receive  stress  in  two  directions  : 
two  forces  act  at  an  angle  upon  the  axis  of  the  tooth,  and  the  resultant 
of  these  forces  is  a  line  outward. 


590  ARTIFICIAL  CROWNS. 

Bicuspids  are  subjected  to  three  stresses — vertical,  outward,  and 
inward ;  the  relative  amounts  of  stress  are  in  the  order  given.  The 
amount  of  the  outward  and  inward  stress  is  governed  primarily  by  the 
lengths  of  the  buccal  and  palatal  or  lingual  cusps  ;  the  vertical  stress,  by 
the  area  of  the  occlusion  surface. 

Molars. — The  vertical  stress  is  greatest,  and  in  the  direct  ratio  of  the 
extent  of  masticating  surfaces ;  the  lateral  stress  is  governed  by  the 
lengths  of  the  cusps. 

Artificial  crowns  should  be  made  of  varieties  to  meet  and  resist  the 
several  directions  of  stress. 

The  line  of  greatest  mechanical  resistance  in  any  root  is  in  its  ver- 
tical axis,  and  is  the  only  line  of  stress  which  does  not  tend  to  mechan- 
ically displace  the  tooth.  As  to  the  vital  resistance  of  a  root,  this  rule 
is  but  partially  true,  for  roots  appear  to  rebel  against  stress  in  any  other 
direction  than  that  due  to  their  normal  anatomical  positions. 

In  normal  occlusion  the  stress  upon  any  individual  tooth  is  lessened 
or  modified  by  the  occlusion  of  the  other  teeth  of  a  denture,  so  that  the 
conditions  of  any  tooth  as  part  of  a  denture  are  not  those  of  the  same 
tooth  standing  alone.  For  example,  the  incisors  normally  receive  a 
stress  which  ceases  as  soon  as  the  molars  and  bicuspids  are  in  perfect 
contact ;  in  the  absence  of  these  latter  teeth  the  entire  force  of  occlusion 
falls  upon  the  incisors,  and  they  are  unduly  strained. 

The  incisors  receiving  stress  in  a  direction  tending  to  their  outward 
displacement,  the  indication  in  crowning  is  to  provide  a  fixture  which 
shall  best  resist  this  direction  of  stress.  Evidently,  the  device  would  be 
a  rigid  rod  extending  through  the  longitudinal  axis  of  the  root ;  hence, 
post  crowns  are  selected  for  incisors. 

The  condition  of  the  root,  as  discussed  later,  may  demand  modification 
of  the  variety  of  post  croAvn  applied.  The  same  considerations  apply  to 
the  crowning  of  the  cuspidati.  With  the  bicuspids,  as  the  great  stress 
is  vertical,  firm  support  by  the  root  face  is  the  first  consideration  and,  as 
the  lateral  stresses  are  considerable,  auxiliary  support  may  be  derived 
through  posts.  The  lateral  stress  upon  a  first  bicuspid  being  greater 
than  upon  the  second,  owing  to  its  greater  over-bite,  a  bifurcated  pin 
furnishes  the  increased  support  required. 

The  same  ends  are  gained  in  the  bicuspids  by  the  use  of  barrel 
crowns ;  the  cement  underlying  them  forms  a  perfect  contact  with  the 
face  of  the  root,  thus  affording  the  full  measure  of  resistance  to  the  ver- 
tical stress  ;  the  collar  embracing  the  periphery  of  the  root  protects  it 
from  lateral  displacing  forces. 

With  the  molars,  the  greatest  stress  being  vertical,  support  is  de- 
manded from  the  entire  root  area  underlying  the  crown.  The  latter 
represents  primarily  a  block  resting  firmly  upon  a  broad  base.  The 
lateral  stress  is  guarded  against  by  having  one  or  two  posts  in  the  axes 
of  the  roots  or  by  the  periphery  of  the  crown  grasping  that  of  the  root- 
walls. 

It  is  evident  that  the  crown  best  adapted  to  meet  these  stresses  is 
that  having  a  barrel  form,  grasping  firmly  the  periphery  of  the  root ;  the 
retaining  cement  becomes  mechanically  part  of  the  tooth,  so  that  these 
crowns  rest  uniformly  upon  the  entire  area  of  the  root-face. 

Pin  crowns  of  the  variety  placed  upon  bicuspid  roots  are  occasionally 


PHYSIOLOGICAL  RELATIONS.  591 

employed  upon  molar  stumps,  but,  as  a  rule,  their  intrinsic  resistance  is 
not  as  great  as  that  offered  by  barrel  crowns. 

Although  by  their  position  and  form  molars  receive  less  lateral  stress 
than  bicuspids,  the  stress  transmitted  to  any  one  root  has  greater  effect 
than  with  the  bicuspids,  as  the  line  of  stress  in  a  ^      „^o 

molar  operates  at  a  greater  distance  from  the  line  of 
resistance  than  it  does  in  a  bicuspid,  and  the  leverage 
represented  is  correspondingly  increased  (Fig.  723). 
As  on  the  natural  crowns  of  molars  the  lateral  stress 
is  less  than  the  vertical,  artificial  crowns  placed  upon 
their  roots  should  be  formed  so  that  this  is  not  in- 
creased by  their  presence. 

Dr.  Bonwill  has  shown  the  anatomical  necessity 
that  the  cusps  of  any  tooth  be  not  longer  than  those 
of  the  teeth  anterior  to  it.^ 

When  it  is  desired  to  lessen  the  lateral  stress  upon  molar  stumps  the 
end  is  accomplished  by  a  shortening  of  the  cusps  of  the  crown. 

The  Forms  of  the  Teeth. 

The  great  consideration  as  a  governing  factor  in  the  placing  of  arti- 
iicial  crowns  is  the  forms  of  the  teeth.  This  includes  the  shapes  and 
sizes  of  the  roots  to  be  crowned  as  factors  determining  the  type  or 
variety  of  crown  selected. 

How  does  the  area  of  root-section  compare  with  the  length  of  the  root  ? 
and,  again.  How  do  these  factors  compare  with  the  length  and  breadth 
of  the  occlusal  surface  of  the  artificial  crown  ?  For  example,  two  roots 
may  have  the  same  length  and  the  same  sectional  area  :  one  requires  a 
crown  half  again  as  long  as  the  other  (Fig.  724),  or  the 
stress  of  occlusion  may  be  more  severe ;  obviously,  the  Fig.  724. 
mechanical  stress  upon  the  root  is  increased  in  the  ratio  of 
the  extent  of  its  occlusion  or  the  amount  of  increased  lever- 
age represented  in  the  crown  of  greater  length.  Or,  again, 
two  roots  having  the  same  length,  and  artificial  crowns  of 
the  same  length  and  breadth,  but  the  sectional  area  of  the 
face  of  one  root  greater  than  that  of  the  other,  it  is  evident 
that  the  resistance  afforded  by  the  root  of  smaller  section 
will  be  correspondingly  decreased.  A  long  heavy  root  will  bear  safely  a 
crown  which  if  set  upon  a  short  and  narrow  root  and  subjected  to  an 
equal  stress  would  result  in  the  loss  of  the  root. 

Physiological  Relations. 

Under  this  heading  are  considered  the  vital  conditions  of  the  tissues 
of  the  teeth  or  roots  and  of  their  sources  of  nutrition  and  support ;  if 
the  pulp  be  alive,  what  its  condition ;  and  whether  it  is  possible  or 
advisable  to  place  an  artificial  crown  without  effecting  the  destruction 
of  that  organ.  Teeth  are  occasionally  broken  in  such  a  manner  as  to 
render  restoration  of  form  by  filling  material  inadvisable,  and  yet  not 
uncovering  the  pulp,  the  latter  being  healthy  and  the  dentine  normal. 

^  Proceedings  of  Columbian  Dental  Congress. 


592  ARTIFICIAL  CROWNS. 

It  is  possible  in  some  of  these  cases  to  adjust  an  artificial  crown  without 
destroying  or  disturbing  the  pulp  :  it  is  evident  that  modifications  of  the 
barrel  crown  are  alone  applicable. 

Next,  what  is  the  texture  of  the  dentine  ?  Highly  organized  dentine 
will  bear  safely  a  strain  which  would  inj  ure  dentine  of  poorer  type.  The 
latter  type  of  tissue  is  non-resistant  to  the  progress  of  dental  caries,  and 
thus  needs  protection  against  contact  with  or  the  access  of  the  active 
causes  of  caries. 

The  condition  of  the  enamel  rarely  is  a  factor  in  the  plans,  except 
that  faulty  enamel,  through  its  liability  to  fracture  or  crumbling,  will 
sooner  or  later  leave  part  of  a  natural  crown  or  a  stump  for  the  attention 
of  the  prosthetist.  It  may  be  that  a  tooth  crown  consisting  in  large  part 
of  thin  and  discolored  enamel  is  removed  for  aesthetic  considerations  and 
replaced  by  an  artificial  crown. 

The  Condition  of  the  Pericementum. — This  includes  a  consideration 
of  the  existing  vital  relations  of  this  tissue,  and  the  possible  sources  of 
irritation  to  it  formed  by  the  placing  of  an  artificial  crown,  or  acting 
after  the  crown  is  set. 

Pathological  Relations. 

As  teeth  which  require  artificial  crowns  have  been  brought  to  their 
condition  by  the  action  of  pathogenic  agencies,  these  if  unchecked  will 
ultimately  cause  the  loss  of  the  root  itself:  they  are  therefore  the  most 
important  of  the  factors  requiring  attention. 

The  question  of  existing  pathological  conditions  and  their  treatment 
belongs  properly  to  the  province  of  dental  pathology  and  therapeutics ; 
but  the  present  subject  is  the  common  ground  upon  which  the  therapist 
and  prosthetist  meet :  their  offices  are  the  two  steps  of  a  common  opera- 
tion. 

If  a  tooth  contains  a  vital  pulp,  and  it  is  designed  to  retain  that 
organ,  the  infected  dentine,  that  invaded  by  the  carious  process,  should 
be  removed  with  the  same  care  as  though  it  were  being  prepared  for  the 
reception  of  a  filling.  Should  the  pulp  be,  or  have  been,  the  seat  of 
inflammation,  it  is  destroyed  and  removed.  If  it  is  to  remain  alive,  the 
same  care  is  observed  in  guarding  it  against  thermal  shock  as  with  fill- 
ings, so  that  after  placing  an  artificial  crown  upon  a  stump  containing  a 
vital  pulp  there  should  be  no  increased  response  to  applications  of  heat 
or  cold. 

When  post  crowns  are  indicated  the  pulp  is  to  be,  necessarily,  de- 
stroyed. 

The  extent  to  which  the  carious  process  has  invaded  the  dentine  is  a 
large  factor  for  consideration,  for  the  greater  the  loss  of  the  dentine  the 
weaker  the  root  becomes,  the  less  mechanical  resistance  it  affords,  so  that 
support  may  be  required  to  guard  the  weakened  structure  against  frac- 
ture. Again,  the  more  extensive  the  carious  process  the  greater  is  the 
probability  of  such  deep  infection  of  the  dentine  that  an  increased 
length  of  time  is  required  for  sterilizing  the  infected  tissue. 

The  present  condition  of  the  pericementum  and  its  past  history  are 
the  most  important  of  all  considerations.  It  is  possible  that  a  form  of 
crown  may  be  required  which  will  permit  of  ready  removal  in  case  of 


PREPARATION  OF  ROOTS;    THERAPEUTICS.  593 

recurring  pericementitis ;  however,  in  a  properly  treated  root  such  a 
contingency  should  be  a  remote  possibility. 

The  liability  or  disposition  of  the  pericementum  toward  inflammation 
may  enforce  a  lessening  of  the  stress  brought  to  bear  upon  it  through  the 
artificial  crown.  It  is  a  recognized  principle  of  surgery,  and  never  to  be 
lost  sight  of  in  crown-  and  bridge-work,  that  a  part  once  inflamed  has  an 
increased  tendency  toward  subsequent  inflammation. 

It  is  an  inflexible  rule  that  before  the  setting  of  an  artificial  crown 
the  root  bearing  it  must  have  such  preliminary  treatment  that  its  pulp- 
canal  and  substance  of  its  denture  are  rendered  aseptic,  and  if  possible 
antiseptic,  and  the  pericementum  must  be  brought  to  a  condition  of  health. 

Unless  the  root  be  firmly  fixed  and  supported  by  sound  alveolar 
structures  the  following  operations  prove  abortive  just  in  the  degree  that 
the  root  is  the  subject  of  anatomical  or  physiological  perversion.  It  must 
be  remembered  that  the  setting  of  an  artificial  crown  places  beyond  access 
the  most  important  means  of  combating  disease  of  the  crowned  root,  so 
that  the  assurance  of  continued  root-health  is  a  necessary  preliminary. 

Preparation  of  Roots;  Therapeutics. 

Under  this  heading  are  included,  first,  the  therapeutic  measures 
necessary  to  secure  the  continued  health  of  all  of  the  dental  tissues  and 
their  supports ;  and  next  the  mechanical  preparation  necessary  to  form 
the  root  into  a  resistant  base  to  which  a  crown  may  be  fitted  with 
exactitude. 

If  the  tooth  contain  a  live  pulp  which  has  been  the  seat  of  morbid 
action  ranging  from  congestion  to  suppuration,  it  is  to  be  destroyed  and 
thoroughly  removed.  In  single-rooted  teeth  this  destruction  may  occa- 
sionally be  effected  by  the  driving  process.  A  piece  of  orange-wood  is 
made  into  a  long  sharp  point ;  the  pulp  is  exposed  so  that  there  is  direct 
and  perfect  access  to  it :  if  it  be  hypersesthetic,  a  crystal  of  cocaine  is 
placed  upon  it  and  permitted  to  remain  for  five  minutes,  when  the 
pointed  stick  is  insinuated  between  the  pulp  and  its  walls  and  driven 
into  the  root  by  a  quick  blow  of  a  plugging  mallet.  The  stick  is  then 
withdrawn,  and  usually  the  pulp  is  found  clinging  to  it.  In  other  teeth, 
those  in  wdiich  such  direct  access  to  the  pulp-canal  cannot  be  had,  the 
nozzle  of  a  hypodermic  point,  attached  to  a  syringe  containing  a  solution 
of  cocaine  of  from  4  to  10  per  cent.,  is  inserted  beside  the  pulp  and  a 
drop  of  the  solution  forced  out ;  in  a  few  seconds  the  point  of  the 
syringe  is  thrust  quickly  into  the  substance  of  the  pulp,  and  the  injec- 
tion made.^  The  pulp  is  then  removed  by  means  of  broaches.  If  the 
necessary  apparatus  be  available,  the  pulp  may  be  placed  under  cocaine 
anaesthesia  through  the  agency  of  a  cataphoretic  current.  The  usual 
practice  is  to  destroy  the  pulps  by  means  of  a  paste  of  arsenic : 

I^.  Acid,  arsenosi, 

Cocain.  muriat.,  da.  gr.  j  ; 

Ol.  caryophyll.,  q.  s. 

M.  et  ft.  paste. 

8ig.  A  minute  portion  of  the  paste  placed  on  a  small  pledget  of 
cotton  is  laid  over  the  point  of  exposure. 

1  Dr.  Masfield,  Proc.  N.  J.  State  Le.nt.  Soc,  1894. 
38 


694  ARTIFICIAL  CROWNS. 

This  preparation  is  sealed  in  the  tooth  preferably  by  zinc  phosphate 
mixed  thin,  and  before  it  is  hardened  the  access  of  the  fluids  of  the 
mouth  to  its  surface  is  permitted. 

The  pain  following  arsenical  applications  to  the  pulp  is  caused  in 
great  part  by  the  pressure  of  the  retaining  filling  material.  Zinc  phos- 
phate flowed  in  the  cavity  causes  no  pressure,  and  its  Avetting,  before 
hardening  occurs,  renders  it  easy  of  removal.  In  from  twenty-four  to 
forty-eight  hours  the  pulp  is  then  removed  by  means  of  broaches. 

If  the  pulp  be  the  seat  of  purulent  inflammation  or  of  moist  gan- 
grene, it  should  be  removed,  so  that  none  of  the  pathogenic  organisms 
may  be  forced  into  the  tissues  about  the  apex.  The  root  and  the  de- 
generated pulp-tissue  are  filled  with  a  strong  penetrating  antiseptic, 
such  as  meditrina  (a  solution  of  hypochlorites),  and  this  is  permitted 
to  exercise  its  properties  before  the  broach  is  applied.  It  is  a  wise  pre- 
caution to  wash  the  mouth  well  with  this  solution  prior  to  opening  any 
pulp-chamber  in  which  there  is  putrescible  material.  When  possible,  the 
rubber  dam  is  applied,  the  cavity  dried,  and  a  strong  solution  of  sodium 
peroxide  carried  into  the  canal,  gently  stirring  it  with  an  iridio-platinum 
broach  :  as  soon  as  eifervescence  ceases  wash  out  the  canal  with  sterilized 
water,  and  repeat  the  applications  of  the  peroxide  until  access  is  had  to 
the  apex  of  the  root. 

The  dentine  of  roots  which  have  contained  gangrenous  pulps  is  the 
seat  of  more  or  less  albuminous  decomposition,  so  that  ample  time  should 
be  taken  in  sterilizing  it,  preferably  by  the  sodium  peroxide,  as  this  sub- 
stance is  itself  decomposed  into  sodium  hydrate  and  free  oxygen  :  the 
former  saponifies  the  fatty  products  of  decomposition  and  dissolves  the 
protoplasmic  filaments ;  the  oxygen  drives  out  the  dissolved  materials, 
and  eflPectually  destroys  any  organisms  present. 

If  there  be  no  exudation  from  the  apical  tissues  into  the  canal,  it 
is  the  common  practice  to  dry  out  the  canal  by  means  of  alcohol  and 
hot  blast,  and  fill  the  apical  portion  of  the  canal  with  a  gutta-percha 
cone  which  has  been  covered  by  an  antiseptic  oil — cajuput,  cinnamon,  or 
cassia. 

Should  the  apex  of  the  root  be  the  seat  of  an  abscess,  this  is  to  be 
cured  before  the  apical  foramen  is  sealed.  The  canal  is  washed  out  with 
the  sodium  peroxide  and  cleansed  thoroughly  :  no  harm  is  done  if  the 
solution  be  forced  through  the  root.  Succeeding  this,  a  solution  of  caustic 
pyrozone  is  pumped  through  the  canal  into  the  abscess-sac  until  the  pus 
is  driven  through  the  fistula.  As  a  rule,  these  roots  may  be  filled  at  once, 
and  the  abscess-sac  is  soon  obliterated  by  the  formation  of  new  tissue 
about  the  apex  of  the  root.  It  occasionally  happens  that  the  fistula  does 
not  close  after  one  injection,  so  that  as  a  precautionary  measure  the  per- 
manent hermetical  sealing  of  the  apex  of  the  canal  is  deferred  until  it  is 
seen  the  fistula  heals  and  the  normal  color  of  the  gum  over  the  aifected 
tooth  is  restored. 

Cases  present  at  times  which  give  a  history  of  a  fistula  alternately 
healing,  then  opening.  Even  after  repeated  injections  the-fistula  will  open 
periodically,  and  a  discharge  of  pus  or  serum  occur.  A  condition  is  present 
at  the  apex  of  the  root  which  demands  removal  by  amputation  of  the  apex. 
Before  the  pus  formed  at  the  apex  of  a  root  makes  its  escape  through 
a  fistulous  opening  in  the  gums  the  destruction  of  tissues  incidental  to 


PBEPABATION  OF  ROOTS;    THERAPEUTICS. 


595 


Fig.  725. 


or  characteristic  of  abscess  proceeds  in  all  directions,  so  that  by  the  time 
a  fistula  is  established  the  end  of  the  root  is  extending  into  an  irregular 
cavity,  the  pericementum  destroyed  for  some  distance  above  the  apex, 
and  the  uncovered  portion  of  the 
cementum  saturated  with  noxious 
material. 

When  the  pus  above  the  dotted 
line  (Fig.  725)  discharges,  the  fis- 
tula may  heal,  and  remain  closed 
until  an  increased  pus-formation 
again  re-establishes  the  fistula. 

The  gum  is  to  be  divided  above 
the  apex  of  the  root,  the  perice- 
mentum is  scraped  from  a  small 
area,  and  free  entrance  is  gained 
to  the  abscess-cavity  by  means  of 
sterilized  burs.      As  soon  as  the 

bleeding  is  checked  a  fissure  bur  is  passed  through  the  opening  and  the 
denuded  portion  of  the  root  cut  off  and  rounded.  The  sterilization  of 
the  canal  and  its  filling  have  preceded  the  amputation. 

In  what  are  known  as  blind  abscesses,  those  without  a  fistulous  tract 
leading  from  them  and  discharging  externally,  it  is  advisable  where 
possible  to  make  an  artificial  fistula.  The  mouth  is  sterilized  and  a 
crystal  of  cocaine  placed  on  the  gum  over  the  apex  of  the  root.  The 
length  of  the  root  is  measured  by  a  broach  in  the  canal,  and  this  length 
measured  on  the  gum  over  the  root.  A  crucial  incision  is  made  through 
the  gum,  the  bone  denuded  of  periosteum  over  a  small  area,  and  a 
spear-pointed  engine  drill  is  quickly  passed  through  the  bone  and  into 
the  abscess-cavity.  The  case  is  treated  then  as  a  simple  abscess.  The 
operation  may  be  made  almost  painless  by  injecting  a  few  minims  of  a 
4  per  cent,  solution  of  cocaine.  The  canal  is  filled  after  a  thorough 
sterilization,  and  pending  the  healing  of  the  abscess-cavity  the  external 
opening  is  kept  patulous  by  means  of  a  couple  of  strands  of  floss  silk 
acting  as  a  tent  and  means  of  drainage. 

Persistent  endeavor  should  be  made  to  enter  freely  and  cleanse  out 
perfectly  to  the  apex  all  the  fragments  of  pulp-tissue  in  the  roots  of 
teeth,  even  in  the  most  minute  canals.  The  introduction  of  the  use  of 
sulphuric  acid,  in  connection  with  broaches,  for  gaining  entrance  to, 
enlarging,  and  cleansing  canals,  by  Dr.  J.  E,.  Callahan,^  has  added  to  the 
operations  of  dentistry  a  most  valuable  expedient,  and  furnishes  a  means 
for  the  removal  of  a  common  cause  of  apical  pericementitis,  imperfect 
removal  of  pulp-fragments.  A  drop  of  a  50  per  cent,  solution  of  sul- 
phuric acid  is  placed  over  the  mouth  of  a  fine  canal,  and  pumped  into  it 
by  means  of  a  fine  Donaldson  broach. 

Much  patience  will  be  required  to  effect  the  desired  end  in  some 
teeth,  but  so  long  as  there  is  an  imperfectly  cleansed  canal  there  is  the 
ever-present  fear  of  the  possibility  of  abscess,  and  if  the  crown  be  prop- 
erly set,  it  is  most  difficult  to  cure  the  diseased  condition. 

Roots  or  teeth  which  have  a  portion  of  their  surface  overgroAvn  by 
a  hypertrophied  gum-tissue  must  have  the  latter  removed,  so  that  the 

^  Dental  Cosmos,  vol.  xxxvi.  p.  329. 


596 


ARTIFICIAL   CROWNS. 


field  of  operation  may  be  open.  If  it  be  a  pendulous  mass,  the  gum  is 
excised  sufficiently  to  free  the  root  outline.  If  the  margins  of  the  root 
be  covered  by  the  gum,  it  is  to  be  pressed  back  until  the  field  of  opera- 
tion is  free.  The  canal  and  the  pockets  beneath  the  gum  margins  are 
washed  out  with  meditrina  and  the  canal  and  face  of  the  root  dried.  A 
block  of  temporary  stopping  is  made  and  formed  into  a  truncated  cone,, 
the  small  end  of  which  is  pressed  against  the  face  of  the  root,  and  the 
mass  is  flattened  so  that  it  presses  the  gum  away  from  the  root  on  all 
sides.  "  Should  there  not  be  sufficient  concavity  in  the  root  to  hold  the 
stopping,  a  large-headed  carpet  tack  may  be  pressed  into  the  canal  and 
the  gutta-percha  wedge  built  around  the  post."  ^ 


Mechanical  Preparation  of  the  Root. 

The  manipulations  included  in  the  mechanical  preparation  of  teeth  or 
roots  for  the  reception  of  artificial  crowns  are  of  two  varieties  :  first,  the 
reduction  of  the  existing  volume  to  the  necessary  form  and  dimensions  ; 
second,  those  cases  in  which  it  is  necessary  to  restore  in  part  the  form  of 
the  root  lost  by  decay,  so  that  it  will  serve  as  a  base  for  a  crown. 

Fig.  726. 


Fig.  728. 


Crowns  supported  by  posts  should  be  so  adapted  to  the  roots  upon 
which  they  are  placed  that  their  peripheral  junction  is  as  nearly  perfect 


Fig.   729. 


Herbst's  rotary  flies. 


as  possible  ;    there  should    be  nothing    between  their  surfaces  but    an 
attenuated    layer  of  the  retaining  medium.     At    no  point    should  the 


^  Win.  H.  Trueman. 


MECHANICAL   PREPARATION  OF  THE  ROOT 


597 


surfaces  overlap ;  an  instrument  passed  around  the  line  of  union  should 

discover  no  projection  of  the  crown  beyond  the  root. 

Roots  should  be  so  prepared  that  they  furnish  adequate  mechanical 

support  to  their  artificial  crowns.  As  they  represent  also  restoration  of 
form,  their  bases  should  be  so  shaped  as  to  permit  the 
Fig.  730.  accurate  adaptation  of  anatomically  correct  substitutes. 
The  first  class  of  root-  or  tooth-shaping  operations 
are  found  in  those  cases  where  it  is  necessary  to  reduce 
an  entire  crown  or  a  considerable  portion  of  one  to 
desired  dimensions. 

When  decrowning  is  necessary  to  fit  teeth  contain- 
ing vital  pulps  for  service  as  the  bases  of  abutment 
crowns  of  dental  bridges,  they  may  be  removed  after 
the  following  manner :  The  edge  of  a  diamond  or 
sharp  corundum  disk  is  applied  to  the  outer  and  inner 
walls  of  the  tooth  until  it  is  deeply  grooved  (Fig.  726) ; 
the  edges  of  a  pair  of  excising  forceps  are  then  placed 
in  the  grooves,  and  by  a  sudden  pressure  the  crown  is 
broken  off,  leaving  the  pulp  protruding.  This  organ  is 
then  destroyed  by  the  driving-out  process  or  extirpated 
after  cocaine  injection.  This  method,  if  practised  upon 
teeth  containing  dead  pulps,  is  occasionally  followed 
by  obstinate  pericemental  disturbance. 

The  crowns  of  pulpless  teeth  may  be  readily  re- 
moved by  making  with  a  spear-pointed  drill  a  series 
of  perforations  from  the  outer  to  the  palatal  surface  of 
the  tooth  ;  these  should  all  be  in  one  line,  about  one- 
sixteenth  of  an  inch  above  the  gum  margin  (Fig.  727). 
A  dentate  fissure  bur  (Fig.  728)  is  passed  through  the 
middle  opening,  and  by  cutting  laterally  the  crown  is 
soon  removed.     Irregular  fragments  of  crowns  may  be 


\ 
J 


I  i 


Fig.  731. 


o  o  O 

Pivoting. 


Facers. 


Root-facers. 


chipped  away  piecemeal  by  means  of  a  small  pair  of  excising  forceps 
until  they  are  almost  on  a  line  with  the  gum  margin.  The  shaping 
of  the  root  face  may  be  accomplished  by  means  of  oval  files  made 
for  that  purpose  (Fig.  730).    Stump  corundums  are  eifective  instruments 


598  ARTIFICIAL  CROWNS. 

for  the  same  purpose,  but  better  than  either  are  the  rotary  files  of 
Herbst  (Fig.  729),  which  shape  the  root  face  as  it  should  be,  its  edge 
parallel  with  the  gum  margin. 

The  trimming  is  continued  until  the  root  face  is  at  uniform  depth 
of  about  one-twentieth  of  an  inch  beneath  the  gum  line.  At  its  labial 
aspect  the  cutting  should  be  slightly  deeper,  so  that  the  line  of  junction 
of  crown  and  root  may  be  effectually  concealed. 

A  safe  and  rapid  method  of  reducing  the  faces  of  roots  or  of  cutting 
down  broken  teeth  is  by  means  of  Ottolengui's  root-facers.  Their  action 
and  application  are  illustrated  in  the  cut  (Fig.  731). 

Reducing  Teeth  for  Barrel  Crowns. 

It  is  essential  that  the  edges  of  all  barrel  or  collar  crowns  shall  form 
a  perfect  joint  with  the  periphery  of  the  root.  This  portion  of  the 
root  should  have  a  greater  sectional  area  than  any  portion  of  the  tooth 
over  which  the  barrel  is  passed  in  adjusting  it.  The  walls  of  the  root 
and  tooth  should  therefore  be  at  least  parallel  above  the  crown  edge  line, 
and  it  is  better  if  they  be  given  a  slight  slope,  so  that  in  placing  the  bar- 
rel it  is  being  thrust  over  the  frustum  of  a  rounded  pyramid  (Fig.  732), 
It  will  be  noted  in  the  appended  figures  that  the  periphery  of  the  roots 
of  the  teeth  are  usually  larger  at  the  gum  margin  than  at  a  point  one- 
sixteenth  of  an  inch  beneath  this  margin ;  moreover,  the  form  changes, 
so  that  a  tooth  or  root  must  be  so  formed  that  the  portion  of  the  crown 
or  root  extending  beyond  the  gum  has  a  less  circumference  than  the 
portion  one-sixteenth  of  an  inch  beyond  the  given  margin. 

The  evils  attending  and  following  the  placing  of  this  class  of  crowns 
are  due  in  great  part  to  inaccurate  adaptation  of  the  edge  of  the  collar 
to  the  periphery  of  the  root.  It  is  a  task  of  some  little  difficulty  to 
properly  shape  a  root  for  the  reception  of  a  collar  crown,  and  no  easy 
operation  to  accurately  fit  a  metallic  band  to  the  prepared  root. 

It  is  a  common  observation  that  very  many,  perhaps  a  great  majority, 
of  these  crowns  are  imperfectly  fitted  or  the  root  improperly  prepared. 
An  instrument  passed  around  their  borders  discovers  the  existence  of  an 
irregular  shoulder  produced  by  the  lack  of  adaptation  of  the  barrel  edge 
(Fig.  733,  a).  Such  spaces  form  pockets  in  which  food  deposits  and  secre- 
tions find  lodgement,  so  that  the  irritation  produced  by  the  projecting 
collar  edge  is  increased  by  contact  with  the  products  of  fermentative 
decomposition  of  the  deposits,  and  localized  gingivitis  and  pericemen- 
titis are  liable  to  occur. 

The  sectional  area  at  the  gum  line  is  greater  than  beneath  it,  so  that 
a  barrel  fitted  to  a  root  cut  off  at  the  gum  margin  would  necessarily 
leave  projecting  edges  if  forced  above  that  line.  The  line  of  crown  and 
root  adaptation  should  be  as  shown  in  Fig.  734. 

In  cutting  down  large  tooth  remnants,  such  as  molars,  to  the  slightly 
tapering  form  required,  a  large  revolving  disk  of  corundum  or  a  diamond 
disk  (see  Fig.  726)  is  held  against  the  four  walls,  and  its  edge  carried 
slightly  beneath  the  gum  margin  until  the  tooth  represents  a  truncated 
pyramid  :  the  disk  is  carried  over  all  accessible  portions  of  the  walls. 
The  corners  of  the  teeth  or  some  of  them  are  usually  inaccessible  to 
the  disk,  so  that  they  are  to  be  shaped  by  means  of  smaller  implements, 


BEDUOINQ   TEETH  FOB  BABBEL   CBOWNS. 


599 


small  corundum  points,  tapering  burs.     An  effective  instrument  for  this 
purpose  is  found  in  Dr.  C.  S.  Case's  enamel-cleaver  (Fig.  735). 


A  crown  or  tooth  remnant   entirely  freed  of  its   enamel  has  the 
correct  form  for  the  proper  adjustment  of  barrels  or  collars,  so   that 


600 


ARTIFICIAL   CROWNS. 


in   broken-down  teeth  tlieir  walls  may  be  shaped  by  the  removal  of 
the  enamel  through  the  aid  of  these  instruments. 

The  instrument  of  Dr.  W.  S.  How  (Fig.  736)  and  those  of  Dr.  R.  W. 
Fig.  733.  Fig.  735. 


Starr  (Fig.  737)  are  used  to  give  the 
proper  form  to  roots  for  the  reception 
of  collars. 

Fig.  734. 


Crowns  which  depend  for  retention 
upon  a  barrel  are  to  have  as  much  of  the 
tooth  stump  left  as  possible  compatible 
with  perfect  adaptation  of  the  crown^ 
and,  if  for  anterior  teeth,  with  the  non- 
exposure  of  the  gold. 

Restoring  Root  Forms. 

It  is  necessary  that  the  root  of  a  tooth 
should  possess  sufficient  strength  and  such 
form  as  to  furnish  a  firm  support  to  the 
artificial  crown. 

Occasionally  cases  present  in  which 
there  has  been  such  extensive  loss  of 
tooth-substance  that  hypertrophied  gum 
is  found  overhanging  the  edges  of  a  root 
which  has  been  extensively  invaded  by 
the  progress  of  caries.  In  such  cases  the 
root  form  is  to  be  restored  sufficiently  to  furnish  a  good  base.  After  the 
free  application  of  powerful  but  unirritating  antiseptics  to  the  recesses 
of  the  gum  and  the  cavity  of  the  root,  masses  of  temporary  stopping  are 
employed  as  described  to  free  the  interior  of  the  root  and  its  face  from 
the  overlying  gum.  The  root  is  thoroughly  sterilized,  its  pericementum 
brought  to  a  condition  of  assured  health,  and  the  apex  of  the  canal  sealed. 


RESTORING  ROOT  FORMS. 


601 


It  is  now  required  to  restore  the  root  form  by  means  of  some  rigid 
and  insoluble  material.  All  things  considered,  a  good  amalgam  is  the 
material  best  adapted  for  this  purpose.  If  the  root  is  that  of  a  bicuspid 
or  a  molar,  one  on  which  a  collar  crown  is  to  be  placed,  the  filling  mass 
is  built  down  so  that  the  collar  encloses  it,  finding  its  support  in  the 
filling,  and,  if  possible,  through  some  grasp  upon  the  root  also. 

The  first  step  is  fitting  a  matrix  to  the  root  in  whi(!h  the  amalgam  is 
to  be  packed.  A  small  cylinder  of  moldine  is  packed  over  the  root  face, 
its  external  portion  being  left  as  a  bulbous  protrusion.  While  the  mol- 
dine is  in  position  a  small  impression-tray  filled  with  the  same  material 
is  used  to  secure  and  withdraw  the  mass  covering  the  root  face.  Into 
this  impression  a  fusible-metal  cast  is  run,  on  which  is  adjusted  a  tube  of 
German  silver  or  copper,  fitting  the  root  accurately  and  being  deep 
enough  to  grasp  the  periphery  of  the  root  firmly  and  to  extend  one- 
eighth  of  an  inch  or  more  above  the  edge  of  the  gum.  This  tube  is  placed 
in  position — the  rubber  dam  adjusted  over  it  and  the  adjoining  teeth. 

The  root  is  next  dried  well  and  filled  with  a  strong  antiseptic.     The 
canal  is  cleaned  and  tapped  for  the  reception  of  a  metal  screw ;    after 
placing  a  small  piece  of  soft  phosphate  of 
zinc  on  its  extremity  it  is  screwed  into  place  Fig.  738. 

(Fig.  738). 

The  root  is  given  an  undercut  and  groov- 
ed to  aid  in  retaining  the  amalgam.  Amal- 
gam is  packed  about  the  pin,  over  the  root 
face,  until  the  tube  is  filled  to  dotted  lines 
(Fig.  738) ;  this  is  done  by  using  a  ball  of 
bibulous  paper,  which  is  held  in  a  pair  of 
pliers  and  applied  to  press  out  all  surplus 
mercury,  which  is  then  removed,  and  the  fill- 
ing completed  with  amalgam  from  which  the  surplus  mercury  has  been 
wrung  by  means  of  heavy  pliers.  When  the  tube  is  full,  use  sponge 
gold  to  rub  into  the  amalgam  and  absorb  any  free  mercury.  The  filling 
should  be  hard  before  removing  the  rubber  dam.  An  alloy  containing 
at  least  55  per  cent,  of  silver  and  5  per  cent,  of  copper  should  be  used. 

After  twenty-four  hours  the  tube  should  be  split  by  cutting  through 
it  with  a  hatchet  excavator,  the  ends  bent  back  and  removed. 

At  the  external  (labial  or  buccal)  edge  the  amalgam  should  be  ground 
down  to  a  level  with  the  border  of  the  gum. 

If  desired  the  tube  may  be  made  of  thin         Fig.  739.  Fig.  740. 

platinum,  which  is  to  remain,  covering  the 


amalgam  mass.  For  anterior  teeth,  when 
a  pin  support  is  required  in  addition  to 
the  collar,  special  provision  must  be  made 
for  it.  After  placing  the  cylinder  over  the 
root  and  adjusting  the  rubber  dam,  a  plat- 
inum tube  is  made  of  thin  plate  and  of  a 
diameter  to  receive  a  No.  17  wire.  This 
is  to  be  anchored  for  the  reception  of  a  post  of  that  size.  The  wire, 
one-eighth  of  an  inch  longer  than  the  tube,  is  touched  with  vaseline  and 
inserted  in  the  tube,  a  small  pellet  of  zinc  phosphate  is  placed  in  the 
canal,  and  the  tube  and  wire  pushed  into  position.     This  tube  and  walls 


Correct  cervical 
outline. 


Faulty  outline. 


602  ARTIFICIAL   CROWNS. 

of  the  cylinder  encircling  the  root  must  be  parallel,  or  the  finished  crown 
cannot  be  placed  properly.  Undercuts  are  made  and  amalgam  packed 
as  described  before.  When  the  amalgam  has  set  the  wire  may  be  with- 
drawn from  the  inner  tube,  having  been  greased  lightly  ;  the  zinc  phos- 
phate does  not  retain  the  distal  extremity.  If  the  outer  tube  is  of 
platinum,  it  may  remain  if  the  operator  desire. 

In  shaping  the  external  cervical  margins  or  edges  of  roots  care  must 
be  exercised  to  give  them  such  an  outline  that  the  artificial  crown  has  a 
cervical  edge  of  the  same  outline  as  that  of  the  adjoining  teeth.  Disre- 
gard of  this  precaution  produces  unsightly  results.  Particular  care  must 
be  taken  in  shaping  the  external  border  of  collar  crowns,  as  upon  this 
detail  depends  not  a  little  of  the  artistic  success  of  the  piece  (Figs.  739 
and  740). 

Requisites  of  a  Crown. 

Artificial  crowns  should,  as  nearly  as  possible,  restore  the  appearance 
and  function  of  the  natural  teeth.  Moreover,  by  their  presence  they 
should  afford  no  more  opportunity  for  tho  action  of  disease-producing 
agencies  than  when  a  natural  crown  is  upon  a  pulpless  root.  This  rule 
is  impossible  of  exact  fulfilment,  but  it  is  possible  that  by  a  correct 
artificial  crown,  properly  placed  upon  a  healthy  root,  the  possibilities  of 
disease  processes  arising  may  be  reduced  to  a  minimum,  and  by  an  im- 
properly made  or  placed  crown  the  probabilities  of  subsequent  disease 
are  increased. 

All  crowns  must  rest  firmly  upon  the  face  of  the  root  upon  which 
they  are  placed.  The  contact  must  be  at  all  points  of  the  edge  of  a 
crown  with  the  tooth  surface.  If  of  porcelain,  it  must  correspond  in 
shape,  size,  shade,  and  position  with  its  fellow,  and  must  subserve  the 
purposes  of  a  crown  in  mastication. 

There  should  be  at  no  part  any  projection  which  can  form  part  of  a 
pocket,  nor  any  point  which  can  act  as  an  irritant  to  vital  tissue.  The 
line  of  junction  between  tooth  and  crown  should  be  clean  and  clear,  so 
that  neither  the  surface  of  the  root  projects  beyond  the  edge  of  the  crown 
nor  the  edge  of  the  crown  beyond  that  of  the  root. 

If  a  barrel  or  collar  crown,  the  upper  edge  of  the  collar  or  barrel 
must  be  in  close  contact  with  the  root  surface.  It  should  extend  far 
enough  beneath  the  margin  of  the  gum  to  grasp  the  root  firmly,  but 
should  not  extend  to  the  alveolar  border.  A  limited  portion  of  perice- 
mentum is  destroyed  in  trimming  a  root,  and  the  collar  should  not 
extend  beyond  this  point :  as  the  collar  represents  or  replaces  the  upper 
border  of  enamel,  it  should  not  extend  much  beyond  the  depth  of  the 
enamel  line  unless  the  gum  should  have  receded  from  about  the  tooth. 

Porcelain  crowns  should  have  the  porcelain  protected  against  frac- 
ture, either  by  the  inherent  strength  of  all  porcelain  crowns  themselves, 
their  bulk  supplying  the  strength  required,  or,  if  a  porcelain  facing,  the 
facing  should  be  protected  by  a  metallic  backing  against  the  force  or 
shocks  of  mastication. 

For  posterior  teeth  the  details  as  to  correspondence  of  size  and  con- 
tour are  equally  important,  and  in  addition  their  articulating  surfaces 
•should  have  such  an  arrangement  of  cusps  and  sulci  that  the  normal 
masticating  surface  is  restored. 


PARTIAL   CROWNS.  603 


Type  Selected. 


As  a  general  rule,  no  root  anterior  to  the  second  bicuspids  should  be 
crowned  with  an  all-gold  crown.  None  of  the  incisors  or  cuspids  should 
show  any  but  a  porcelain  surface.  Healthy  roots  which  have  not  been 
invaded  by  caries,  if  of  good  size  and  structure,  as  a  rule,  may  be  fitly 
crowned  with  some  form  of  the  pin  crown. 

Logan  crowns  are  adapted  when  the  root  is  of  good  structure  and 
when  form  and  color  corresponding  exactly  to  the  adjoining  tooth  can  be 
had,  and  when  the  bite  is  not  too  close  to  cause  weakening  of  the  porce- 
lain by  the  necessary  grinding,  and  where  the  correct  cervical  surface 
outline  can  be  had. 

The  pin  and  plate  crown  is  adapted  for  use  on  sound  roots.  This 
variety  produces  a  greater  mechanical  strain  upon  a  root  than  does  the 
Logan,  as  the  force  received  by  it  is  directed  first  upon  the  anterior  wall 
of  the  pulp-canal ;  second,  upon  the  outer  surface  of  the  root.  With  the 
Logan  crown  the  force  received  is  transmitted  primarily  to  the  outer 
surface  of  the  root,  and  stress  is  exerted  secondarily  upon  the  walls  of 
the  pulj)-canals.  The  Logan  crown  can  therefore  be  used  upon  more 
frail  roots  than  the  pin  and  plate  variety,  as  the  stress  tending  to  fracture 
a  root  longitudinally  is  greater  with  the  latter. 

Partial  Crowns. 

Occasionally  cases  are  seen  where  the  loss  of  tooth-substance  is  not 
sufficient  to  demand  the  sacrifice  of  an  entire  crown  to  be  replaced  by 
one  of  the  artificial  crowns  described,  and  yet  is  so  extensive  or  in  such 
situations  that  restoration  by  means  of  filling  materials  is  impracticable : 
it  is  at  times  advisable  to  apply  one  of  the  devices  known  as  partial 
crowns. 

The  first  variety  of  such  cases  are  those  in  which  one  of  the  anterior 
teeth  has  been  fractured  transversely  at  about  the  middle,  without  expos- 
ing or  destroying  the  vitality  of  the  pulp. 

Usually  these  cases  have  the  contour  restored  by  means  of  heavy 
rolled  foil  at  the  hands  of  the  operator.  As  the  appearance  of  a  mass  of 
gold  in  so  conspicuous  a  place  may  be  objected  to  by  the  patient,  the  ope- 
rator is  compelled  to  resort  to  the  use  of  porcelain  to  effect  the  restoration. 

The  difficulties  of  this  substitution  are — securing  sufficient  support 
for  the  porcelain  tip  ;  accurately  matching  the  color  of 
the  natural  tooth  ;  disguising  the  line  of  juncture  of  Fig.  741. 

tip  and  tooth ;  and  lack  of  strength  in  a  porcelain     f ■  ^-<^^ 

piece  of  such  size.  'r'Til'        (^]Sm 

The  surface  of  the  broken  tooth  is  smoothed  and 
squared,  and  dressed  to  as  great  a  depth  as  pos- 
sible without  exposing  the  pulp.  Upon  this  pre- 
pared surface  a  piece  of  platinum  plate  No.  3-5  is 
burnished  to  close  adaptation  (Fig.  741). 

At  three  points  holes  are  drilled,  the  middle  one 
not  on  a  straight  line  with  the  others,  as  deep  as  may 
be  without  encroachment  upon  the  pulp  :  these  cavities  are  to  be  made 
while  the  platinum  plate  is  on  the  tooth  ;    in  each    of  the  openings  a- 
screw  is  placed,  fitting  the  cavities  easily.     Adhesive  wax  flowed  over 


604  ARTIFICIAL  CROWNS. 

the  projecting  ends  of  the  screws  attaches  screws  and  plate,  which  are 
removed  in  one  piece,  invested,  and  the  screws  nnited  to  the  plate  by 
means  of  24-carat  solder. 

The  piece  is  transferred  to  the  root,  the  exposed  ends  of  the  screw 
dressed  to  within  one  thirty-second  of  an  inch  of  the  plate,  and  the  plate 
burnished  to  perfect  adaptation  with  the  tooth  surface.  At  the  labial 
aspect  the  platinum  is  dressed  to  the  tooth  outline,  and  made  so  thin 
that  its  edge  is  almost  imperceptible. 

A  plaster  impression  of  the  parts  is  taken  in  which  the  small  plate  is 
withdrawn.  A  model  of  sand  and  plaster  is  poured  with  the  utmost  care, 
and  when  very  hard  the  impression  is  picked  away. 

A  cross-pin  tooth  having  the  pins  very  close  to  the  cutting  edge  is 
selected.  Its  color  should  match  as  nearly  as  may  be  that  of  the  tooth 
upon  which  it  is  to  rest.  It  is  better  to  have  the  tooth  a  trifle  more 
yellow  than  its  fellow,  as  the  presence  of  a  platinum  backing  gives  a 
bluish  tinge ;  if  the  tip  is  blue,  a  24-carat  gold  backing  produces  a 
yellowish  tint. 

The  porcelain  is  fitted  by  means  of  fine  corundum  wheels  until  the 
line  of  union  is  as  nearly  perfect  as  can  be  made.  It  is  backed  with 
platinum  No.  28  or  24-carat  gold  No.  27,  attached  to  the  plate  with 
adhesive  wax,  and  then  sand-and-plaster  investment  is  used  to  cover  the 
porcelain  and  retain  it  in  position. 

At  the  palatal  aspect  the  porcelain  is  dressed  out  to  expose  the  heads 
of  the  screws.  When  the  investment  has  set  the  adhesive  wax  is  removed, 
and  small  pieces  of  thin  platinum  plate  are  used  to  fill  the  little  space  be- 
tween the  base  of  the  porcelain  and  the  plate.  Solder  with  24-carat  gold  if 
the  plate  and  backing  are  of  platinum,  or  with  22-carat  solder  if  of  gold. 

Finish  and  set  with  zinc  phosphate,  permitting  the  cement  to  set 
half  an  hour  before  removing  the  rubber  dam. 

If  the  pulp  has  been  exposed,  it  is  destroyed  and  anchorage  secured 
in  the  canal  by  means  of  a  long  pin. 

Incisive  edges  may  be  made  of  gold  for  pulpless  teeth  after  the  fol- 
lowing method  :  The  labial  edge  of  the  tooth  is  filed  square.  A  piece 
of  thin  platinum.  No.  36,  is  pressed  into  accurate  apposition  with  the 
broken  edges  and  surface  of  the  tooth,  and  burnished  over  the  edges 
for  about  one-sixteenth  of  an  inch.  The  plate  is  perforated  over  the 
pulp-canal,  and  a  platinum  wire  of  No.  18  gauge  is  thrust  through  the 
perforation  :  the  platinum  film  grasping  it  tightly  on  all  sides,  it  is  with- 
drawn, bringing  the  plate  with  it.  The  pieces  are  united  by  means  of 
pure  gold  as  solder,  and  returned  to  the  tooth  and  burnished  into  perfect 
apposition.  A  bite  is  taken,  and  next  an  impression,  in  which  the  post 
and  plate  are  withdrawn.  A  model  and  articulating  model  are  made ; 
the  amount  of  restoration  required  is  noted.  A  stick  is  carved  to  repre- 
sent the  cutting  edge,  and  is  driven  into  an  asbestos  mat  deeper  than  the 
necessary  height  of  the  tip.  Pure  gold  is  melted  in  this  depression,  and 
while  molten  its  upper  surface  is  flattened  by  quickly  pressing  against  it 
a  smooth  piece  of  charcoal.  The  protruding  end  of  the  post  is  filed  down 
to  within  one  thirty-second  of  an  inch  of  the  plate.  The  gold  ingot  is 
filed  to  a  close  joint  with  the  labial  edge  of  the  plate :  its  inner  surface 
may  be  short  of  contact  to  perfectly  admit  solder. 

The  cutting  edge  is  filed  to  an  accurate  occlusion,  but  left  a  trifle 


PARTIAL  CROWNS.  605 

long  to  allow  for  loss  in  finishing.  The  surface  of  the  platinum  and  the 
base  of  the  tip  are  covered  by  borax.  If  the  model  has  been  made  of 
investing  material,  enough  of  it  is  placed  over  the  tip  to  hold  it  in  posi- 
tion. If  of  plaster,  an  opening  is  made  in  the  model  to  gain  access  to 
the  base  of  the  pins.  The  tip  is  cemented  to  the  plate  by  means  of  wax 
flux  ;  pressure  upon  the  end  of  the  post  pushes  the  fixture  from  the 
model.  It  is  invested  and  soldered  from  its  palatal  surface  with  22- 
carat  solder.  Its  surfaces  are  dressed  down  to  the  proper  contour,  the 
overlap  of  the  platinum  at  the  base  giving  the  base  outline,  to  which  the 
piece  is  to  be  tiled.     It  is  smooth,  polished,  and  set  with  zinc  phosphate. 

A  better  method  is  constructing  the  tip  entirely  of  porcelain ;  this 
may  be  accomplished  by  selecting  the  tip  of  a  porcelain  tooth,  adapting 
it  to  a  plate  as  described ;  the  attachment  of  the  two  is  made  by 
adding  fusible  porcelain  and  baking  in  a  furnace.  (See  also  methods  in 
Chapter  VI.) 

Shells  of  gold  having  the  appearance  externally  of  large  fillings  are 
occasionally  employed  in  restoring  the  contour  of  teeth.  The  method  is 
particularly  applicable  to  cases  requiring  a  large  phosphate  filling.  The 
gold  serves  as  an  outer  shell  which  by  its  smooth  surface  and  protection 
of  the  phosphate  from  the  action  of  the  fluids  of  the  mouth  preserves 
the  cement  from  disintegration  for  a  long  period.  A  satisfactory  method 
of  forming  these  pieces  is  as  follows :  The  tooth  is  excavated  as  for  a  phos- 
phate filling  ;  the  enamel  edges  are  made  smooth,  clear,  and  distinct,  then 
bevelled.  Should  the  cavity  occupy  only  the  masticating  surface  of  the 
tooth,  a  piece  of  softened  modelling  compound  is  placed  in  the  cavity 
and  the  patient  directed  to  close  the  bite.  A  piece  of  heavy  pattern  foil 
is  then  laid  over  the  compound  and  bitten  upon.  When  the  foil  is  re- 
moved the  compound  is  short  of  occlusion  about  the  thickness  of  No. 
30  plate.  The  cavity  edges  are  cut  clear  of  the  compound,  showing  their 
outlines  distinctly.  An  impression  is  taken  in  moldine  and  a  die  made. 
A  piece  of  pure  gold  of  No.  30  is  annealed,  swaged  on  this  die,  and  its 
edges  filed  to  fit  the  cavity  outlines  perfectly. 

Small  openings  are  drilled  through  the  cap  to  receive  the  ends  of 
wire  loops.     Pieces  of  No.  22  wire  about  one-quarter  of  an  inch  long 
are  bent  into  U  form  ;  four  of  them  are  required  to  hold  the 
cap  perfectly.    The  loops  have  their  ends  thrust  through  the    Fig.  742. 
openings,  a  minute  piece  of  No.  22-carat  solder  placed  beside 
each  exposed  end,  the  cap  laid  on  a  block  of  charcoal,  and  the 
solder  fused  by  a  fine  blowpipe  flame.     It  is  safer  to  cut  de- 
pressions in  the  die  corresponding  to  the  positions  of  the  loops, 
then  dress  down  the  ends  and  reswage  (Fig.  742). 

Should  the  cavities  include  the  approximal  walls,  the  tooth  form  is 
restored  by  means  of  zinc  phosphate  ;  the  cavity  edges,  which  have  been 
dressed,  are  scraped  free  from  the  cement.  Particular  care  is  required 
when  the  gold  extends  over  the  masticating  surface  that  the  phosphate 
be  cut  down  to  allow  for  the  lamina  of  gold.  An  impression  is  taken 
and  a  fusible  metal  die  made.  When  the  approximal  space  is  minute,  it 
will  be  necessary  to  pass  a  saw-blade  between  the  teeth  on  the  die  to 
represent  the  space.  A  piece  of  24-carat  plate  No.  30  is  swaged  and 
burnished  to  fit  the  outlines  on  the  die,  and  openings  made  for  two  loops 
— one  on  the  masticating,  the  other  on  the  approximal  wall. 


606  ARTIFICIAL   CROWNS. 

The  piece  is  transferred  to  the  natural  tooth  and  its  edges  burnished 
into  accurate  apposition  with  all  the  bevelled  enamel  edges.  Removed 
from  the  tooth,  the  wire  loops  are  placed  in  position  and  sol- 
dered. It  is  advisable  to  flow  solder  in  the  angle  to  stiffen  the 
piece.  (See  Fig.  743.)  The  rubber  dam  is  adjusted  and  the 
greater  portion  of  the  cement  is  cut  out.  A  mix  of  jjlastic 
phosphate  is  made ;  small  portions  are  packed  in  the  loops, 
and  next  the  cavity  itself  is  filled,  when  the  facing  is  pressed  into 
place.  The  piece  should  now  remain  undisturbed  for  at  least  fifteen 
minutes. 

In  cavities  involving  both  approximal  walls  and  the  masticating  sur- 
face the  piece  is  shaped  and  the  retaining  bar  placed  as  in  Fig.  744. 
Another  application  of  the  device  is  seen  in  Fig.  745. 

Fig.  744.  Fig.  745. 


Gold  blocks,  to  be  placed  in  lieu  of  gold  fillings  made  of  foil,  are 
constructed  after  the  following  method  :  The  cavity,  usually  in  an  incisor, 
is  to  have  its  edges  trimmed  and  squared.  A  piece  of  annealed  platinum 
No.  50  is  pressed  and  burnished  into  the  cavity  and  over  its  margins.  In 
the  platinum  form  adhesive  wax  is  placed  and  carved  to  the  proper  con- 
tour. It  is  chilled,  withdrawn  from  the  cavity,  and  invested  in  a  mix- 
ture of  pumice  and  plaster.  The  wax  is  burned  out,  and  in  the  matrix 
pure  gold  is  melted  under  a  fine  blowpipe  flame.  The  piece  is  trimmed 
:and  smoothed  to  correct  contour.  It  is  retained  in  the  tooth  by  means 
£)f  zinc  phosphate. 

The  Post  and  Plate  Crowns. 

These  are  crowns  which  have  posts  fitting  the  enlarged  pulp-canal  for 
support.  The  proper  size  and  shape  of  this  post  are  about  those  used  in 
the  familiar  Logan  crown. 

A  root  which  has  lost  no  substance,  or  no  more  of  the  periphery  of 
its  pulp-canal  than  will  receive  a  post  of  this  size,  is  usually  a  fit  root 
for  the  application  of  a  post  crown.  Should  there  be  a  loss  of  sub- 
stance in  excess  of  this  amount,  a  supporting  band  is  advisable. 

The  size  of  the  post  may  also  be  had  in  a  flattened  wire  of  14  B.  & 
S.  gauge  and  somewhat  tapered  toward  its  extremity.  The  flattening 
increases  the  resistance  in  the  long  diameter,  which  occupies  the  antero- 
posterior line  of  the  pulp-chamber,  the  line  of  greatest  strain.  Round 
and  square  posts  are  needlessly  strong  for  one  diameter,  insufficiently  so 
in  the  other.  When  the  pin  is  double,  as  in  bicuspids  and  molars,  round 
or  square  pins  may  be  employed. 

The  old  type  of  post,  the  wood  pivot,  has  been  so  entirely  super- 
seded that  it  scarcely  needs  description.     These  crowns  Avere  anchored  by 


THE  POST  AND  PLATE  CROWN.  607 

means  of  round  hickory  sticks,  which  were  compressed  immediately 
before  using.  A  suitable  crown  selected  was  ground  to  the  root  face,  the 
compressed  wood  set  in  its  base,  and  then  the  post  was  thrust  into  the 
enlarged  pulp-canal.  Roots  have  been  split,  frequently,  through  the 
swelling  of  the  compressed  wood. 

The  form  of  made-up  post  crowns  most  commonly  employed  is 
selected  as  the  typical  form  :  it  is  the  pin  and  plate  crown.  A  detailed 
description  of  this  will  serve  to  illustrate  many  of  the  principles  govern- 
ing the  making  of  all  crowns. 

The  method  of  making  is  as  follows  :  An  incisor  or  cuspid  root  which 
is  in  a  perfectly  healthy  state  is  thoroughly  sterilized,  and  the  apical 
foramen  hermetically  sealed  by  some  unchangeable  material  which  has 
been  coated  or  saturated  with  a  strong  antiseptic  ;  usually  a  gutta-percha 
point  is  used  for  this  purpose,  one  which  has  been  soaked  in  one  of  the 
antiseptic  oils. 

The  pulp-canal  is  enlarged  for  about  two-thirds  its  length,  in  such 
shape  as  to  receive  a  flattened  pin  of  iridio-platinum  wire  of  No,  14 
B.  &  S.  gauge,  which  is  to  fit  the  enlarged  canal  easily  enough  to  permit 
ready  removal. 

Fig.  746.         Fig.  747.  Fig.  748.  Fig.  749. 


The  face  of  the  root  is  shaped  to  follow  the  outline  of  the  gum 
margin,  and  to  have  its  surface  about  a  line  below  this  margin  (Fig. 
747).  At  its  anterior  aspect  the  cutting  should  be  a  trifle  deeper  than 
at  the  other  parts,  to  ensure  perfect  hiding  of  the  joint.  The  operator 
may  now,  if  he  prefers,  take  an  impression  of  the  face  of  the  root,  and 
fit  the  root-plate  on  a  model  prepared  from  it.  An  effective  method  is 
as  follows  :  After  shaping  the  post-canal  and  face  of  the  root  and  fitting 
the  post,  Mellotte's  moldine  is  placed  around  the  pin,  covered  by  damp 
tissue-paper,  and  inserted  in  the  root ;  an  impression  in  moldine  is  then 
taken ;  after  removing  from  the  mouth  the  post  is  withdrawn  and  placed 
in  position  in  the  impression,  and  a  die  of  fusible  metal  made.  Should 
the  paper  and  moldine  be  scraped  from  the  post  in  removing  it  from  the 
canal,  it  is  to  be  again  covered  by  moldine  enclosed  in  the  paper  before 
placing  it  in  the  impression. 

The  thin  layer  of  moldine  covering  the  post  permits  its  withdrawal  from 
the  die.  A  small  piece  of  soft  platinum  plate  No.  31  or  24-carat  gold 
plate  No.  30  is  well  annealed  and  placed  upon  the  root  face  represented 
on  the  die,  and  pressed  into  rough  adaptation  (Fig.  746) :  a  piece  of 
erasing  rubber  answers  well  as  an  elastic  counter-die  for  this  purpose.  A 
buckshot  or  a  small  piece  of  soft  lead  is  placed  over  the  root  face  on 
the  die,  and  struck  with  a  hammer  until  it  is  fit  to  serve  as  a  counter-die. 


608 


ARTIFICIAL   CROWNS. 


The  small  plate,  again  annealed,  is  placed  between  die  and  counter 
and  swaged  with  a  light  hammer.  A  hole  is  made  in  the  plate  to  un- 
cover the  root  opening,  small  enough  to  require  force  in  pushing  the  post 


Fig.  750. 


through  it,  so  that  the  post,  when  in  position,  is  closely  embraced  on  all 
sides.  The  post  is  then  withdrawn,  the  plate  coming  with  it ;  borax  is 
applied  at  the  line  of  junction,  and  if  the  plate  is  platinum  it  is  soldered 
with  a  small  piece  of  24-carat  gold,  or,  if  the  plate  be  of  gold,  with  a 


Fig.  751. 


Fig.  752. 


minute  piece  of  22-carat  solder.  The  plate  is  then  trimmed  to  follow 
the  root  outline ;  at  its  labial  aspect  it  is  filed  to  a  thin  edge  (Fig.  748). 

The  post  and  plate  are  placed  in  position  on  the  natural  root,  and 
with  an  orange-wood  stick  and  a  light  mallet  tapped  at  all  points  until 
the  adaptation  is  perfect. 

A  bite  of  wax  which  includes  the  adjoining  teeth  is  now  taken,  re- 
moved, and  chilled. 

Next  a  plaster  impression  is  secured,  in  which  are  withdrawn  the 
post  and  plate ;  if  not  withdrawn  in  the  impression,  a  depression  is  seen, 
in  which  the  top  of  the  pin  is  inserted. 

A  shade  tooth  is  selected  at  this  time.  The  impression  is  double 
varnished  with  thin  shellac  and  thin  sandarac,  allowing  each  varnish  to 
dry  well.  Pins  are  placed  in  the  impressions  of  the  teeth  adjoining  the 
root  to  be  crowned,  and  poured  carefully  with  rather  thin  plaster,  to  be 
sure  the  impressions  of  the  tips  of  the  teeth  are  perfectly  filled.  Let  this 
set  well  before  separating  the  model  from  the  impression  ;  place  the 
wax-bite  in  position  on  the  model,  and  make  an  articulation  on  a  crown 
articulator. 


COLLAR  CROWNS.  609 

Varnish  with  thin  shellac  the  teeth  of  the  models. 

Saw  off  the  protruding  end  of  the  post  to  within  one-sixteenth  of  an 
inch  of  the  plate ;  the  anterior  edge  of  the  post  may  be  bevelled  even 
with  the  plate ;  removing  more  than  this  weakens  the  post  attachment 
to  the  plate. 

A  plain  plate,  straight  pin   tooth,  having  a  shape,  size,  and   color 
corresponding  with   the  adjoining  tooth,  is  then  selected.     Sti-aight  pin 
teeth  are   stronger  than  than  those  with  cross  pins;  but  the 
lower  pin  must  be  in  such  situation  that  it  will  not  be  ground     Fig.  753. 
out  in  the  fitting.     Grind  the  tooth  with  fine  grit  corundum 
wheels  until  the  cervical  portion  fits  perfectly  the  outer  edge 
of  the  plate  and  has  the  same  contour  :  the  cutting  edge  should 
be  precisely  on  a  line  with  its  fellow  and  restore  the  general 
curve  of  the  incisors,  repairing  the  break  of   the   arch  line. 

Bevel  the  palatal  aspect  from  about  one-eighth  of  an  incli 
beneath  to  the  cutting  edge,  and  bevel  the  porcelain  beneath 
the  lower  pin  to  expose  the  head  of  the  post  (Fig.  753). 
Make  a  small  plaster  wall  to  hold  the  tooth  while  fitting 
the  backing  stay. 

Should  the  tooth  be  a  little  too  blue  in  color,  use  24-carat  plate  for 
backing ;  if  a  trifle  yellow,  use  platinum  plate. 

A  closer  adaptation  of  the  backing  may  be  made  by  using  well- 
annealed  plate  of  No.  35  gauge,  and  placing  over  this  plate  of  No.  28 
or  27  gauge.  The  thin  plate  should  be  well  burnished  over  the  entire 
palatal  aspect,  and  turned  under  at  the  cervical  portion.  The  stay 
should  extend  clear  to  the  cutting  edge  of  the  tooth  to  ensure  protection 
to  the  porcelain  during  mastication  (Fig.  749).  With  a  wedge-shaped 
chisel  split  the  pins  and  turn  back  the  sections,  so  that  the  backing  is 
firmly  held.  Boil  the  tooth  and  plate  in  pickling  fluid  ;  place  in  posi- 
tion on  the  model ;  unite  plate  and  tooth  with  adhesive  wax. 

Remove  from  the  model  and  invest  in  sand  and  plaster.  The  removal 
from  the  model  without  deranging  the  parts  may  be  readily  effected  as 
follows :  At  the  palatal  aspect  cut  away  the  plaster  of  the  model  until 
the  post  is  exposed  (Fig.  750) ;  the  fixture  may  then  be  pushed  out  by 
pressure  on  the  end  of  the  post.  The  piece  is  then  invested  in  sand 
and  plaster  (Fig.  751). 

When  the  investing  material  has  set,  remove  the  adhesive  wax  ; 
fill  the  V-shaped  space  between  tooth  and  plate  with  thin  pieces  of 
24-carat  plate ;  apply  borax ;  cover  with  small  squares  of  20-carat 
solder  ;  dry  out ;  then  heat  slowly  from  the  investment  side  ;  when  the 
tooth  shows  red  by  heat  transmitted  through  the  investment,  turn  the 
fine  blowpipe  flame  on  the  plate  and  backing,  and  the  soldering  will  be 
perfect.  Cool  gradually  ;  pickle  and  finish  with  all  the  care  a  jeweller 
exercises  in  the  finish  of  his  work.  The  outlines  of  the  crown  should 
then  be  in  exact  correspondence  with  the  outlines  of  the  root  (Fig.  752). 

Collar  Crowns. 

The  second  class  of  crowns  are  those  in  which  retention  is  by  means 
of  encircling  collars  or  bands.  As  the  band  is  the  distinctive  feature  of 
this  class,  it  will  be  first  described. 

39 


610  ARTIFICIAL  CROWNS. 

The  first  requisite  of  this  band  is  that  it  shall  fit  absolutely,  not 
approximately.  Faults  in  this  direction  are  the  most  common  and  those 
to  be  most  guarded  against.  The  second  requisite  is  that  these  bands 
shall  not  be  irritating  to  the  vital  parts,  and  yet  shall  offer  a  perfect 
protection  against  the  ingress  of  pathogenic  organisms  or  their  products 
to  the  parts  we  design  to  protect.  This  implies  that  the  band  shall  not 
impinge  on  the  pericementum,  nor  must  it  have  any  roughened  edge  or 
surface  to  irritate  the  overlying  gum.  It  should  extend  to  such  depth 
beneath  the  gum  margin  that  the  gingival  margin  shall  form  a  barrier, 
not  the  wall  of  a  pocket.  The  band  should  grasp,  but  not  irritate;  a 
trifle  over  one-sixteenth  of  an  inch  in  depth  will  be  sufficient  in  the 
majority  of  cases. 

The  surface  having  the  greatest  sectional  area  should  be  at  the  edge 
of  the  collar  or  barrel.     This  requires  that  the  root  be  so  trimmed  that 

Fig.  754.  Fig.  755. 


Incisor. 


Outer  lines  represent  original  con-  Molar, 

tour ;  inner  lines,  the  form  to  re- 
ceive barrels  or  ferrules.  Patterns  for  collars. 

its  walls  are  at  least  parallel  (Fig.  754).  It  will  save  the  patient  dis- 
comfort and  the  operator  material  if  after  shaping  the  root  an  accurate 
impression  of  the  parts  be  taken.  On  a  model  made  from  this  impres- 
sion a  pattern,  following  the  gum  line,  should  be  shaped.  From  this 
pattern  a  piece  of  plate  is  cut,  22-carat,  No.  29  or  30  (Fig.  755).  This 
is  annealed  and  bent  to  fit  the  root  or  tooth  on  the  model. 

Annealed  and  transferred  to  the  mouth,  the  band  is  pressed  into  close 
adaptation,  and  a  scratch  made  indicating  the  amount  of  overlapping  of 
the  edge.  Remove  this  and  cut  a  trifle — say  one-twentieth  of  an  inch — 
beyond  the  scratch  to  allow  for  stretching.  File  the  edges  square,  ajjply 
borax,  and  hold  them  in  firm  contact  with  one  another,  either  by  use  of 
binding  wire  or  by  overlapping  the  edges,  and  then  bringing  back  into 
direct  contact,  so  that  they  will  be  held  together  by  the  elasticity  of  the 
metal  itself.  Place  on  the  inside  of  the  collar  a  small  piece  of  20-carat 
solder,  and  fuse  by  holding  in  a  small  Bunsen  or  large  alcohol  flame. 

Another  method  of  fitting  the  collars  is  as  follows  :  The  perimeter  of 
the  root  is  taken  by  means  of  annealed  brass  wire  of  No.  33  gauge.  The 
ends  of  the  wire  are  passed  through  the  end  openings  of  a  dentimeter, 
one  end  being  caught  fast  upon  the  side  pin  of  the  instrument,  and  by 
drawing  upon  the  loose  end  the  nose  of  the  dentimeter  is  drawn  to 
within  an  eighth  of  an  inch  of  the  outer  face  of  the  root,  when  the 
instrument  is  turned,  twisting  the  wire  and  drawing  it  closely  about 
the  neck  of  the  teeth.  The  opposite  edge  of  the  wire  loop  is  held  down 
by  means  of  an  instrument  to  prevent  it  slipping  off*  the  root. 


COLLAR  CROWNS. 


611 


The  loop  is  removed  (Fig.  756)  and  divided  at  a  point  opposite  the 
twist  and  straightened.     The  line  of  greatest  distance  between  the  gum 
line  of  the  root  to  be  crowned  and  the  antagonizing  tooth  is  measured, 
and  a  rectangle  of  plate  of  that  width  and  the  length  of  the 
straightened  wire  is  cut.     Should  the  area  of  the  root  face  be    Fig-  "56. 
noticeably  less  than  that  to  be  filled  by  the  articulating  face  of 
the  crown,  the  plate  is  to  be  cut  in  the  form  of  a  trapezoid,  its 
short  parallel  side  somewhat  shorter  than  the  length  of  the 
wire.       The  ends  to  be  joined  are  filed  perfectly  square  and 
covered  by  borax  and  soldered. 

The  cylinder  may  be  then  placed  upon  an  appropriate  man- 
drel, and  pressed  up  on  it  until  it  fits  tightly,  giving  an  approx- 
imate form  to  the  cylinder. 

If  the  operator  prefer  he  may  employ  a  seamless  gold  collar 
procured  from  the  manufacturer,  and  form  this  upon  a  man- 
drel (Fig.  757).  Making  a  soldered  cylinder  for  each  case  is, 
however,  a  more  precise  method ;  moreover,  it  permits  of 
making  the  circumference  of  one  edge  of  the  collar  greater 
than  that  of  the  other  when  this  difference  in  the  sizes  is 
demanded. 

The  exact  neck  forms  may  be  given  in  the  following 
manner :  Lay  the  wire  loop  as  it  comes  from  the  tooth  upon 
a  smooth  flat  lead  surface,  and  place  over  it  an  old  tool- 
handle  sawn  square  and  given  a  smooth  surface.  Strike  the 
wood  a  hard  blow,  driving  the  wire  into  the  lead  and  wood, 
leaving  both  lead  and  wood  marked  by  the  outline  form  of 
the  wire  (Fig.  758).  The  wire  is  straightened,  the  gold 
measured,  and  the  cylinder  made  as  described.  It  is  then 
bent  to  fit  the  indentation  made  by  the  wire  in  the  wood, 
and  next  further  adapted  to  the  groove  in  the  lead.  It  is 
then  transferred  to  the  root  in  the  mouth,  the  outline  of  the 
gum  margin  marked  on  its  surface,  and  the  collar  trimmed 
to  this  line. 

It  is  set  upon  the  root  until  one  portion  of  it  touches  the 
gum,  when  the  outline  to  which  the  edge  of  the  collar  must 
be  cut  is  noted,  so  that  it  shall  be  at  a  uniform  depth  below 
the  gum  line.  The  collar  is  cut  to  this  line,  transferred  to  the 
root  or  tooth,  and  pushed  into  position. 

Subsequent  manipulations  depend  upon  the  class  of  tooth 
to  be  replaced,  for  there  are  many  modifications  of  the  sub- 
sequent operations  depending  upon  whether  the  tooth  has  or 
has  not  a  vital  pulp,  and  whether  the  root  is  that  of  an 
incisor,  cuspid,  bicuspid,  or  molar. 

As  the  molar  is  the  commonest  of  barrel  crowns,  it  will 
be   described    first.       There    are    many    time-saving    methods 
recommended  and  applied  in  the  inaking  of  these  crowns,  but 
in  most  of  them  time-saving   is  at  the    expense 
results. 

The  following  is  a  method  devised  about  ten  years  ago  by  the  writer, 
and  followed  ever  since  to  the  exclusion  of  all  others  :  The  band  is  first 
made  as  described  above,  and  cut  down  to  within  an  eighth  of  an  inch  or 


of  esthetic  ^;^^"- 


612 


ARTIFICIAL  CROWNS. 


Fig.  757. 


No.  1. 


No.  2.  No.  3.  No.  4.  No.  5.  No.  6. 

Mandrels  for  shaping  seamless  tooth-root  collars. 


No.  7 


COLLAR   CROWNS. 


613 


so  short  of  occlusion,  leaving  a  square  edge.  A  wax-bite  is  taken  on  this, 
including  two  or  three  adjoining  teeth  and  removed.  A  plaster  impres- 
sion is  then  taken,  in  which  the  barrel  is  imbedded  and  withdrawn.     A 

Fig.  768. 


model  and  articulating  model  are  made  and  mounted,  preferably  on  a 
Bonwill  articulator,  but  usually  upon  the  crown  articulator,  as  in  Fig.  759. 
While  the  barrel  is  upon  the  plaster  model  the  walls  are  to  receive  their 
correct  contour.     The  catalogues  of  the  manufacturers  exhibit  an  ever- 

FiG.  759. 


growing  list  of  pliers  designed  for  this  purpose.  The  two  forms  figured 
subserve  all  the  needs — one  the  form  known  as  the  Johnson  pliers  (Fig. 
761).  The  curves  of  short  radius  maybe  given  collars  with  these.  The 
second  pair  is  made  by  bending  the  beaks  of  a  pair  of  round-nose  pliers 
(see  Fig.  379) ;  the  curve  given  the  jaws  represents  the  average  curve 
of  the  buccal  walls  of  the  natural  teeth. 

The  contouring  is  done  before  the  barrel  has  been  removed  from  the 
model,  as  the  cervix  is  held  in  shape  by  the  plaster  and  the  barrel  suffers 
no  change  of  shape  at  that  part.  The  occluding  teeth  are  varnished  and 
oiled  slightly,  the  barrel  filled  with  soft  plaster,  and  the  occlusion  made. 
When  the  plaster  has  set  it  is  to  be  trimmed  to  expose  the  square  shoul- 
der made  by  the  top  of  the  band  and  scraped  down  uniformly  to  the 
thickness  of  No.  30  plate.  Cusps  and  sulci  are  then  carved  in  such  a 
manner  as  to  get  the  greatest  amount  of  masticating  surface  and  natural 
effect. 

Natural  teeth  of  the  same  class  should  form  the  models  from  which 
to  copy. 


614 


ARTIFICIAL  CROWNS. 


The  surface  plaster  at  completion  of  the  carving  is  short  enough  to 
allow  for  the  thickness  of  plate  used  for  the  cap.  The  collar  and  plaster 
cusps  are  then  imbedded  in  plaster  to  a  level  with  the  shoulder ;  when 

set,  this  plaster  is  cut  to  a  tapering 
prism  or  a  truncated  pyramid  (Fig. 
761,  A). 

Varnish  and  make  a  Babbitt  metal 
die ;  this,  driven  into  a  block  of  soft 
lead,  makes  its  counter. 

Annealed  22-carat  plate,  No.  29 
gauge,  is  swaged  between  die  and  coun- 
ter-die and  the  surplus  gold  X  B  trimmed 
oif.  The  junction  of  this  cap  with  the 
barrel  forms  then  but  a  line ;  pickle  the 
sections ;  apply  borax  to  the  inner  sur- 
face of  the  cap  and  the  top  of  the 
band ;  hold  them  in  apposition  with 
binding  wire  or  between  the  jaws  of 
self-closing  pliers,  and  solder  with  20- 
carat  solder  over  a  Bunsen  flame.  When 
finished  there  are  but  two  faint  lines  rep- 
resenting the  two  joints  of  the  piece  (C). 

Fig.  761. 


The   die  for   swaging  the  cap  may  be  more  quickly  made  with  Dr. 
Mellotte's  devices  of  tray,  ring,  moldine,  and  fusible  alloy. 

A  small  tray  is  filled  with  moldine,  the  surface  of  the  latter  is  flat- 
tened ;  the  plaster  cusps  are  pressed  into  the  moldine  until  the  collar 
leaves  a  distinct  and  perfect  outline.  The  rubber  ring  is  placed  around 
the  tray,  forming  a  well,  the  crown  imprint  in  its  bottom.  A  die  of 
fusible  metal  is  then  formed.  Another  method  almost  exact  is  to  fill 
the  gold  barrel  with  soft  plaster  or  modelling  compound  while  the  bar- 
rel is  in  the  mouth,  and  direct  the  patient  to  bite  into  it,  then  perform 
the  movements  of  mastication.  The  crown  is  removed  from  the  root, 
tlie  plaster  or  modelling  compound  scraped  away  the  thickness  of  No. 
30  plate,  and  a  die  formed  as  above  described. 


COLLAR  CROWNS. 


615 


These  appliances  of  Dr.  Mellotte  are  invaluable  in  many  small 
laboratory  operations. 

But  few  of  the  many  methods  advanced  secure  the  accuracy  of  adap- 
tation of  cap  to  root  and  of  articulation  which  would  warrant  their 
general  endorsement. 

With  a  view  to  making  an  artificial  crown  what  it  should  be,  an 
instrument  for  the  restoration  of  a  lost  function,  it  will  be  seen  that 
accuracy  of  articulation  is  an  essential.  The  exposure  of  the  least  sur- 
face of  solder  is  desirable  from  aesthetic  considerations. 

Should  it  be  desired  to  use  this  form  in  replacing  bicuspids,  porcelain 
faces  may  be  attached  after  the  following  method,  and  the  same  may 
apply  in  making  crowns  for  the  anterior  teeth  containing  vital  pulp 
which  it  is  decided  to  retain.  The  operation  in  nearly  all  cases  up  to  and 
including  the  mounting  of  the  articulation  is  the  same. 

The  labial  or  buccal  aspect  of  the  band  is  to  have  a  saw-cut  made  at  the 
cervix,  following  the  gingival  margin,  to  the  depth  of  the  thickness  of  a 
plain  plate  tooth  which  has  been  selected — if  a  bicuspid,  a  cross-pin  cus- 
pid is  used.  Vertical  cuts  are  made  from  the  top  of  the  band  joining 
the  saw-cut,  detaching  a  section  of  the  gold  (Fig.  762).     The  tooth  is 


Fig.  763.        Fig.  764. 


Fig.  765. 


ground  to  make  a  perfect  joint  at  the  cervical  shoulder  and  to  fit  the 
lateral  walls  of  the  barrel  (Fig.  763).  The  tooth  is  bevelled  for  one- 
fourth  of  an  inch  or  less  at  the  cutting  edge,  and  a  stay  of  24-carat 
gold  No.  29  fitted  to  extend  to  all  edges  of  its  back  (Fig.  764). 
This  stay  makes  a  close  joint 
with  the  sides  of  the  barrel.  The 
pins  are  to  be  split.  Pickle,  unite 
tooth  and  barrel  with  adhesive 
wax,  and  invest  in  sand  and  plas- 
ter, so  that  the  investment  repre- 
sents an  open  tunnel  (Fig.  765). 

Remove  the  wax,  apply  borax 
along  the  joints  and  around  the 
pins,  use  four  minute  pieces  of 
solder,  one  at  each  lateral  joint,  one  over  each  pin  ;  heat  gradually  to  a 
red  heat ;  then  turn  the  fine  blowpipe  flame  into  the  tunnel  and  unite 
the  parts.  The  subsequent  making  of  the  cap  is  as  described  for  the  all- 
gold  crown  ;  it  extends  to  the  top  of  the  backing,  which  is  at  the  cutting 
edge  of  the  tooth. 

Prepared  for  soldering,  the  cap  is  waxed  to  the  band,  and  the  piece 
invested  in  sand  and  plaster,  cap  down,  so  that  the  interior  of  the  crown 
represents  a  well  in  the  centre  of  the  investment ;  the  investment  over 
the  cap  should  form  but  a  thin  layer. 

Solder  sufficient  to  fill  the  joints  well  is  boraxed  and  placed  in  the 


616  ARTIFICIAL  CROWNS. 

cap.     The  piece  is  heated.     Transferred  to  the  charcoal,  the  blowjiipe 

flame  is  directed  against  the  base  of  the  investment  until  the  solder 

-„„       flows.     When   cool  it  is  boiled  in  acid,  and  every  joint  is 

dressed  down  with  small  files  and  corundum  pencils   until 

smooth ;  then  bufled,  burnished,  and  polished  (Fig.  766). 
A  similar  process  may  be  used  for  the  anterior  teeth,  as 

described  on  p,  618  for  those  cases  in  which  it  is  thought 

advisable  to  retain  a  vital  pulp. 
Occasionally,  where  there  is  not  a  suflicient  amount  of  a  broken 
bicuspid  extending  above  the  gum  line  to  aiford  adequate  support  to  a 
collar  crown,  a  post  is  attached  to  either  the  root  itself  or  made  part  of 
the  crown.  If  anchored  in  the  root,  the  pin  is  made  after  the  form  of 
an  inverted  U,  and  securely  fastened  by  means  of  amalgam.  If  it  is  de- 
signed to  attach  the  pin  to  the  crown,  the  pulp-canal  is  enlarged  for  half 
its  length  ;  if  the  root  has  a  bifurcated  or  double  canal,  the  palatal  root 
is  reamed  out  to  that  depth.  An  iridio-platinum  post  is  set  in  the  canal 
and  the  collar  adjusted.  A  wax-bite  and  plaster  impression  are  taken,  a 
model  and  artic^ulation  made.  The  collar  face  is  cut  out  for  the  reception 
of  the  porcelain  tooth,  and  the  post  is  loosened  from  its  plaster  canal. 
The  facing  is  fitted  and  a  stay  adapted  ;  adhesive  wax  unites  the  facing 
to  the  collar  and  the  post  to  the  backing  stay.  The  pieces  are  next  with- 
drawn, invested,  giving  the  investment  the  tunnel  form  of  Fig.  766,  but 
the  investment  is  carried  over  the  pin  sufficiently  to  hold  it.  The  cap  is 
formed  and  fitted  as  described,  attached  to  the  collar  and  facing  by 
means  of  wax,  and  invested  in  an  inverted  position,  carrying  the  invest- 
ment up  on  the  pin,  but  leaving  space  enough  between  the  post  and 
palatal  portion  of  the  collar  to  permit  the  ready  introduction  of  the 
solder.  The  investment  overlying  the  cap  should  be  thin.  When  this  has 
set  the  wax  is  removed ;  a  liberal  amount  of  borax  and  sufficient  solder 
are  applied  to  fill  the  cap.  The  piece  is  heated  and  the  solder  flowed  by 
directing  a  flame  against  the  base  of  the  investment. 

Another  method  of  attaching  porcelain  facings  to  the  gold  barrel 
crown  is  by  making  the  entire  crown  first  of  gold,  the  barrel  and  articu- 
lating surface  complete.  The  external  wall  of  the  erown  has  the  seg- 
ment made  visible  by  the  movements  of  the  lips  sawn  out,  and  the  cut 
edges  of  the  metal  bevelled,  A  porcelain  facing  is  selected  of  a  size  to 
fit  the  space  with  the  minimum  grinding.  It  is  to  be  ground  in  until  all 
of  its  edges  fit  those  of  the  barrel.  A  stay  of  No.  34  pure  gold  is  bur- 
nished over  the  back  of  the  porcelain  tooth.  The  edge  of  the  stay 
should  be  accurately  adapted  to  the  barrel.  The  crown  and  facing  are 
cemented  together  with  adhesive  wax,  covered  by  a  thin  investment  and 

soldered  by  means  of  a  blowpipe  flame 
^^'J^\  ^  ^     .-.r^        directed  against  the  portion  of  the  in- 
vestment covering  the  facing. 

The  buccal  and  articulating  faces 
of  molars  and  bicuspids  ,  may  be 
made  of  porcelain,  the  attachment  of 
the  crown  to  the  root  being  secured  by  means  of  a  gold  barrel.  The  barrel 
is  made  as  for  an  all-gold  crown,  A  wax-bite  and  impression  are  taken, 
and  an  articulation  mounted.  Before  cutting  away  the  buccal  wall  of  the 
barrel  for  the  reception  of  the  porcelain,  measure  by  means  of  a  wire  and 


COLLAR  CROWNS.  617 

dentimeter  the  circumference  of  the  upper  portion  of  the  barrel.  The 
loop  made  is  taken  to  the  d6p6t,  and  a  saddle-back  or  a  plain  rubber 
tooth  is  selected,  the  circumference  of  which  agrees  with  that  of  the  barrel 
(the  wire  loop).  The  tooth  should  have  but  little  thickness  of  porcelain 
above  the  pins  (Fig.  768) ;  the  S.  S.  W.  cusp  crowns  are  designed  for 

Fig.   768. 


Cusp  crowns. 

this  special  use.  A  scratch  is  made  along  the  buccal  portion  of  the 
barrel,  marking  it  slightly  above  the  gum  line  and  between  the  adjoining 
natural  teeth  along  the  line  of  exposure.  A  fine  saw  is  used  to  cut  away 
the  buccal  walls  to  these  lines.  The  palatal  wall  of  the  barrel  is  cut 
down  if  necessary  to  admit  the  face,  so  that  it  will  articulate  with  the 
antagonizing  teeth.  Should  there  be  any  lack  of  correspondence  between 
the  outlines  of  the  barrel  top  and  the  cusp  crown  or  tooth,  the  gold  is 
bent  to  fit  the  latter  accurately.  By  means  of  fine-grit  corundum  wheels 
the  edges  of  the  porcelain  are  closely  adapted  to  the  cut  edges  of  the 
gold  at  the  cervical  and  approximal  borders,  and  articulated  perfectly 
with  the  antagonizing  teeth.  The  tooth  and  barrel  may  now  be  set  with 
cement :  it  is  preferable,  however,  to  solder  the  porcelain  to  the  barrel. 
A  piece  of  24-carat  gold  No.  33  is  fitted  as  a  stay  to  the  under  surface  of 
the  porcelain  and  burnished  into  accurate  contact.  The  tooth  and  stay 
are  set  in  the  barrel,  and  the  latter  is  cut  away  at  points  interfering  with 
its  correct  placement.  It  is  boiled  in  the  acid  solution,  and  invested  so 
that  the  interior  of  the  barrel  and  the  stay  exposed  form  a  well.  Borax 
is  painted  around  the  line  of  junction  and  over  the  pins,  a  small  piece  of 
solder  placed  over  each  pin,  and  three  or  four  pieces  around  the  joint, 
and  the  piece  is  gradually  raised  to  a  high  heat ;  a  fine  flame  directed 
into  the  well  fuses  the  solder,  uniting  the  pieces  perfectly. 

In  finishing  the  crown  the  gold  should  be  dressed  down  to  the  porce- 
lain, making  a  perfectly  smooth  joint.  No  projection  of  the  gold  beyond 
the  surface  of  the  porcelain  should  remain. 

Fused  porcelain  may  be  used  in  lieu  of  solder  to  attach  the  crown 
to  the  barrel,  as  described  by  Dr.  Robert  Huey  :  ^  "  The  barrel  is  fitted 
and  cut  out  as  described.  One  of  Ash  &  Sons  diatoric  teeth  is  selected 
and  fitted  to  the  barrel.  Openings  are  drilled  through  the  mesial  and 
distal  walls  of  the  barrel,  which  shall  exactly  uncover  the  openings  of 
the  tube  in  the  tooth.  A  piece  of  platinum  wire  is  thrust  through  holes 
and  tube,  holding  the  porcelain  to  the  gold.  The  platinum  wire  is  now 
either  riveted  or  soldered  to  the  barrel.  The  line  of  junction  between 
gold  and  porcelain  is  painted  with  a  paste  of  dental  glass,  which  is  then 
fused  in  a  Downie  furnace." 

1  Penna.  State  Dental  Soc,  1896. 


618  ARTIFICIAL   CROWNS. 

Porcelain-faced  Crowns  for  Teeth  containing  Vital  Pulps. 

When  collar  supports  are  to  have  porcelain  faces,  those  cases  where 
crowns  are  to  be  placed  over  teeth  containing  vital  pnlps,  the  tooth  to  be 
„      _^Q  crowned  is  to  be  trimmed  so  that  a  sufficient  covering  of 

/v    ^'       '  dentine  is  left  to  act  as  a  protector  to  the  pulp.     At  the 

/|  \  labial  or  buccal  aspect  the  tooth  is  sloped  to  the  gum  mar- 

/  1  \       A,  gin,  carefully  avoiding  uncovering  the  cornua  of  the  pulp 

I  m  \  ll  Jwik  C^^S-  '^^'^^  ^)-  The  root  is  trimmed  for  the  reception  of  a 
■\r"J  pP—l  collar,  which  is  fitted  and  permitted  to  project  about  one- 
1  ^^  sixteenth  of  an  inch  above  the  edges  of  the  tooth.     The 

v./'  parts  of  the  band  in  contact  with  the  antagonizing  teeth 

""  when  the  jaws  are  closed  are  ground  to  about  one-sixteenth 

of  an  inch  short  of  occlusion.  The  labial  portion  of  the  band  is  cut  away, 
following  the  slope  given  the  labial  aspect  of  the  tooth  and  level  with  it. 
A  cross-pin  tooth  is  carefully  adapted  to  these  edges.  The  palatal  surface 
of  the  porcelain  tooth  is  given  a  long  bevel  toward  its  cutting  edge.  A  stay 
of  No.  27  plate  is  closely  adapted  to  the  tooth,  its  lower  edge  in  contact  with 
the  collar  (Fig.  770).  The  tooth  and  barrel  are  invested  ;  the  pins 
Fig.  770.  are  soldered  to  the  stay,  and  the  stay  to  the  collar.  The  crown  in 
this  condition  is  transferred  to  the  model  and  the  articulation 
noted.  If  the  collar  is  almost  in  contact  with  the  antag- 
onizing teeth,  its  palatal  surface  is  formed  of  a  single  piece  of 
plate  bent  to  conform  to  the  open  top  of  the  collar,  and  as  far 
up  on  the  stay  as  the  bite  will  permit.  It  is  desirable,  where 
possible,  that  the  stay  should  be  made  double  throughout. 

Should  there  be  a  necessity  for  contouring  the  palatal  surface  of  the 
crown,  the  articulating  teeth  are  varnished,  a  batter  of  plaster  is  placed 
in  the  collar  and  over  the  stay  of  the  crown,  and  the  articulation  closed. 
The  plaster  is,  when  hard,  scraped  down  uniformly  to  allow  for  the 
thickness  of  the  piece  to  be  added — No.  30  plate.  It  is  then  carved  to 
the  desired  form,  freeing  from  plaster  the  edges  of  stay  and  collar.  A 
small  die  is  made  of  fusible  metal  poured  in  moldine  and  a  cap  swaged. 
The  pieces  are  boiled  in  acid.  The  surfaces  to  be  united  are  touched  with 
flux  wax  and  brought  together,  and  the  piece  invested.  Along  the  joint — 
or,  rather,  beneath  the  joint  on  the  collar — three  small  pieces  of  solder  are 
placed,  one  in  the  middle,  one  on  each  side.  In  soldering  direct  a  fine  flame 
beneath  the  joint,  never  on  the  cap,  as,  this  being  the  portion  most  readily 
heated,  the  solder  has  a  tendency  to  run  from  the  collar  to  the  surface  of 
the  cap.  In  finishing  such  caps  each  edge  should  be  carefully  rounded. 
Application  to  Abraded  Teeth. — This  form  of  crown  is  frequently 
applicable  to  abraded  teeth.  The  remaining  teeth  of  a  denture  being 
worn  down  to  within  a  short  distance  of  the  gum  line,  it  becomes  neces- 
sary to  protect  each  tooth  from  further  progress  of  this  formidable 
destruction.  Each  remaining  tooth  is  to  have  its  crown  length  restored 
by  the  substitute.  The  molars  and  bicuspids  are  covered  by  all-gold 
crowns ;  where  possible  the  anterior  crowns  are  made  with  porcelain 
faces,  without  destroying  the  receding  pulps. 

It  is  advisable,  first,  to  make  and  set  three  crowns — one  on  each  side 
and  a  central  incisor :  these  fix  the  bite  in  its  altered  relations ;  the 
remaining  crowns  are  then  fitted  and  adjusted  in  pairs. 


POST  AND  COLLAR  CROWNS. 


619 


Post  and  Collar  Crowns  (Richmond  Crowns). 

When  it  has  been  determined  that  the  use  of  a  band  upon  one  of  the 
anterior  teeth  is  desirable,  whether  from  undue  loss  of  tooth-substance 
or  because  an  unusual  stress  is  to  be  borne  by  the  root,  the  Richmond  or 
collar  crown  is  the  one  commonly  employed. 

A  band  is  made  to  fit  the  properly  shaped  root  according  to  the  method 
described.  This  is  placed  on  the  root,  and  is  trimmed  a  little  below  the 
margin  of  the  gum.  At  the  palatal  aspect  the  trimming  need  not  be  so 
deep.  The  curve  at  the  cervix  should  be  the  same  as  that  of  the  ad- 
joining tooth  (see  Figs.  722,  723),  so  that  in  the  completed  crown  the 
cervical  outlines  may  be  alike.     The  collar  is  then  removed,  pickled,  and 

Fig.  771. 


its  upper  surface  laid  upon  a  flat  piece  of  24-carat  gold  plate  No.  31,  the 
points  of  junction  boraxed,  a  minute  particle  of  solder  (22-carat)  placed 
at  the  junction  ;  the  plate  is  held  over  a  Bunsen  flame  until  the  solder 
flows  and  fixes  the  band  at  one  point.  The  plate  is  then  bent  down  to  fit 
the  entire  edge  outline  of  the  band,  and  soldered  as  before,  using  a  piece 
of  solder  of  the  size  of  a  pin's  head  for  this  purpose.  The  cap  is  then 
trimmed,  placed  in  position  upon  the  root,  an  opening  made  uncovering 
the  root-canal,  and  a  pin  which  has  been  fitted  thrust  through  this  open- 
ing into  position.  Withdraw  the  post,  and,  if  the  collar  comes  with  it, 
unite  them  with  a  small  piece  of  18-carat  solder ;  the  soldering  may  be 
done  over  the  Bunsen  flame.  As  a  rule,  it  is  necessary  to  unite  the  wire 
and  cap  by  means  of  adhesive  wax  to  enable  the  operator  to  withdraw 
both  pieces  together.  They  are  to  be  invested,  and  the  post  attached  to 
the  cap  with  a  small  piece  of  solder.  Place  the  post 
and  collar  in  position,  and  take  a  wax-bite  and  plas- 
ter impression  as  for  the  post  and  plate  crown.  The 
subsequent  operations  are  the  same  as  those  in  making 
the  latter  forms  of  crown.     (See  ante.) 

The  three  varieties  of  crowns  described  are  those 
which  are  commonly  and  most  acceptably  used  as 
supports  in  bridge-work. 

A  removable  porcelain  facing  to  place  upon  a  post 
and  collar  base  has  been  devised  by  Dr.  W.  L.  Mason 
of  Red  Bank,  N.  Y.^ 

The  post  and  collar  are  made  as  described.     Dr. 
Mason's  device  consists  of  two  pieces — one  a  drop-forged  backing  of 
heavy  gold  plate,  which  has   a   triangular  slot  throughout  its  length, 

^  Dental  Cosmos,  Aug.,  1896. 


Fig.  772. 


620  ARTIFICIAL   CROWNS. 

the  base  of  the  triangle  in  the  body  of  the  backing  (Fig.  772).  The 
second  piece  is  a  porcelain  facing,  having  baked  in  the  longitudinal  axis 
of  its  lingual  face  a  triangular  platinum  bar,  which  readily  slips  into 
the  slot  of  the  backing.  A  portion  of  the  post  extends  beyond  the  cutting 
edge  of  the  tooth.  Both  teeth  and  backings  are  made  in  standard  sizes 
and  forms. 

The  tooth  is  slipped  into  its  backing,  and  both  are  ground  to  fit  the 
ferrule  tops.  The  backing  is  attached  to  the  ferrule  by  means  of  hard 
adhesive  wax.  When  the  latter  is  hard,  the  platinum  extension  is 
grasped  and  the  tooth  withdrawn  from  the  backing ;  the  metallic  pieces 
are  next  invested  and  united  to  one  another  by  means  of  solder.  The 
piece  is  now  chilled,  smoothed,  polished,  and  adjusted  to  the  root.  The 
lingual  surface  of  the  tooth  and  the  platinum  are  to  be  covered  with 
a  thick  solution  of  chloro-percha  and  slipped  into  position  ;  the  pro- 
truding platinum  is  sawn  off  and  the  edges  of  the  metal  are  burnished. 

Ready-made  Crowns. 

Of  the  ready-made  porcelain  crowns  there  are  two  varieties — first, 
those  designed  for  fixation  upon  a  post  which  is  previously  fastened  in 
the  root ;  second,  those  having  a  pin  baked  in  them.  To  the  first  class 
belong  the  Bonwill,  the  Foster,  and  the  How ;  in  the  second  class  are 
included  the  Logan,  the  Brown,  and  the  new  Richmond  crowns.  Crowns 
which  are  formed  and  adapted  by  means  of  sets  of  ready-made  appli- 
ances, such  as  the  Hollingsworth  and  the  mandrel  systems,  belong  to 
the  class  of  built-up  crowns.  The  crowns  of  How  and  of  Brown  are  no 
longer  manufactured. 

Of  all  the  ready-made  porcelain  crowns,  that  offering  the  widest 
range  of  application  is  the  Bonwill.     It  is  made  entirely  of  porcelain, 

and  is  perforated  for  the  passage  of  the 

Fig.  773.  ^        supporting  post  (Fig.  773).     At  its  bases 

it  is  concave,  the  upper  portion  of  the  per- 
foration formed  into  a  shape  which  pre- 
vents the  displacement  of  the  crown  after 
it  is  fixed  upon  its  post. 

The  edges  of  the  porcelain  are  designed 
to  rest  uniformly  upon  the  outer  edge  of 
the  prepared  root-surface.  An  eminently 
satisfactory  method  of  fitting  these  porcelain  crowns  is  as  follows  :  After 
the  root  face  has  been  trimmed  as  for  the  reception  of  any  post  crown, 
take  a  wax-bite  of  the  side  having  the  crownless  root,  and  then  a  plaster 
impression.  In  the  plaster  impression  a  model  of  fusible  metal,  one 
melting  at  about  150°  F.,  is  poured.  A  shade  tooth  is  selected,  and  an 
articulation  mounted.  A  crown  of  the  proper  form,  shade,  and  size  is 
selected.  Select  one  the  base  line  of  which  corresponds  closely  with  that 
of  the  root  outlines  represented  in  the  model.  By  means  of  fine-grit 
corundum  wheels  the  crown  is  well  adapted  to  the  edges  of  the  root 
face  and  correctly  articulated  with  the  antagonizing  teeth.  In  adjusting 
these,  and  indeed  all  post  crowns  where  the  roots  can  be  grasped  firmly 
by  thera,  the  Ottolengui  root  clamps  are  invaluable  (Fig.  774,  Nos.  126 
to  129).     A  pin  of  the  largest  size  admissible  (Fig.  776)  is  set  in  the  root- 


BEAJDY-MADE  CROWNS. 


621 


canal  and  the  crown  set  in  position  over  it  (Fig.  775).     Should  there  be 
lack  of  correspondence  between  the  directions  of  the  root-canal  axis  and 


Fig.  774. 


No.  126. 


No.  127. 


No.  128. 


No.  129. 


Fig.  776. 


Root-clamps  for  crown-work. 
Devised  by  Dr.  Otlolengui. 

the  perforation  of  the  crown,  the  post  is  to  be  bent  and  filed  until  the 
crown  slips  readily  over  it,  the  palatal  wall  of  the  tooth  perforation 
resting  against  the  post.     The  latter  is  withdrawn  __ 

from  the  root,  and  by  means  of  a  small  wheel  bur 
the  walls  of  the  root-canal  are  cut  to  a  semblance 
of  a  screw  thread. 

After  the  crown  edges  have  been  adapted  to  the 
root  face,  a  small  corundum  point  is  passed  around 
the  basal  concavity  of  the  crown,  removing  sufficient 
amount  of  the  porcelain  to  give  almost  a  featlier 
edge.  This  is  to  prevent  the  amalgam  at  the 
junction  from  being  reduced  to  a  thin  sheet,  which  might  be  broken, 
forming  a  space  at  such  points  in  which  fermenting  materials  might 
find  lodgement. 

Slow-setting  zinc  phosphate  is  mixed  and  a  small  pellet  carried  to 
the  end  of  the  root-canal,  and  the  post  pressed  firmly  into  it ;  the  crown 
is  then  passed  over  the  post  into  its  proper  position  and  permitted  to 
remain  until  the  cement  is  hard.  The  crown  is  removed  and  soft 
amalgam  is  packed  about  the  pin  and  root-canal  walls  for  about  half  the 
length.  The  remaining  amalgam  is  wrung  out  to  remove  the  excess  of 
mercury,  and  packed  in  small  pieces  about  the  post.  Place  the  crown 
over  the  post  for  assurance  that  the  post  has  not  changed  in  position. 
In  packing  the  amalgam  a  more  homogeneous  mass  is  made  by  using 
pellets  of  bibulous  paper,  as  recommended  by  Dr.  Bonwill,  to  compress 
the  mass  and  force  out  the  surplus  mercury.  A  fresh  mix  of  amalgam, 
wrung  half  dry,  is  banked  up  about  the  post,  and  when  more  than 
enough  to   fill  the   concavity  in  the   base  of  the   crown   has  been  so 


622 


ARTIFICIAL   CROWNS. 


Fig.  777. 


Fig.  778. 


packed,  the  crown    itself  is    firmly  and    steadily  pressed  into  position 
by  means   of  an  appropriate   crown-driver   until  the  junction  of  the 

crown  and  root  is  represented 
by  a  faint  blue  line.  Amal- 
gam, mixed  very  dry,  is  now 
packed  about  the  end  of  the 
pin  in  the  cavity  of  the  ar- 
ticulating face,  using  bibu- 
lous paper  to  express  any 
free  mercury  ;  when  this  cav- 
ity is  more  than  full  sponge 


Crown  adjusters. 


gold  is  rubbed  into  the  amal- 
gam until  it  ceases  to  be  amal- 
gamated, when  the  surplus  is 
removed,  dressing  the  amal- 
gam   flush   with    the    crown 
surface.      If    the    amalgam 
employed  contains  at  least  60  per  cent,  of  silver,  and  cut  in 
fine  grains,  it  will  be  well  hardened  at  the  end  of  the  ope- 
ration described.    It  must  be  well  hardened  before  the  crown 
is  subjected  to  the  stress  of  mastication  ;  otherwise  the  crown 
will  be  displaced.    The  writer  occasionally  defers  the  packing 
of  the  amalgam  about  the  end  of  the  pin  to  the  next  day, 
filling  the  articulating  surface  cavity  with  zinc  phosphate, 
permitting  this  to   set  and  hold  the  crown   in  position  for 
twenty-four  hours,  so  that  the  amalgam  supporting  the  crown 
may  set  perfectly    before  any  force  is  applied  to  it.      The 
cement  is  subsequently  removed  and  its  place  filled  with  soft 
amalgam,  which  is  well  compressed  by  means  of  bibulous 
paper ;  the  soft  portions  of  amalgam  then  cut  out,  and  the 
filling  completed  with  dry  amalgam,  packing  more  than  full, 
then  cutting  it  down  to  the  surface  of  the  tooth. 

In  applying  this  crown  to  the 
restoration  of  molars  a  post  is  to  be 
used  in  each  root.  For  the  upper 
molars  a  large-sized  post  is  used  in 
the  palatal  root,  and  smaller  ones  in 
the  buccal  roots.  These  may  be 
fixed  in  position  by  means  of  zinc 
phosphate  to  hold  their  distal  ends, 
as  described  above. 
The  How  screw  posts  will  be  found  frequently  applicable  with  the 
Bouwill,  as  with  other  crowns  of  the  same  class.  The  Gates,  Foster,  and 
How  dovetail  crowns  are  all  of  analogous  forms,  and  are  to  be  attached 
in  the  common  method,  a  screw  anchored  in  the  root,  which  has  been 
drilled  and  tapped  to  receive  it,  amalgam  filling  every  remaining  space 
in  the  root  and  crown  and  also  between  them.  Their  mode  of  applica- 
tion is  seen  in  the  illustrations. 

The  all-porcelain  crowns,  such  as  the  Foster,  Gates-Bon  will,  dovetailed 
crown  (Figs.  781  to  783),  and  others,  have  been  set  in  various  ways, 
prominent  among  which  has  been  the  use  of  solid-headed  screws ;  but 


Fig.  779. 


Fig. 


READY-MADE  CROWNS. 


623 


firmer  and  more  satisfactory  work  can  be  done  by  first  fixing  the  screw- 
post  in  the  root  (Fig,  785),  thus  permitting  the  crown  to  be  slipped 
over  the  end  of  the  post  and  properly  adjusted  to  the  root,  after  which 
the  cavities  in  both  root  and  crown  may  be  partly  filled  and  a  nut 


Fig.  781. 


Fig.  782. 


Fig.  783. 


Foster  crown. 


Gates-Bonwill  crown. 


Dovetailed  crown. 


screwed  on  the  end  of  the  post  to  condense  the  filling  and  firmly  secure 
the  crown  in  its  place.  These  appliances  are  very  simple.  They  con- 
sist of  a  nut-driver,  over  which  is  placed  a  split  tube  for  carrying  the 
nut.     (See  sectional  view.  Fig.  784.)     The  sole  object  of  this  tube  is  to 

Fig.  784. 


AA       A  B 

How  screw-posts 
(A,  with  nut). 


AA         A         B 

Headed  screws. 


Nut-driver  witli  split  tube. 

hold  the  nut  and  prevent  its  falling  into  the  mouth  or  on  the  floor  during 
the  process  of  attaching  or  detaching  it  from  the  post. 

The  nuts  and  nut-drivers  are  made  of  three  sizes  to  suit  the  How 
screw-posts  aa,  a,  and  b,  and  the  old  form  of  headed  screws,  which  are 
made  of  the  same  sizes  as  the  How  posts  with  nuts.  Fig.  785,  A 
and  B,  illustrates  the  application  of  the  double  screw  in  connection 
with  molar  crowns. 

The  next  class  of  crowns  is  composed  of  those  having  their  platinum 
posts  baked  in  them  :  they  are  the  Logan,  the  Brown,  and  the  new  Rich- 
mond crown. 

The  first  of  these  has  the  widest  range  of  application,  and  is  the  form 
in  most  general  use.  Being  composed  of  porcelain  alone,  and  having  no 
underlying  mass  and  backing  of  metal,  they  present  a  translucent  appear- 


624 


ARTIFICIAL   CROWNS. 


ance  not  to  be  had  with  those  forms  of  crown  which  are  built  up  in  part 
of  metal.     An  excellent  method  of  selecting  and  adapting  these  crowns 


Fig.  785. 
B 


Fig.  786. 


is  as  follows  :  The  root  face  is  trimmed  by  means  of  rotatory  files  or  the 
Ottolengui  root-facers  to  the  level  of  the  gum  margin.  The  canal  is 
sterilized,  and  the  upper  third  hermetically  sealed,  the  remainder  of  the 
canal  enlarged  to  about  one-sixteenth  of  an  inch  in  diameter.  A  wax- 
bite  is  taken,  including  several  of  the  adjoining 
teeth.  A  piece  of  iron  wire  one-half  of  an 
inch  longer  than  the  reamed  portion  of  the 
canal,  and  small  enough  to  slip  very  freely  in 
it,  has  its  end  bent  into  a  loop  and  the  canal 
portion  covered  with  gutta-percha,  Avhich  is 
then  oiled  and  slipped  in  the  root.  A  plaster 
impression  is  taken  in  which  the  coated  wire  is 
withdrawn,  and  a  model  made  of  fusible  metal 
melting  at  about  150°  F.  A  shade  tooth 
and  a  crown  corresponding  with  the  natural 
teeth  are  selected.  The  direction  of  the  axis 
of  the  root-canal  is  noted,  the  angle  which  it 
makes  with  the  root  face,  and  compared  with 
the  direction  of  the  axis  of  the  selected  crown  : 
not  infrequently  it  is  necessary  to  bend  the  pin  at  an  angle  with  the  axis 
of  the  crown  itself  (Fig.  786).  The  opening  in  the  root,  made  by  with- 
drawing the  gutta-percha  and  wire,  is  enlarged  sufficiently  to  receive  the 
post  of  the  crown. 

The  pin  is  bent,  if  necessary,  so  that  the  axis  of  the  crown  is  parallel 
with  that  of  the  natural  fellow,  bringing  the  cutting  edge  of  the  artificial 
crown  in  the  arch  of  the  natural  teeth.  The  points  of  contact  between 
the  edges  of  the  crown  and  the  face  of  the  root  represented  in  the  metallic 
model  are  ground  from  the  porcelain  until  there  is  a  uniform  contact 
throughout  the  crown  edge.  The  grinding  is  done  by  means  of  square- 
edged  corundum  wheels  on  a  laboratory  lathe  or  by  an  engine  wheel,  as 
shown  in  Fig.  787.  The  cutting  edge  of  the  artificial  crown  should 
exactly  repair  the  break  in  the  arch.  Its  palatal  surface  is  cut  away, 
if  necessary,  to  articulate  with  the  antagonizing  teeth,  in  which  event 
the  cut  surface  should  be  smoothed  and  polished.  The  canal  is  enlarged 
by  means  of  fissure  burs  or  Ottolengui's  reamers  (Fig.  788)  until  the 
pin  slips  readily  into  place  and  the  surfaces  of  crowns  and  root  are  in 
contact.  Should  either  the  edge  of  the  crown  or  the  edge  of  the  root 
project  beyond  the  common  line  at  any  point,  it  is  to  be  trimmed  down 


BEADY-MADE  CROWNS. 


625 


until  the  line  of  junction  is  uniform.  Any  slight  imperfections  of  con- 
tact are  to  be  remedied  by  means  of  the  carbon-paper  test :  small  pieces 
of  this  material,  large  enough  to  cover  the  face  of  the  root,  are  pressed 


Fig.  787 


Fig.  788. 


to  its  surface  and  perforated  by  the  crown  post.  The  crown  is  now 
pressed  firmly  into  position  and  withdrawn  :  should  there  be  any  breaks 
in  the  black  line,  the  crown  is  dressed  down  at  all  parts  marked  until 
there  is  a  continuous  black  line  at  the  outer  edge  of  the  crown. 

The  crowns  may  be  accurately  adapted  to  the  roots  without  the  use 
of  a  model,  but,  as  it  is  desirable  to  make  a  model  to  serve  as  a  guide  in 
selecting  a  crown  of  the  proper  size  and  form,  the  same  model  may  fur- 
nish a  base  and  guide  for  adapting  it.  The  operation  described  in  reality 
saves  time. 

Fig.  789. 


Prepared  articulating  paper. 


In  fitting  these  crowns  without  a  model  the  canal  is  enlarged  suf- 
ficiently to  receive  the  metallic  post,  the  root  surface  trimmed  to  the 
proper  form  by  means  of  the  root-facers,  and  tlie  crown  is  fitted  as 
follows : 

Dr.  E.  C.  Kir¥s  3Iethod  of  Fitting  a  Logan  Croivn  to  a  Tooth-root. 
— Cut  several  small  pieces,  about  one-quarter  inch  square,  from  a  strip 
of  thin  articulating  paper.  In  the  centre  of  each  punch  a  hole  with  the 
tool  shown  in  the  margin.  Having  prepared  the  root-end,  slip  the  per- 
forated piece  of  articulating  paper  over  the  pin  of  the  Logan  crown  and 

40 


626  ARTIFICIAL  CROWNS. 

press  it  firmly  into  position,  in  contact  with  the  root.  Upon  withdraw- 
ing the  crown  and  removing  the  articulating  paper,  the  points  of  contact 
will  be  found  to  be  marked  black.  Grind  these  off  carefully,  readjust 
on  the  root  as  before,  grind  again,  and  continue  the  operation  of  fitting 
and  grinding  until  the  mark  made  by  the  articulating  paper  on  the  con- 
tact surface  of  the  crown  presents  as  a  uniformly  unbroken  black  ring. 
When  this  has  been  accomplished,  the  crown  will  be  found  to  fit  the 
root-end  with  the  utmost  accuracy.  The  advantages  of  fitting  a  crown 
directly  to  the  root  are,  it  would  seem,  self-evident  from  the  mechanical 
standpoint,  and  involve  besides  the  least  expenditure  of  time.^ 

A  Method  for  Perfectly  Adjusting-  the  Logan  Crown. — "  By  making 
a  considerable  change  in  the  present  form  of  the  Logan  crown,  as  shown 
in  Fig.  790,  1,  A  and  B,  we  have  a  crown  that  can  be  adjusted  in  a  few 
minutes,  and  with  a  degree  of  perfectness  not  yet  obtainable  by  any 
crown  on  the  market,  nor,  within  my  knowledge,  by  any  so  far  sug- 
gested method. 

"The  manner  of  making  the  adjustment  is  certainly  as  simple  as 
could  be  desired. 

"After  preparing  the  canal  for  the  reception  of  the  'Logan  pin,'  select 
a  tooth  in  the  usual  way,  having  regard  to  correct  length,  width,  and 
color,  and  if  care  has  been  exercised  to  select  one  as  near  the  right  length 


as  possible,  it  will  only  be  necessary  to  touch  the  buccal  or  labial  point 
of  the  neck  of  the  crown  a  few  times  with  the  corundum  wheel,  and  the 
proper  length  or  bite  will  be  obtained.  Next  take  a  disk  or  small  piece 
of  thin  platinum  foil,  about  No.  50,  and  push  through  this  the  pin  of 
the  tooth,  carrying  the  disk  up  against  the  porcelain,  as  represented  in 
Fig.  790,  2.  With  a  little  drop  of  Parr's  fluxed  wax  dropped  in  the 
triangular  space,  formed  by  the  backing  and  the  pin,  the  disk  is  held 
securely  in  place,  and  the  platinum  is  trimmed  around  with  small  scissors, 
that  there  may  not  be  any  overlapping.  Now  place  around  the  pin  on 
the  platinum  a  ball  of  Parr's  wax,  stick  the  pin  through  the  second  disk 
of  the  foil,  and  rub  the  platinum  with  a  hot  instrument,  that  the  wax  and 
disk  may  be  sealed  together,  as  shown  in  Fig.  790,  3.  Place  this  in  ice- 
water  to  harden  the  wax,  so  as  to  resist  pressure.  It  is  now  ready  to 
insert,  and  by  pressing  the  tooth  up  until  the  labial  surface  strikes  the 
end  of  the  root,  and  having  the  patient  to  close  the  jaws,  the  correct  bite 
will  be  secured  with  the  opposite  tooth.  It  will  be  found  on  the  removal 
of  the  crown  that  the  platinum  next  the  root  has  been  perfectly  swaged 
to  the  root-end.  This  second  disk  is  now  trimmed  according  to  the  out- 
lines of  the  root.  When  it  is  so  desired,  the  palatine  side  of  the  root 
having  been  left  a  little  high,  or  just  above  the  gum,  the  platinum  can 

^  Dental  Cosmos,  June,  1894. 


BEADY-MADE  CROWNS.  627 

be  split  with  scissors,  lapped,  and  burnished  around  the  exposed  side  of 
'the  root,  to  form  a  partial  band  (Fig.  790,  4). 

"  After  having  dried  the  wax  with  bibulous  paper  and  shaped  up  the 
approximal  sides,  these  sides  are  covered  with  small,  triangular  pieces 
of  platinum  (Fig.  790,  5)  by  lapping  the  platinum  on  the  wax  and  rubbing 
over  it  a  hot  burnisher.  The  crown  is  now  ready  to  invest,  and  the  in- 
vesting mixture  is  poured  on  a  small  piece  of  wire  netting,  which  will 
prevent  its  cracking  during  the  soldering  operation.  The  wax  having 
been  burned  out,  this  triangular  box  is  filled  flush  with  solder  in  the 
usual  way  and  polished.  The  result  is  a  beautiful  and  perfect  crown,  in 
every  respect  the  most  substantial  porcelain  crown  we  have. 

''  I  frequently  make  the  crown  without  using  the  triangular  piece  of 
platinum  to  form  the  box  (Fig.  790,  5),  relying  on  the  investment  to  form 
the  sides.  This  saves  a  little  time ;  but  it  frequently  happens,  unless 
care  has  been  taken  to  make  the  wax  flush,  that  the  approximal  surfaces 
are  not  well  rounded,  and  consequently  do  not  finish  well.  It  is  there- 
fore safer  to  use  the  triangular  pieces  of  platinum  foil  to  form  the  sides 
of  the  box,  as  described,  before  filling  with  solder.  This  plan  is  partic- 
ularly adaptable  to  those  cases  of  fracture  which  have  resulted  in  a  rough 
root-end,  and  where  it  is  often  next  to  impossible  to  get  them  smooth. 

"Where  it  is  convenient  or  if  it  is  desired,  the  triangular  box  can  be 
filled  with  '  body,'  and  baked  in  a  Parker  furnace  from  six  to  eight 
minutes.  This  gives  us  an  all-porcelain  crown  which  fits  perfectly  to 
the  end  of  the  root.  In  this  case  the  first  disk  next  the  porcelain  is  left 
off  entirely."  ^ 

Caution. — The  Logan  crown  contains  a  large  tapered  pin  with  its 
large  end  baked  in  the  tooth,  and  when  heated  to  flow  solder  over  or 
around  it,  care  must  be  taken  that  the  porcelain  is  made  as  hot  as  or 
hotter  than  the  pin,  thus  preventing  uneven  expansion  and  cracking  of 
the  porcelain. 

These  crowns  may  be  adapted  upon  frail  roots,  those  which  demand 
the  supplementary  support  of  a  band  encircling  their  necks.  It  is  a 
matter  of  but  little  practical  moment  whether  the  collar  is  or  is  not 
attached  to  the  crown  :  the  object  sought,  the  protection  of  the  root 
against  longitudinal  fracture,  is  secured  by  banding  the  root  first,  forming 
an  artificial  root  face  by  means  of  metal.  The  root  face  is  trimmed  as 
for  a  collar  crown  ;  the  collar  is  fitted  and  a  cap  soldered  to  it,  the  edge 
of  the  top  being  hidden  at  its  labial  aspect  by  the  gum.  While  the  cap 
is  on  the  root  an  opening  is  made  in  it  considerably  larger  than  the  size 
of  the  crown  post.  A  piece  of  metal  longer  than,  and  slightly  larger  on 
its  sides  than,  a  full  Logan  post  is  greased  with  vaseline  ;  the  root  is 
dried,  zinc  phosphate  is  packed  into  it  for  more  than  half  its  length,  the 
ferrule  partly  filled  by  the  same  mixture  and  pressed  into  position. 
While  the  cement  is  soft  the  metal  wedge  is  thrust  into  the  cement  as 
deep  as  a  Logan  pin,  and  left  until  the  cement  hardens,  when  it  may 
be  readily  withdrawn.  The  crown  is  now  adjusted  to  the  canal  in  the 
cement  and  to  the  edges  of  the  ferrule  top.  The  gold  of  the  cap  may 
be  dressed  away,  together  with  a  portion  of  the  cement,  until  but  a  nar- 
row retaining  rim  of  gold  is  left. 

Logan  crowns  adapted  after  this  manner    are  to  be  cemented  into 

^  Gordon  White,  D.  D.  S.,  Dental  Cosmos,  January,  1893. 


628 


ARTIFICIAL   CROWNS. 


Fig.  791. 


position  as  follows :  An  appropriate  root  clamp  (Ottolengui's)  is  placed 
on  the  root,  and  the  rubber  dam  slipped  over  several  adjoining  teeth  and' 
the  clamp.     The  root  is  well  dried  by  means  of  alcohol  and  the  hot 
blast ;  the  canal  is  wiped  with  a  pellet  or  cone  of  paper  saturated  with 

the  cement  fluid  to  facilitate  the  flow 
of  the  cement.  A  paste  of  cement  is 
made  just  thick  enough  to  be  formed 
into  perfectly  plastic  pellets ;  one  of 
these  is  rolled  into  a  cone,  and  before 
the  latter  bends  by  its  own  weight  it  is 
carried  into  the  canal :  another  is  pressed 
into  the  concavity  in  the  base  of  the 
tooth ;  the  grooves  in  the  post  are  filled ; 
the  crown  is  then  thrust  into  position  and 
pressed  home,  when  the  cement  will  ooze 
from  the  edges,  and  the  joint  should  be 
a  very  thin  line.  The  crown  is  left  un- 
disturbed for  at  least  fifteen  minutes, 
when  the  cement  will  be  found  hard 
enough  to  resist  fracture. 

The  advantages  possessed  by  cement, 
hardness  and  rigidity,  may  be  combined 
with  the  virtue  of  gutta-percha,  insolu- 
bility in  the  fluids  of  the  mouth,  after  the 
following  method  : 

"  First  prepare  and  treat  the  pulp- 
canal  of  the  natural  tooth-root  in  the 
ordinary  way,  the  canal  being  provided 
with  undercuts  or  retaining  points,  and 
fit  the  crown  in  proper  alignment  with 
adjacent  teeth  as  usual.  Fill  the  cup  or 
recess  in  the  neck  of  the  porcelain  crown 
with  gutta-percha,  which  can  best  be  ac- 
complished by  slipping  a  washer  or  per- 
forated disk  of  gutta-percha,  cut  to  cor- 
respond approximately  with  the  size  of 
the  neck  of  the  crown,  over  the  crown- 
pin,  and  after  softening  by  holding  it  in 
the  flame  of  a  burner,  press  the  crown  to 
its  place  upon  the  root.  After  it  has  been 
held  in  position  until  the  gutta-percha  has 
cooled,  remove  the  crown  from  the  root 
and  trim  off"  any  surplus  gutta-percha. 
JSTow  coat  the  end  of  the  root  with  shellac 
varnish,  fill  the  root-canal  with  a  suitable 
amalgam  or  cement,  or,  if  preferred,  pack 
it  with  prepared  gutta-percha  points, 
using  such  an  amount  of  points  as  will 
allow  the  crown-pin  to  enter  the  canal  not 
quite  the  full  length  of  the  pin.  The  opening  for  the  pin  in  the  gutta- 
percha in  the  canal  may  be  made  with  a  heated  instrument  having  a  tapered 


Logan  crown  with  gutta-percha. 


BANDING  LOGAN  CROWNS.  629 

point.  Having  packed  the  crown-recess  with  the  proper  quantity  of 
gutta-percha,  as  above  explained,  place  the  crown  in  position  in  the 
mouth,  heat  the  copper  end  of  a  crown-setter  sufficiently  to  soften  gutta- 
percha, and  place  the  grooved  end  of  the  setter  over  the  crown  with  the 
heated  copper  in  contact  with  the  porcelain.  Hold  the  setter  against 
the  crown  until  the  gutta-percha  becomes  soft,  when  pressure  should  be 
applied  to  the  setter  and  the  crown  with  its  pin  forced  to  its  proper  posi- 
tion. After  the  gutta-percha  becomes  cool,  which  can  be  hastened  by 
dipping  the  crown-setter  in  a  tumbler  of  ice-water  and  holding  it 
against  the  tooth  until  it  is  cold,  cut  off  any  surplus  that  may  be 
squeezed  out  from  between  the  crown  and  root,  with  a  sharp  knife,  and 
then  with  a  hot  tool  smooth  the  edge  of  the  gutta-percha  between  crown 
and  root.  If  the  cutting  is  attempted  while  the  gutta-percha  is  soft,  it 
will  be  dragged  out  of  place. 

"■  The  use  of  gutta-percha  for  packing  the  root-canal,  thus  making 
the  entire  attachment  with  this  material,  possesses  the  advantage  over  the 
use  of  cement  or  amalgam  in  that,  should  the  root  become  abscessed, 
the  crown  may  be  removed  with  a  pair  of  forceps  after  first  heating  it 
with  the  setter,  the  root-canal  treated  until  the  disease  is  cured,  and  the 
crown  reset.  Heating  the  porcelain  crown  when  a  cement  is  used  to  fill 
the  root  around  the  pin  hastens  its  setting.  Do  not  heat  the  crown  if 
amalgam  has  been  used," 

Banding  Logan  Crowns. 

There  are  several  methods  of  banding  the  Logan  crown,  so  that  the 
ferrule  becomes  an  integral  part  of  the  crown.  One  method  of  making 
the  attachment  is  as  follows :  Adapt  the  collar  to  the  root,  and  fit  the  cap 
inside,  not  over  the  band,  soldering  with  22-carat  solder.  Fit  the  Logan 
crown  to  the  ferrule,  perforating  the  latter  for  the  passage  of  the  post, 
which  should  be  grasped  tightly  by  the  cap.  At  the  palatal  side  cut  out 
the  porcelain  for  about  one-sixteenth  of  an  inch,  leaving  only  the  labial 
crescent  of  porcelain  in  contact  with  the  ferrule.  Perforate  a  circle  of 
24-carat  gold  No.  40,  and  pass  over  the  pin  and  burnish  into  the  con- 
cavity in  the  base  of  the  crown.  Perforate  other  pieces  of  thicker  gold 
and  pass  oyer  the  post,  pressing  them  firmly  into  contact  w^th  the  pieces 
previously  placed,  until  the  concavity  is  filled  and  the  last  piece  extends 
to  the  palatal  edge  of  the  crown.  The  pieces  are  covered  by  Parr's 
adhesive  wax ;  the  same  material  is  flowed  over  the  top  of  the  ferrule 
and  the  crown  pressed  into  position  ;  the  crown  and  ferrule  are  placed 
on  the  root  and  adjusted  to  position;  the  wax  is  chilled  by  having  the 
patient  hold  ice-water  in  his  mouth  for  a  few  moments.  An  excavator 
point  is  passed  beneath  the  upper  edge  of  the  collar,  and  it  is  withdrawn 
and  invested.  The  wax  between  the  last,  the  broadest  piece  of  gold, 
and  the  ferrule  top  is  picked  away  and  small  pieces  of  gold  are  used  to 
fill  the  space.  A  liberal  amount  of  18-carat  solder  is  laid  over  the  gold, 
and  the  case  heated  under  the  blowpipe,  directing  the  flame  against  the 
investment  over  the  labial  portion  of  the  crown,  drawing  the  solder 
through  from  the  palatal  side,  adding  more  solder  if  necessary  to  fill  the 
joint  flush. 

Dr.  Townsend's  method  of  attaching  a  band  without  the  top  is 
appended : 


630 


ARTIFICIAL  CROWNS. 


Fig.  792. 


How  to  Band  a  Log-an  Crown. — "  Prepare  the  root  as  usual  for  a 
band  crown,  and  enlarge  the  root-canal  to  receive  the  Logan  pin.  Grind 
a  Logan  crown  to  fit  and  articulate  it.  Construct  a  band  of  No.  30  gold 
(or  of  No.  32  crown-metal,  which  is  better)  wide 
enough  to  project  beyond  the  end  of  the  root,  say 
three  thirty-seconds  of  an  inch.  Cut  a  wooden  peg 
about  an  inch  long,  and  taper  one  end  of  it  to  the 
general  size  and  shape  of  the  pin  in  the  Logan 
crown.  Place  the  band  on  the  root,  insert  the  peg 
in  the  canal,  and  fill  up  the  band  with  Melotte's 
moldine  or  with  stiff  putty,  pressing  it  closely  about 
the  peg.  Remove  all  together,  and,  holding  the 
die  over  the  flame  of  an  alcohol  lamp  to  melt  the 
fusible  metal,  place  them — the  band,  peg,  and  mold- 
ine, in  the  same  relative  positions  they  occupied  in 
the  root — on  the  die,  with  the  pin  in  the  socket, 
and  press  down  until  the  moldine  rests  on  the  sur- 
face of  the  molten  fusible  metal.  Chill ;  in  cooling, 
the  fusible  metal  takes  a  firm  hold  on  the  lower 
edge  of  the  gold  band,  holding  it  securely  in  place 
during  the  remainder  of  the  operation.  Remove 
the  peg  and  the  moldine,  and  with  a  wooden  mal- 
let drive  the  Logan  crown  into  the  band  until  the 
porcelain  rests  upon  the  fusible  metal.  Burnish 
the  band  smoothly  about  the  crown.  When  the 
gold  is  perfectly  adjusted  to  the  porcelain  melt  the 
fusible  metal  to  release  the  band  and  crowm.  If 
the  work  has  been  carefully  done,  the  crown  with 
its  band  will  then  be  ready  to  be  set,  as  the  artic- 
ulation and  fit  will  not  have  been  disturbed." 
Method  of  Mounting  a  Log-an  Crown  with  a  Gold  Cap. — "  With 
regard  to  crowning  teeth,  some  have  no  doubt  met  with  cases  like  the 

following,  where  ordinary  methods  are  not  available  :  Miss  L called 

at  my  office  to  have  a  lower  right  first  bicuspid  crowned.  There  was  a 
considerable  portion  of  the  lingual  part  of  the  crown  standing,  the  buccal 
surface  being  decayed  almost  to  the  gum-margin.  The  coronal  portion 
of  the  pulp  was  calcified,  and  she  objected  to  having  it  destroyed,  nor 
did  I  think  such  a  course  necessary.  Here  an  all-gold  or  even  porcelain- 
faced  crown  would  have  been  too  conspicuous,  so  I  decided  to  apply  a 
Logan  crown, — not,  however,  with  its  ordinary  pin,  but  with  a  cap  and 
collar.  I  trimmed  the  root,  leaving  the  lingual  side  a  little  high,  and 
took  a  model  and  bite  of  it.  A  cap  and  collar  were  made  to  fit  the  root 
accurately  and  tightly.  A  suitable  Logan  crown  was  next  selected,  and 
the  pin  cut  off.  Into  the  countersink  and  around  the  stump  of  the  pin 
I  floioed  pure  gold,  and  then  proceeded  to  fit  the  crown  to  cap  and  bite. 
A  hole  was  next  cut  in  the  cap,  and  enlarged  till  it  nearly  corresponded 
in  size  to  the  gold  base  in  the  countersink  of  the  crown.  Cap  and  crown 
were  now  waxed  together,  and  invested  crown  downward  in  plaster  and 
marble-dust.  This  left  the  interior  of  the  cap  and  band  exposed,  and 
through  the  aperture  in  the  former  all  except  the  edge  of  the  pure  gold 
could  be  seen.     The  wax  was  then  removed  and  the  Avhole  soldered.     A 


1,  socket ;  2,  fusible  metal. 


BANDING  LOGAN  CROWNS. 


631 


slight  groove  was  cut  round  the  remaining  portion  of  the  root  to  assist 
retention,  and  the  crown  was  cemented  in  place."  ^ 

Another  method  is  appended,  the  principle  the  same  as  the  first 
described  : 

Dr.  HoUingsworth's  Method  for  Accurately  Adapting  and 
Mounting  a  Logan  Crown  with  a  Band. — "  Prepare  the  root  in  the 


Fig.  793. 


Fig.  794. 


Fig.  795. 


usual  way  for  banding.  (See  Fig.  793,  front  view,  and  Fig.  794,  side 
view.) 

"  Grind  the  abutting  surface  of  the  crown  to  fit  the  root  under  the 
free  margin  of  the  gum,  along  the  labial  face  only.  (See  Figs.  793,  794, 
a  to  6.) 

"  Cut  the  crown  away  slightly  at  the  lingual  surface,  so  as  to  leave 
a  space  between  it  and  the  end  of  the  root.     (See  Fig,  795,  c.) 

"  Make  a  band  only  wide  enough  to  give  a  good  hold  on  the  root, 
but  not  to  extend  beyond  margin  of  gum  to  fit  the  root  and  trim  off 
even  with  the  end  of  it.  (See  Fig.  795,  d.)  After  fitting  the  band 
properly,  remove  it  and  solder  a  piece  of  pure  gold  plate,  say  about  No. 
34,  on  the  outer  end.  (See  Fig.  795,  e.)  This  can  be  done  quickly  by 
placing  the  plate  in  the  hand  and  pressing  the  band  on  it  with  the 
thumb  for  a  fit,  then  soldering  in  the  flame  of  a  Bunsen  burner.  Punch 
a  small  hole  through  the  plate  to  take  the  pin  in  the  croAvn,  and  replace 


Fig.  796. 


Fig.  797. 


FiG.  7i 


in  position  on  the  root  after  trimming  off  the  exposed  edges.  Now  take 
a  piece  of  thin  pure  gold,  say  No,  34  or  36,  with  ears  as  shown  in  Fig. 
796,/;  punch  a  hole  through  it,  slide  it  over  the  pin  of  the  Logan  crown, 
and  burnish  tightly  to  the  base  of  the  crown.  (See  Fig.  796,  </.)  Next 
^  Dr.  Gird  wood,  Dental  Cosmos,  January,  1894. 


632  ARTIFICIAL  CROWNS. 

warm  the  pin  and  place  a  sufficient  quantity  of  Parr's  fluxed  wax  around 
it  as  shown  by  dotted  lines,  Fig.  796,  Replace  the  Logan  crown  on  the 
root  (with  the  cap  in  position),  force  home  until  the  labial  edges  of  root 
and  crown  meet,  obtain  the  proper  alignment,  and  cool  and  harden  the 
wax  by  using  a  napkin  with  ice-water.  Then  remove  the  crown  and  cap 
together,  held  in  proper  relative  position  by  the  wax.  (See  Fig.  797.) 
Trim  off  the  surplus  wax  and  invest.  (See  Fig.  798.)  Remove  all  the 
wax  possible  between  the  crown  and  the  band,  and  flow  20-carat  gold 
solder  into  the  space.  The  wax  which  will  necessarily  remain,  being 
fluxed,  will  carry  the  solder  into  every  crevice  and  give  the  crown  great 
strength.  Finish  the  band  and  the  soldered  edges,  and  the  result  will  be 
a  strong  and  perfectly  aligned  crown. 

Brown  Cro-wn. — This  crown  is  made  with  a  curved  base,  reducing 
the  risk  of  fracture  of  the  crown  itself.  The  canal  is  reamed  for  the 
reception  of  the  post.  It  is  very  difficult  to  adapt  this  crown 
Fig.  799.  with  great  accuracy.  The  root  is  more  readily  formed  to 
receive  the  crown  than  is  the  crown  to  fit  the  root  face.  A 
crown  of  the  exact  size,  shape,  and  color  of  its  fellow  is 
selected.  A  Willard  countersinking  bur  (Fig.  799)  is  em- 
ployed in  cutting  away  the  points  of  contact  with  the  crown 
base.  If  it  be  necessary  to  trim  the  crown  base  itself,  it  is 
most  readily  done  by  means  of  a  diamond  disk  having  a  safe 
edge.  If  the  canal  have  been  reamed  out  so  that  the  post  fits 
the  canal  snugly,  these  crowns  may  be  set  with  gutta-percha. 

This  variety  of  crown,  owing  to  its  great  strength,  is  well 
adapted  as  an  abutment  crown  of  the  all-porcelain  bridge, 
crown  and  bridge  both  designed  by  Dr.  E.  Parmley  Brown. 
The  New  Richraond  Crown.  —  The   description   of  this 
special  crown  and  its  field  of  application  are  thus  set  forth  by 
W.  Storer  How,  D.  D.  S.,  Philadelphia,  Pa.  : 

"  The  usual  preliminary  treatment  of  the  natural  tooth-root  and  the 
filling  of  the  apical  fourth  part  of  the  pulp-canal  are  predicated  of  all 
the  cases  which  will  here  be  described  and  illustrated,  in  exemplifica- 
tion of  the  preferred  mode  of  mounting  the  new  porcelain  tooth-crown 
invented  by  Dr.  C.  M.  Richmond. 

"A  superior  left  central  incisor  root  will  serve  as  a  typical  case,  and  its 
projecting  end  is  to  be  shaped  as  seen  in  Figs.  800  and  801.  This  can  be 
rapidly  done  with  a  narrow,  safe-sided  flat  or  square  file,  the  angles  of 
the  slopes  being  such  that  the  gum  on  the  labial  and  palatal  aspects  will 
not  interfere  with  nor  be  disturbed  by  the  operator  in  this  preliminary 
work,  for  the  root-end  is  not  at  this  time  to  be  cut  quite  down  to  the 
gum.  An  Ottolengui  root-reamer  No.  2  is  then  employed  to  bore  out 
the  root  to  receive  the  crown-post,  which  is  of  the  same  size  and  shape 
as  the  Logan  crown-post  for  a  central  incisor.  Fig.  802  shows  in  sec- 
tion the  relation  of  the  reamer  to  the  root.  The  new  Richmond  crown 
(Fig.  803)  is  then  put  on  the  root  (see  Fig.  804),  and  its  position  rela- 
tive to  the  adjacent  and  occluding  teeth  noted.  If  the  cutting  edge  of 
the  crown  is  to  be  brought  out  for  alignment  with  its  neighbors,  the  root 
can  be  drilled  a  little  deeper  and  the  reamer  pressed  outward  as  it  revolves 
to  cut  the  labial  wall  of  the  cavity.  The  palatal  root-slope  must  then  be 
tiled  to  make  the  V  correspond  to  the  changed  inclination  of  the  crown. 


BANDING  LOGAN  CROWNS. 


63-^ 


"  Thus,  by  alternate  trial  and  reaming  and  filing  the  crown  may  be 
fitted  to  the  root  and  adjusted  in  its  relations  until  the  post  has  a  close, 
solid  bearing  against  the  labial  and  palatal  walls  of  the  enlarged  pulp- 
cavity,  and  the  crown-slopes  separated  from  the  root-slopes  by  the  thickness 
of  a  sheet  of  heavy  writing-paper.  This  space  can  be  accurately  gauged 
and  the  root-slopes  conformed  to  the  crown-slopes  by  warming  the  crown 
and  putting  on  its  slopes  a  little  gutta-percha,  so  that  an  impression  of 
the  root-end  may  be  taken,  and  the  root-slopes  dressed  with  a  file  until 
the  film  of  gutta-percha  proves  to  be  of  equal  thinness  on  both  slopes. 
After  thus  completing  the  adjustment,  with  due  attention  to  the  align- 
ment and  occlusion,  the  crown  and  the  root  are  to  be  dried  as  thoroughly 
as  possible, 

"  To  do  this  effectively  in  the  root  it  should  first  be  swabbed  and 
washed  out  with  absolute  alcohol,  and  then  continuously  flooded  with 


Fig.  800. 


Fig.  801. 


Fig.  802. 


warm  air,  until  the  root  is  not  merely  dry,  but  dried  throughout  as  far 
as  possible,  and  made  so  Avarm  as  to  render  the  patient  conscious  of  its 
heat.    A  little  gutta-percha  is  then  put  on  the  sides  of  the  post  and  over 


Fig.  803. 


Fig.  804. 


Fig.  805. 


Fig.  806. 


the  slopes  of  the  crown,  which  is  then  pushed  into  place,  the  exuding 
gutta-percha  cut  away,  and  the  joint  smoothed  with  a  warm  burnisher. 
The  film  of  gutta-percha  should  be  very  thin.  The  crown  and  root  may 
be  quickly  cooled  by  the  use  of  the  syringe  with  cold  water,  and  the 
patient  then  enjoined  to  let  the  crown  rest  for  a  few  hours  in  order  that 
the  gutta-percha  may  become  quite  set.  Fig.  805  shows  the  completed 
crown. 

"  Dr.  Richmond  usually  takes  a  thin,  perforated  disk  of  gutta-percha, 
pushes  the  post  through  it,  warms  the  crown,  presses  it  into  place,  and 
when  cooled  removes  the  crown,  and  with  a  sharp  knife  trims  away  the 
gutta-percha  close  to  the  crown-neck.  He  then  warms  the  crown,  puts  a 
very  little  oxyphosphate  cement  on  the  post,  and  presses  the  crown  home. 


634  ARTIFICIAL   CROWNS. 

"  The  obvious  advantages  of  the  device  are — the  readiness  with  which 
the  slopes  of  the  root-end  may  be  shaped  with  a  file ;  the  facility  with 
which  these  slopes  may  be  given  any  angle  to  set  the  crown  out  or  in  at 


Fig.  808.  Fig.  809. 


the  base  or  at  the  cutting  edge,  or  to  give  it  a  twist  on  its  axis ;  the 
certainty  that,  once  adjusted,  the  final  setting  will  exactly  reproduce  the 
adjustment ;  the  assurance  that  in  use  the  crown  will  not  be  turned  on 
its  axis — a  most  common  cause  of  the  loosening  of  artificial  crowns ;  the 
firmness  of  its  resistance  to  outward  thrust  in  the  act  of  biting.  This 
fact  is  made  apparent  by  Fig.  806,  wherein  it  will  be  seen  that  in  an 
outward  movement  the  crown  B  must  rock  upon  ^  as  a  pivot,  while  the 
dotted  line  D  shows  how  the  crown-slope  is  resisted  by  the  root-slope, 
which  extends  so  far  toward  the  incisive  edge  that  a  much  firmer  sup- 
port is  given  to  the  crown  than  if  the  resistance  should  be,  as  it  usually 
is,  on  the  line  of  the  gingival  margin  C. 

''  The  cases  for  which  the  new  crown  seems  specially  adapted  are 
such  as  have  some  considerable  portion  of  the  natural  crown  remaining, 
and  for  these  it  would  seem  that  no  better  artificial  substitute  has  yet 
been  made  accessible  to  the  profession. 

"  For  roots  that  have  become  wasted  below  the  gum-surface  the  new 
crown  is  not  suitable,  except  in  such  cases  as  are  decayed  under  the 
labial  or  palatal  gum-margin  only,  but  have  yet  projecting  the  approxi- 
mal  portions  of  the  crown.     (See  Fig.  807.) 

"  The  sectional  view  (Fig.  808)  and  the  perspective  plan  views  (Fig. 
809)  illustrate  the  manner  of  mounting  these  crowns  on  this  class  of 
roots.     The  finished  crown  appears  as  in  Fig.  809. 

"  The  successive  steps  of  the  process  must  in  every  instance  be  taken 
Avith  prudence,  skill,  and  judgment,  while  carefully  considering  every 
circumstance  and  detail  as  progress  is  being  made  in  the  operation.  For 
example,  in  the  fitting  of  the  crown  to  the  root  it  will  require  nice  obser- 
vation and  discrimination  to  determine  whether  the  crown  is  resting  on 
one  or  both  of  the  root-slopes  or  on  the  post-slopes  in  the  reamed  canal. 
Emphasis  on  the  necessity  of  due  attention  to  all  the  considerations  con- 
nected with  the  adaptations  and  manipulations  of  these  crowns  appears 
all  the  more  requisite  when  one  observes  the  avidity  with  which  thought- 
less enthusiasts  take  hold  upon  a  new  device." 

Removable  Crowns. 

Types  of  these  crowns  were  formerly  made  to  admit  of  easy  removal 
for  treatment  of  diseased  alveoli.  They  are  constructed  as  the  post  and 
plate  crown,  but  instead  of  being  fastened  in  the  pulp-canal,  their  posts 


REMOVABLE  CROWNS.  635 

are  slipped  into  a  close-fitting  tube  which  has  been  fixed  in  the  root  at  a 
previous  operation.  Another  purpose  served  by  them  was  to  prevent 
turning  of  the  post  in  the  canal  and  thus  altering  the  position  of  the 
crown,  the  tube  being  made  square  or  triangular.  The  original  method 
consisted  in  first  forming  the  tube.  A  piece  of  triangular  wire  of  No. 
16  gauge  was  covered  by  thin  platinum  of  about  No.  33  or  No.  34,  the 
platinum  burnished  closely  to  the  wire.  The  wire  withdrawn,  the  line 
of  junction  on  the  plate  was  touched  by  borax  and  soldered  with  pure 
gold.  The  canal  of  the  root  was  reamed  for  two-thirds  its  length  and 
the  length  measured  on  the  tube.  The  wire  was  thrust  through  the  tube 
and  projected  for  about  one-eighth  of  an  inch  at  its  end,  and  the  tube 
sawn  off  to  the  length  marked,  cutting  through  wire  and  tube.  In  the 
apex  of  the  root  a  strand  of  gilling  twine  or  a  twist  of  oiled  cotton  was 
placed.  The  tube  and  wire  were  then  inserted  in  the  root,  the  tube  flush 
with  the  prepared  root-face,  the  wire  projecting.  Amalgam  was  packed 
about  the  tube  by  means  of  slender  instruments  until  the  filling  was  flush 
with  the  root  surface ;  some  operators  packed  gold  instead  of  amalgam 
about  the  tube.  The  wire  was  withdrawn,  the  thread  caught  on  the  end 
of  a  broach,  and  it  was  removed.  The  post  and  plate  crown  w^as  then 
made,  using  the  triangular  wire  for  the  post.  Round  and  square  tubes 
and  wires  were  also  employed.  This  device  forms  the  principle  of  con- 
struction of  one  of  the  present  abutment  crowns  of  a  removable  bridge 
piece. 

A  removable  crown,  devised  by  Dr.  C  M.  Richmond,  is  employed  as 
an  abutment  crown  for  removable  bridges.  The  root  is  trimmed  and  the 
pulp-canal  enlarged  for  about  half  its  depth  to  receive  a  post  slightly 
larger  than  No.  16  gauge  (Fig.  810).  A  ferrule 
is  made  to  fit  the  prepared  root,  and  an  opening  Fig.  810. 

made  through  its  top,  uncovering  the  canal  en- 
trance. A  thin  piece  of  iridio-platinum  plate  is 
bent  into  a  cylinder  to  enclose  tightly  a  No.  16 
wire.  This  cylinder  is  soldered.  The  wire  is 
placed  in  the  cylinder,  and  the  pieces  are  thrust 
through  the  opening  in  the  cap  into  the  canal. 
Ferrule   and  cylinder  are  united  by  means  of 

adhesive  wax,  withdrawn,  and  invested.  The  wire  is  removed  from  the 
cylinder,  the  opening  of  which  is  filled  with  whiting.  The  cylinder 
is  attached  to  the  ferrule  by  means  of  solder.  It  is  then  boiled  in 
pickle,  smoothed,  and  polished.  The  wire  post  is  greased,  placed  in  the 
tube,  and  the  piece  is  cemented  to  the  root.  The  greased  wire  is  with- 
drawn, and  serves  as  the  post  of  a  plate  and  post  crown,  which  is  then 
constructed.  To  ensure  tightness  of  the  post  in  its  socket  the  end  of  the 
wire  is  to  be  slotted  for  about  one-eighth  of  an  inch  or  more  by  means 
of  a  very  fine  saw-blade.  The  leaflets  thus  made  are  slightly  separated, 
so  that  some  pressure  is  necessary  to  force  the  post  into  its  socket. 

The  Genese  Crown. — This  crown  contains  a  small  platinum  cup 
burnt  in  the  porcelain,  into  which  the  post  which  enters  the  root-canal  is 
soldered.  The  crown  is  then  to  be  adjusted  to  the  root  and  fastened  to 
it  by  oxyphosphate  cement  in  the  usual  way.  These  crowns,  like  those 
of  Bonwill  and  Foster,  may  be  replaced,  should  one  of  them  break,  with- 
out removing  the  post. 


636 


ARTIFICIAL  CROWNS. 


Facings  for  Bridg-e-work. — Dr.  D.  Genese  lias  introduced  a  thin 
porcelain  facing  for  bridge- work,  the  inner  surface  of  which  is  lined 
with  thin  platinum  imbedded  in  the  porcelain  by  means  of  a  fold  in  the 
thin  metal.  The  platinum  serves  the  purpose  of  a  backing,  and  the 
teeth  may  readily  be  soldered  to  the  framework  of  the  bridge  without 
other  preparation  than  the  usual  fitting. 

Cro"wns  with  Removable  Pins. — This  form  of  crown  has  been  intro- 
duced for  the  purpose  of  having  a  readily  detachable  pin  which  is  capable 
Fig  811        ^^  ^^^7  ^^^^  permanent  fastening.     It  consists,  as  shown  by 
Fig.  811,  of  a  porcelain  crown  having  a  threaded  socket,  I, 
to  which  is  fitted  a  corresponding  threaded  silver  pin,  II. 
The  advantages   claimed    for   it  are   that  the   pin    may  be 
detached,  so  that  the  fitting  of  the  crown  to  the  root  may 
be   accomplished   with    greater   convenience,   and   that    the 
pin  may  be  bent  in  adjusting  it  to  the  root  while  detached 
from  the  crown,  thus  avoiding  danger  of  fracturing  the  porcelain. 


Fig.  812. 


Fig.  813. 


The  porcelain  facing  is  to  be  adapted  to  the  root  face  by  grinding. 
A  layer  of  wax  is  then  placed  over  the  root  and  the  crown  pressed  into 
it,  indicating  the  exact  site  to  be  occupied  by  the  threaded  screw.  The 
root  is  then  reamed  at  the  point  indicated  until  it  readily  admits  the 
post  and  is  of  sufficient  depth  to  serve  to  retain  the  post  securely,  the 
crown  screwed  on  the  thread,  and  the  post  is  fastened  in  the  canal  as  for 
any  post  crown. 

The  HoUing-sworth  System  of  Crown-  and  Bridge-work. — A 
system  which  affords  greater  range  of  ready  application  than  any  of 
its  predecessors  is  that  known  as  the  "  Hollingsworth."  Its  claims 
and  description  are  thus  given  by  its  inventor : 

"  Accuracy  of  method,  simplicity  of  procedure,  and  beauty  of  result 
are  essential  to  any  system  of  making  crowns  or  building  bridges  which 
shall  bring  the  successful  prosecution  of  this  desirable  branch  of  practice 
within  the  reach  of  the  great  majority  of  dentists. 

"  The  Hollingsworth  system  has  been  before  the  profession  more  than 
two  years,  and  it  has  made  many  men  crown-  and  bridge-workers  who 
before  its  advent  sent  their  patients  to  specialists.  Any  dentist  of  aver- 
age attainments  can  work  it  successfully. 

"  This  system  supplies,  in  the  first  place,  a  variety  of  forms  for  the 
various  teeth  great  enough  to  cover  almost  any  case,  and  for  the  rare 
cases  which  cannot  be  suited  direct  it  affords  a  ready  means  of  making 
the  exact  form  required.  There  are  in  the  set  two  hundred  and  four 
forms  of  cusps  and  thirty-six  of  facings  for  bicuspids  and  molars,  and 
forty  forms  for  incisors  and  cuspids.  These  last  give  both  the  labial  and 
lingual  faces.     All  the  forms  are  exact  facsimiles  from  nature,  selected 


REMOVABLE  CROWNS. 

Fig.  814. 


637 


638 


ARTIFICIAL  CROWNS. 


with  great  care  to  cover  the  widest  range  possible.  They  are  made  of 
metal,  and  are  used  as  patterns  from  which  to  make  dies  or  moulds,  as 
may  be  required,  for  the  swaging  of  gold  cusps  or  crowns.  There  is 
therefore  no  wear  upon  them,  and  they  retain  their  shapes  and  sizes  un- 
altered. 

"  The  outfit  for  working  these  forms  consists  of  a  moulding  plate, 
three  rubber  rings,  a  sheet  of  asbestos  10  by  7  inches,  a  carbon  stick  for 
use  in  casting,  and  a  box  of  HoUings worth's  annealed  copper  strips  for 
measuring  roots. 

"  This  system  permits  cusps  to  be  made  either  hollow  or  solid.  Scrap 
gold  can  be  used  for  casting  solid  cusps,  and  porcelain  facings  can  be 
quickly  inserted  in  crowns  without  investing ;  but  perhaps  its  most  im- 
portant advantage  is  the  exactness  with  which  the  fit  and  articulation 
of  bridges  are  obtained  and  maintained." 

Directions  to  Make  a  Gold-croion  Bicuspid  or  Molar. — Make  a 
band  to  fit  the  root  in  the  ordinary  way.  Place  the  band  in  the  mouth 
(see  Fig.  815),  and  cut  off  on  a  line  where  the  adjoining  teeth  begin 
to  turn  to  form  the  cusp  (see  c.  Fig.  815).  Place  a  small  piece  of 
wax  inside  the  band  to  assist  in  holding  the  cusp-button,  which  should  be 
selected  to  fit  the  circumference  of  the  band,  to  articulate  properly,  and 


Fig.  815. 


Fig.  817. 


Fig.  816. 


Fig.  818. 


Fig.  820. 


Fig.  821. 


Fig.  822. 


to  correspond  in  shape  with  the  other  teeth  (see  6,  Fig.  815).     Remove 
the  button  and  place  it  on  the  moulding-plate  with  the  grinding  surface 


REMOVABLE  CROWNS. 


639 


up  (see  Fig.  816).  Place  the  small  rubber  ring  d  around  it,  with  the 
button  as  near  the  centre  as  possible,  and  pour  in  a  sufficient  quantity  of 
Melotte's  metal  to  nearly  fill  the  ring  (Fig.  817).  Start  to  pour  the 
metal  directly  on  top  of  the  cusp,  otherwise  the  flow  of  metal  may  force 
the  cusp  to  one  side  and  make  an  imperfect  die.  As  soon  as  the  metal 
sets,  chill  the  surface  by  dipping  in  water  for  a  moment,  and  then  remove 
the  rubber  ring.  When  the  heat  begins  to  return  to  the  surface,  a 
quick  rap  of  the  die  on  the  bench  will  cause  the  cusp-button  to  drop  out 
and  leave  the  mould  ready  to  form  the  gold  cusp.  Now  take  a  piece  of 
lead  (Figs.  818  and  819)  and  with  a  hammer  drive  into  the  Melotte-metal 
die  (Fig.  820)  to  form  the  counter-die. 

Anneal  the  gold  plate,  and  start  the  swaging  process  by  coaxing  the 
plate  into  the  die  by  hand-pressure  (Fig.  820),  using  a  piece  of  wood, 
which  makes  a  depression  for  the  lead  counter-die  to  rest  in.  Then 
place  the  counter-die  on  the  gold  plate  (Fig.  821)  and  drive  to  a 
partial  fit.  Remove  the  partially  formed  cusp,  pickle  it  to  remove 
traces  of  lead,  and  again  anneal  it.  Place  the  counter-die  on  the  die 
without  the  gold  plate,  and  drive  it  in  with  a  smart 
blow ;  this  will  resharpen  all  the  lines  of  the 
counter-die.  Next  replace  the  partly  formed  gold 
cusp  in  the  die,  and  again  drive  the  counter-die  into 
it  for  a  perfect  fit.  Again  pickle  the  cusp,  and  pro- 
ceed to  cut  the  surplus  metal  from  it  with  shears 
(Fig.  822),  filling  up  the  edges  when  necessary, 
and  rub  down  the  under  surface  on  a  smooth  file 
until  its  fits  the  band  made  for  it  (Fig.  815). 
Wire  the  cusp  and  crown  together  (Fig.  823),  place 


Fig.  823. 


Fig.  824. 


Fig.  825. 


flux  and  solder  in  the  cap,  and  hold  over  a  lamp  until  soldered.     Then 
finish  in  the  usual  way. 

Note. — If  the  forms  of  cusp-buttons  do  not  afford  one  which  articu- 
lates perfectly,  the  difficulty  is  easily  remedied  by  taking  the  button  which 
most  nearly  answers,  and  building  up  the  cusps  with  Melotte's  moldine 
(Fig.  824).  If  necessary  to  make  an  absolutely  perfect  articulation, 
and  the  forms  as  supplied  do  not  permit  of  it,  select  a  cusp  that  will 
otherwise  suit  the  case,  set  it  on  the  band  on  the  crown,  cover  the  face 
of  the  cusp  with  moldine,  coating  the  surface  with  collodion  to  prevent 
the  saliva  from  crumbling  it,  and  direct  the  patient  to  bite  upon  it,  or,  if 
a  perfect  plaster  model  has  been  made,  articulate  the  opposing  teeth  with 
the  cusp  placed  on  the  band,  omitting  the  coating  with  collodion.  Remove 
the  cusp  with  the  moldine,  trim  off  the  surplus,  and  proceed  to  cast 
as  shown  in  Fig.  817.     If  a  band  is  accidentally  cut  too  short,  it  can 


640 


ARTIFICIAL   CROWNS. 


still  be  utilized.     Place  moldine  upon  the  moulding-plate,  put  the  cusp- 
button  upon  it,  press  down  and  adjust  to  make  up  the  deficiency  of  the 


Fig.  826. 


FtG.  827. 


J 


band,  cutting  away  the  surplus  moldine.  This  will  of  course  throw  the 
soldering  line  a  little  farther  up  on  the  crown  (Fig.  825). 

To  Make  Solid  Gold  Cusps. — Scrap  gold  can  be  utilized  for  making 
a  solid  gold  cusp  by  casting  in  asbestos  by  the  following  method : 

After  selecting  the  desired  cusp-button,  instead  of  making  a  mould  in 
Melotte's  metal,  as  before  described,  take  a  piece  of  asbestos  board  about 
one  inch  square  and  one-fourth  inch  thick,  moisten  it,  and  with  a  ham- 
mer drive  the  cusp-button  into  it  flush  with  the  surface  of  the  button. 
(See  Fig.  826.)  Remove  the  button,  and  dry  the  asbestos  in  a  flame 
(Fig.  826).  When  perfectly  dry,  place  a  sufficient  quantity  of  gold 
scraps  in  the  die  made  in  the  asbestos,  and  direct  the  blowpipe  flame 
upon  it  until  melted,  inclining  the  carbon  stick,  as  shown,  against  the 
die  for  the  double  purpose  of  confining  the  heat  and  warming  up  the 
carbon  stick.  When  the  gold  is  fused  into  a  button,  press  it  into  the  die 
with  the  carbon  stick  (Fig.  827).  Avoid  the  use  of  flux  when  working 
with  asbestos. 

To  build  up  a  cusp  to  make  a  perfect  articulation  in  this  manner, 
sealing-wax  must  be  used  instead  of  moldine,  as  in  the  method  of  swag- 
ing the  cusp.  Warm  the  button  before  applying  the  wax,  and  with  a 
warm  instrument  shape  the  cusp  as  desired. 

To  Make  Gold  Crowns  ( Centrals,  Laterals,  and  Cuspids). — Select  from 


Fig.  829. 


Fig.  831. 


Fig.  828. 


,'B 


the  forty  difl'erent  forms  in  the  set  that  which  is  most  suitable  to  the  case 
in  hand  (Fig.  828).     (The  forms  are  in  pairs,  showing  labial  and  lingual 


REMOVABLE  CROWNS. 


641 


surfaces.)  Take  the  measurement  of  the  root  to  be  crowned  with  one 
of  the  annealed  copper  strips,  binding  the  strip  around  the  tooth  with 
pliers  and  pinching  the  joint  firmly  together.  Trim  off  the  surplus 
ends,  and  cut  the  measure  (Fig.  829,  A)  through  the  centre  (Fig.  829,  B), 
then  bend  the  respective  halves  over  the  lingual  and  labial  forms  selected, 
at  the  necks,  with  the  cut  ends  of  the  strips  resting  on  the  flat  of  the 
plate  (Fig.  830).  If  the  measure  is  larger  than  the  form  selected,  build 
the  latter  up  with  moldine  until  the  space  between  the  form  and  strip  is 
filled  (Fig.  830,  B).  Avoid  getting  moldine  on  the  approximal  surface. 
Remove  the  strips,  dry  out  the  moldine  by  passing  through  a  flame  a  few 
times,  then  place  the  form  on  the  moulding  plate  with  a  rubber  ring 
around  it.     Pour  Melotte's  metal  into  the  ring  as  in  forming  the  molar 

or  bicuspid  cusp,  which  makes  a  die 
of  the  two  sections,  lingual  and  labial. 
Make  a  lead  counter-die  and  proceed 
as  directed  in  the  making  of  a  molar 
cusp,  swaging  the  sections  separately 
(Fig.  831).  Trim  off  the  surplus  plate 
(Fig.  832),  and  square  the  opposing 
edges  of  the  two  sections  by  rubbing 
them  over  a  dead  smooth  file.  Bind 
the  two  sections  together  with  wire 
with  sufficient  solder  and  flux  inside 
(Fig.  833  and  Fig.  834),  and  proceed 
as    in    soldering    an    ordinary    band.. 

Fig.  835. 


Fig,  832. 


Fig.  834. 


With  a  small  mechanical  saw  cut  off  the  upper  portion  where  the  tooth 
begins  to  slope  back  (about  the  dotted  lines  in  Fig.  834).  This  leaves 
the  crown  as  shown  in  Fig.  835,  approximal  and  labial  views.  Drive 
on  the  root.  If  too  small,  place  on  the  horn  of  an  anvil  and  enlarge  by 
hammering ;  if  too  large,  band  the  root  in  the  same  manner  as  for  a 
Richmond  crown,  grinding  the  tooth  to  fit. 

To  Insert  a  Porcelain  Facing. — Make  the  gold  crown  as  described. 
Select  a  porcelain  facing  suitable  for  the  case  (Fig.  836).  Place  the 
crown  on  the  root  in  the  mouth,  and  with  an  excavator  mark  on  the  face 
where  the  porcelain  is  to  appear.  Remove  the  crown  and  saw  out,  so 
that  the  facing  will  fit  looselv.  With  a  knife  bevel  the  inner  edge  or 
seat  for  the  facing  (Fig.  837)."  Grind  the  facing  to  fit  (Fig.  838).  Back 
up  the  facing  with  No.  34  or  36  gauge  pure  gold,  punching  holes  in  the 
backing  for  pins,  annealing  as  required  to  readily  conform  it  to  the  tooth 
(Fig.  839  and  Fig.  840).  With  a  sharp  knife  cut  a  barb  on  each  side 
of  the  pins  in  the  facing,  and  press  the  barbs  against  the  backing  (Fig. 
841),  to  keep  the  backing  in  place.  Burnish  down  the  edges  well,  being 
careful  not  to  let  the  backing  overlap  the  facing. 

Place  the  facing  in  the  space  prepared  for  it  in  the  crown  (Fig,  842), 

41 


642 


ARTIFICIAL   CROWNS. 


and  bind  the  two  together  (not  too  tight)  with  wire,  wrapping  the  wire 
directly  over  the  facing  with  asbestos  to  prevent  discoloration  of  the 
porcelain.  Flux  and  solder  by  holding  over  a  lamp  as  in  the  case  of  a 
band  (Fig.  843).     Then  finish  in  the  usual  way. 

If  it  is  desired  to  use  a  platinum  pin  for  anchorage — as,  for  instance, 
a  Logan  pin — bend  the  pins  in  the  facing  sufficiently  to  clamp  the  an- 


FiG.  836. 


Fig.  837. 


Fig.  838. 


Fig.  843. 


Fig.  840.  Fig.  841. 


Fig.  842. 


Fig.  844. 


chorage  pin,  and  insert  the  pin  through  the  gold  crown  (Fig.  844),  finish- 
ing as  before  described.     Fig.  845  shows  a  finished  crown  so  made. 

Annealed  Copper  Strips. — These  strips  will  be  found  more  desirable 
and  practical  than  the  ordinary  binding-wire  for  taking  measurements 
of  roots,  especially  of  badly-decayed  teeth.  To  use  them,  the  strip  is 
passed  around  the  tooth,  and  the  joint  pinched  firmly  with  a  pair  of 
pliers.  Where  the  decay  runs  under  the  gum,  tack  the  ends  of  the  strip 
together  with  soft  solder,  and  with  an  excavator  carry  it  well  up  under 
the  gum. 

By  the  Hollingsworth  system  the  following  operations  are  performed 
with  great  ease  and  accuracy  :  Gold  crowns,  bicuspids  and  molars ; 
gold  crowns,  incisors  and  cuspids ;  solid  gold  cusps ;  grinding  surface 
of  a  bridge  in  one  continuous  piece ;  porcelain  facings ;  facings  for 
making  an  all-gold  bridge. 

The  large  cut  (Fig.  814)  shows  the  cusp  and  crown  forms  in  a  fold- 
ing case  as  they  are  put  up  for  sale.  In  the  upper  half  of  the  case 
there  are  two  hundred  and  forty  cusp  forms  and  facings  for  bicuspids 
and  molars ;  in  the  lower  half  there  are  forty  forms  for  incisor  and 
cuspid  crowns.  From  this  great  number  patterns  can  readily  be  selected 
that  will  perfectly  articulate  with  the  opposing  teeth. 

A  (Fig.  814)  is  the  polished  plate  upon  whic^h  the  dies  are  made. 

jB  is  a  carbon  rod  for  pressing  the  melted  metal  into  the  asbestos 
mould. 


REPAIRING    OF  CROWNS.  643 

G  is  part  of  the  asbestos  sheet,  7  by  10  inches,  in  which  dies  are 
formed  for  casting  solid  gold  cusps. 

T)  is  a  box  of  annealed  copper  strips  for  taking  the  measure  of  the 
root  to  be  crowned. 

E  and  F  are  rubber  rings  in  which  the  die  is  made  from  Melotte's 
metal. 

Numerous  other  systems  have  been  devised  to  facilitate  the  operations 
of  crown-  and  bridge-work,  but  all  of  them  have  either  such  limitations 
as  to  accuracy  or  insufficiency  of  application  that  the  description  of  them 
would  needlessly  overload  these  pages. 

Repairing  of  Crowns. 

The  chief  accident  befalling  artificial  crowns  is  fracture  of  their 
porcelain  facings.  It  is  unusual  for  those  composed  wholly  of  metal  to 
require  repair ;  occasionally,  if  made  of  too  thin  metal,  these  crowns  may 
wear  through  and  expose  the  cement. 

It  may  be  found  necessary  to  remove  a  barrel  croAvn  to  gain  access 
to  the  root-canals  in  order  to  sterilize  these  canals  should  sterilization 
have  been  incomplete  before  the  crown  was  set  or  in  the  event  of  a  pulp 
dying  and  decomposing  subsequent  to  the  setting  of  the  crown.  When 
the  crown  has  been  properly  fitted  and  attached,  it  will  be  found,  as  a 
rule,  that  it  is  necessary  to  split  the  barrel  to  enable  the  operator  to  detach 
the  crown.  A  sharp  hatchet  excavator  is  drawn  from  the  cervical  edge 
to  the  masticating  surface  of  the  crown,  making  a  groove  of  increasing 
depth  until  the  division  of  the  barrel  is  complete,  when  the  edges  of  the 
flaps  are  bent  away  from  one  another ;  a  fine  explorer  is  passed  beneath 
the  cap  as  far  as  possible  and  the  cement  dislodged  piecemeal.  A  broad- 
edged  excavator  is  then  placed  above  the  edge  of  the  collar  and  traction 
exerted  at  all  points  until  the  barrel  loosens. 

The  crown  is  now  boiled  in  strong  nitric  acid  to  dissolve  the  rem- 
nants of  cement  attached  to  it.  It  is  then  readjusted  to  the  tooth, 
the  cut  edges  brought  into  apposition,  and  removed  from  the  root. 
Should  it  be  necessary  to  repair  thin  areas  or  spaces  where  the  crown  is 
worn  through,  a  piece  of  platinum  No.  36  is  pressed  against  the  break 
from  the  inside ;  an  ample  amount  of  flux  is  flowed  over  the  surface,  and 
sufficient  solder  (16-carat)  placed  in  the  cap  and  fused  over  a  Bunsen 
flame. 

To  repair  the  line  of  division,  a  strip  of  thin  platinum  about  one-six- 
teenth of  an  inch  wide  is  covered  with  fluxed  solder  filings  and  pressed 
against  the  break  in  the  inside  of  the  barrel.  The  crown  is  now  invested, 
fully  exposing  the  line  to  be  soldered,  which  is  covered  by  borax  and  a 
small  piece  of  solder  laid  at  each  end  of  the  line.  The  crown  is  now 
heated  and  soldered. 

To  remove  collar  crowns  having  their  porcelain  facings  broken  away, 
it  is  advisable  to  first  groove  the  backing  from  its  upper  edge,  making 
two  slots  large  enough  to  permit  the  slipping  of  the  pins  of  the  new 
facing  into  them.  A  fissure  bur  is  passed  through  the  base  of  the  stay 
and  top  of  the  ferrule,  severing  the  attachment  of  the  post ;  an  old  exca- 
vator is  passed  beneath  the  cap,  its  angle  resting  upon  the  face  of  the 
root,  and  the  endeavor  made  to  pry  oif  the  ferrule,  for,  if  possible, 
the   ferrule  should  be  removed  without    splitting.       The  stay  may  be 


644  ARTIFICIAL  CROWNS. 

grasped  in  the  beaks  of  a  pair  of  forceps  and  gradually  worked  loose 
and  removed.  If  it  becomes  necessary  to  split  the  collar,  it  is  advisable 
to  make  a  new  crown.  If  the  band  and  stay  are  removed  without  split- 
ting the  collar,  a  spear-pointed  drill  is  passed  through  the  cap  at  the  base 
of  the  stay  ;  this  perforation  serves  as  a  passage  for  the  new  post.  A 
fine  bur  is  passed  around  the  post,  removing  the  cement  for  about 
half  the  depth  of  the  post.  As  a  rule,  more  or  less  incidental  enlarge- 
ment of  the  canal  is  unavoidable.  The  end  of  the  post  is  caught  between 
the  beaks  of  a  pair  of  forceps  and  gradually  worked  loose,  when  it  is 
removed.  The  remainder  of  the  cement  is  now  drilled  from  the  canal. 
The  stay  is  filed  away  at  its  anterior  face  sufficiently  to  allow  for  a 
new  stay  of  No.  33  plate.  The  collar  is  adjusted  to  the  root  and  a 
post  passed  through  the  perforation  made  in  the  cap  into  the  root 
(Fig.  846,  o).  An  impression  is  taken  in  which  ferrule  and  post  are  re- 
moved, and  a  cast  made  of  investing  material.  A  suitable  tooth  is 
selected  and  a  stay  of  No.  33  pure  gold  or  platinum  plate  burnished  to 
its  back ;  the  pins  of  the  crown  remain  unbent,  and  are  passed  into  the 
cuts  made  in  the  original  stay,  enlarging  the  latter  should  it  be  necessary. 
The  tooth  is  accurately  ground  to  position  (Fig.  846,  6),  and  when  fitted 
the  surfaces  of  the  stays  are  covered  with  borax,  the 
Fig.  846.  tooth  set  in  position,  and  investing  material  placed  over 

it,  leaving  the  palatal  surface  of  the  crown  exposed.  A 
piece  of  solder  (14-carat)  is  placed  over  each  pin,  two 
small  pieces  at  the  upper  line  of  junction  of  the  stays, 
and  q,  large  piece  over  the  exposed  end  of  the  post.  The 
case  is  thoroughly  heated  from  the  outside ;  in  fact,  it  is 
better  to  direct  the  heat  against  the  investment  covering 
the  tooth  until  the  solder  at  the  edges  flows  and  unites 
the  new  and  old  stay.  A  fine  flame  directed  against  the 
solder  over  pins  and  post  flows  it  into  the  depressions  about  them. 

Substantially  the  same  procedures  are  followed  in  removing  the  post 
and  plate  crown  when  attached  by  means  of  zinc  phosphate.  The  great 
difficulty  in  these  cases  is  in  removing  the  posts :  it  is  necessary  to 
remove  the  cement  for  some  depth  before  it  is  possible  to  loosen  them  : 
the  difficulty  is  increased  with  posts  having  the  Logan  form.  An 
opening  is  made  through  the  plate  for  the  passage  of  the  new  post, 
the  surface  of  the  stay  ground  down  for  the  reception  of  the  new  stay, 
and  the  slots  are  cut  in  the  backing  as  described.  Should  a  straight-pin 
tooth  be  employed,  holes  are  drilled  for  the  reception  of  the  pins ;  these 
openings  are  elongated  toward  the  base  of  the  stay,  so  as  to  accommo- 
date the  pins  of  the  tooth  while  it  is  being  fitted.  A  new  post  is  fitted 
and  placed  in  position,  the  impression  taken,  and  the  new  tooth  mounted 
as  in  the  operation  previously  described. 

In  removing  the  metallic  basis  of  crowns  which  have  been  attached 
by  means  of  gutta-percha  the  retaining  medium  is  to  be  softened  suf- 
ficiently to  permit  the  withdrawal  without  mutilation.  After  gutta- 
percha has  been  worn  for  a  long  period  it  becomes  difficult  to  soften. 
Probably  the  most  effective  means  of  attaining  this  end  is  to  heat  the 
jaws  of  a  pair  of  heavy  pliers ;  then,  after  protecting  the  lips  and  gum 
with  napkins,  grasp  the  stay  between  the  jaws  of  the  pliers,  and  after 
some  time  exert  traction  and  draw  the  post  from  the  root.     The  crown 


SETTING   CBOWNS  WITH  ZINC  PHOSPHATE.  645 

base  is  heated  and  the  remnants  of  gutta-percha  burned  off.  The  stay 
is  thinned  as  in  the  former  case,  and  cuts  or  holes  made  for  the  recep- 
tion of  the  pins  of  the  new  facing,  which  is  backed,  fitted,  and  attached 
as  described. 

Retaining  Media. 

The  two  materials  commonly  used  as  retentive  media  for  artificial 
crowns  are  gutta-percha  and  the  phosphate  of  zinc. 

Each  of  these  substances  possesses  properties  which  govern  their  em- 
ployment. Oxyphosphate  is  adhesive,  extremely  hard,  therefore  difficult 
of  removal,  and  is  more  or  less  soluble  in  the  fluids  of  the  mouth.  The 
greater  the  amount  of  acid  present  in  the  saliva,  the  greater  the  solubility 
of  the  cement.  It  disintegrates  most  quickly  at  the  cervical  margin, 
where  acid  formations  are  in  greatest  amount,  and  is  somewhat  porous. 
Protected  from  contact  with  the  oral  fluids,  it  lasts  indefinitely. 

Gutta-percha  is  almost  unchangeable  in  the  mouth,  is  plastic,  is  softer 
than  zinc  phosphate,  and  loses  substance  by  attrition.  It  may  be 
resoftened  by  heat,  but  softening  becomes  more  difficult  with  age. 

Therefore,  zinc  phosphate  is  selected  for  the  retentive  medium  when 
it  is  protected  from  the  fluids  of  the  mouth,  where  such  space  exists  as 
demands  more  rigidity  than  could  be  furnished  by  a  mass  of  gutta- 
percha, and  where  adhesiveness  is  a  desideratum,  where  support  is  to  be 
furnished  for  a  metal  surface  susceptible  to  change  of  shape,  as,  for 
instance,  in  a  thin  gold  crown,  where  gutta-percha,  if  used,  would  by  its 
elasticity  permit  change  of  shape  in  the  band. 

Gutta-percha  is  to  be  employed  where  the  fluids  of  the  mouth  have 
access,  where  such  a  thin  layer  of  retentive  medium  is  required  that  its 
pliability  does  not  affect  its  fixation,  or  where  it  may  be  desirable  to 
furnish  means  for  removal  of  a  crown  should  this  ever  become  desirable. 

Thus  in  all  crowns  supported  by  bands  or  barrels  which  extend 
beneath  the  edge  of  the  gum  zinc  phosphate  is  the  proper  retaining 
medium. 

Also  in  cases  where  a  large  space  exists  between  crown  and  root ; 
that  is,  an  interior  space  not  marginal,  for  marginal  adaptation  in  all 
crowns  must  be  perfect. 

In  those  crowns  which  are  placed  upon  posts  which  have  been  fixed 
in  roots  to  serve  as  supports  to  porcelain  crowns  or  faces  the  retentive 
medium  becomes  practically  part  of  the  crown. 

Setting  Crowns  with  Zinc  Phosphate. 

The  zinc  phosphate  employed  in  the  setting  of  crowns  should  possess 
the  characteristics  which  would  recommend  the  specimens  to  be  used  as 
filling  material.  It  should,  however,  flow  freely,  and,  as  the  difficulty 
of  maintaining  dryness  is  increased,  it  should  set  promptly  and  yet 
with  sufficient  deliberation  to  permit  the  accurate  adaptation  of  the 
crowns.  The  operator  should  by  actual  test  determine  precisely  the 
peculiarities  of  the  particular  cement  he  is  to  employ.  Specimens  of 
zinc  phosphate  differ  so  markedly  in  their  behavior  that  it  is  always 
wise  to  make  preliminary  tests  of  each  package. 

In  setting  post  crowns  with  zinc  phosphate  the  following  will  be 
found  a  satisfactory  method  :  The  root  is  protected  from  the  access  of 


646  ARTIFICIAL   CROWNS. 

moisture,  cleansed  with  strong  pyrozone,  and  dried  by  means  of  the 
hot  blast.  A  couple  of  drops  of  the  cement  fluid  are  placed  on  a  mix- 
ing slab,  and  beside  it  an  excess  of  powder ;  the  latter  is  to  be  gradually 
combined  with  the  fluid,  adding  little  by  little  and  mixing  well  with  a 
spatula  until  the  paste  is  thick  enough  to  be  rolled  into  a  pellet  which 
changes  shape  through  its  own  weight.  A  pellet,  rolled  long,  is  passed 
into  the  root ;  the  post  and  under  surface  of  the  crown  are  covered  with 
cement  and  pressed  quickly  into  the  root ;  the  surplus — and  there  should 
always  be  a  surplus — is  squeezed  from  about  the  edges  of  the  crown. 
The  napkin  is  held  in  position  and  dryness  maintained  until  the  cement 
on  the  slab  is  hard  and  resists  the  edge  of  a  knife-blade. 

The  advantages  of  gutta-percha  covering  the  root  face  and  the  rigid 
phosphate  filling  the  pulp-canal  may  be  both  had  by  the  following  method : 
A  thin  disk  of  gutta-percha  is  perforated  and  passed  over  the  post  and 
pressed  against  the  base  of  the  crown.  It  is  then  set  upon  a  gutta-percha 
heater.  The  root  is  thoroughly  dried,  and  the  zinc  phosphate  placed  in 
the  canal.  The  crown  is  firmly  pressed  into  position,  the  surplus  cement 
emerging  from  beneath  the  edge  of  the  crown  and  the  gutta-percha  being 
reduced  to  a  thin  film. 

Another  method  of  combining  the  two  media,  applicable  to  roots 
which  have  suffered  much  loss  of  tooth-substance  about  the  periphery 
of  the  canal,  is  as  follows :  A  stick  or  wire  the  size  of  the  crown-post  is 
smoothed  and  covered  with  vaseline  or  any  oil  to  prevent  the  adhesion 
of  the  cement  to  its  surface.  The  root  is  filled  with  cement,  and  the 
greased  post  thrust  into  it,  and  moved  about  slightly  to  press  the  cement 
away  from  it  to  permit  its  easy  withdrawal.  When  the  cement  has  set 
all  portions  which  interfere  with  the  proper  placement  of  the  crown  are 
removed,  and  the  crown  mounted  with  gutta-percha  as  described. 

In  setting  barrel  crowns  the  root  is  dried  and  protected  by  napkins ; 
the  cement  is  mixed  thinner  than  for  setting  post  crowns ;  the  irregular 
parts  and  undercuts  of  the  root  are  filled  with  the  cement ;  and  a  portion 
of  the  plate  is  flowed  into  the  deepest  portions  of  the  crown,  which  is 
then  promptly  set  in  position  over  the  root  and  firmly  pressed  into  posi- 
tion. A  piece  of  tin-foil  (No.  20)  is  doubled  and  set  over  the  surface  of 
the  crown ;  the  napkin  is  removed  and  the  patient  is  directed  to  close 
the  jaws,  and  hold  them  firmly  closed  until  it  is  seen  by  testing  the 
cement  on  the  slab  that  it  has  hardened.  It  is  the  usual  practice  to  per- 
forate barrel  crowns  in  the  deepest  point  of  the  masticating  surface  to 
permit  the  escape  of  air  and  the  surplus  cement.  The  opening  thus 
made  is  to  be  filled  with  gold-foil  when  the  cement  is  fully  hardened. 

In  setting  the  post  and  collar  crowns  a  cone  of  soft  cement  is  placed 
in  the  root-canal ;  the  concavity  of  the  ferrule  is  filled  with  cement,  and 
the  crown  is  pressed  into  position.  After  the  cement  has  set  a  fine  in- 
strument is  to  be  passed  around  the  margin  of  the  collar  or  barrel  to 
remove  any  particles  of  surplus  cement.  Should  any  of  these  fragments 
remain,  they  may  form  a  source  of  serious  irritation  to  the  soft  tissues. 

Setting  of  Crowns  with  Gutta-percha. 

The  office  of  the  retaining  medium  is  twofold — first,  to  furnish  a 
structure   which   shall   serve  as  a  mechanical   support   throughout   its 


SETTING   OF  CROWNS   WITH  GUTTA-PERCHA. 


647 


length  and  surface,  to  restore  any  imperfections  of  union  between  the 
root  and  the  crown,  so  that  the  two  factors  are  bound  together  in  a  fixed 
mechanical  unit.  Secondly,  the  medium  is  to  act  as  a  protector  to  the 
surfaces  of  the  root  against  the  encroachment  of  the  active  causes  of 
dental  caries. 

It  will  be  seen,  therefore,  that  the  retaining  medium,  whether  it  be 
gutta-percha  or  zinc  phosphate,  is  to  be  so  manipulated  that  it  sHall  per- 
fectly fill  the  minute  interstices  of  the  parts  it  unites. 

When  gutta-percha  is  to  be  employed,  it  is  necessary  that  the  several 
parts  shall  be  at  a  temperature  which  will  permit  the  ready,  deliberate, 
and  accurate  adjustment  of  the  crown  and  gutta-percha  to  the  root. 

A  satisfactory  method  of  manipulation  is  as  follows  :  A  napkin  is 
adjusted  so  that  the  root  is  protected  from  moisture  ;  the  canal  is  wiped 
out  with  caustic  pyrozone.  The  post  is  now  barbed,  so  that  the  gutta- 
percha will  be  mechanically  held  to  it :  a  sharp  enamel-chisel  or  knife- 
blade  is  used  to  nick  the  post. 

The  crown  is  laid  upon  a  gutta-percha  heater  (Dr.  How's  steatite  slab 
is  useful  for  this  purpose),  a  piece  of  tough  gutta-percha  is  laid  beside 
the  crown,  and  when  soft  is  pressed  out  between  the  fingers  into  a  sheet, 

Fig.  847. 


How's  heater. 


which  is  wrapped  around  the  heated  post.  The  root-canal  is  wnped  out 
with  oil  of  cloves,  so  that  the  gutta-percha  will  not  adhere  to  it,  and  the 
heated  crown  and  softened  gutta-percha  are  pressed  into  position.  If  an 
excess  of  gutta-percha  has  been  applied,  the  surplus  will  be  squeezed 
from  beneath  the  outlines  of  the  crown.  This  excess  is  to  be  trimmed 
away  by  means  of  sharp  scissors.  If  there  has  not  been  sufficient  gutta- 
percha attached  to  the  post,  more  is  to  be  added  to  that  on  the  post  and 
the  crown  reapplied,  and  then  the  excess  trimmed  off.  The  crown  is 
returned  to  the  heater,  which  is  again  held  over  the  flame  until  the  fusible 
metal  melts.  A  fresh  napkin  is  placed  in  position ;  the  root  is  wiped 
out  with  chloroform  and  dried  by  means  of  a  hot  blast.  A  small  sheet 
of  softened  gutta-percha  is  added  about  the  post,  and  when  the  crown 
and  gutta-percha  are  thoroughly  heated  the  crown  is  seized  between  the 
fingers,  protected  by  a  napkin,  and  pressed  into  position.  A  heated 
crown  adjuster  (see  Fig. —  )  is  now  applied  to  the  crown,^and  it  is  forced 
into  position ;  the  excess  of  gutta-percha  is  squeezed  out  at  the  margins 
of  the  crown. 


CHAPTER    XIX. 

AN  ASSEMBLAGE  OF  UNITED  CROWNS  (BRIDGE- WORK). 

By  H.  H.  Buechaed,  M.  D.,  D.  D.  S. 


A  DENTAL  bridge  is  essentially  a  continuous  masticating  surface 
anchored  to  supporting  abutments  at  two  or  more  points  of  its  length, 
the  fixation  and  retention  of  the  device  depending  upon  anchorage  on 
or  in  the  natural  teeth ;  any  support  derived  through  contact  of  the 
appliance  with  the  natural  gum  is  purely  secondary.  The  method  and 
variety  of  support  are  the  direct  reverse  of  those  of  an  artificial  denture 
mounted  upon  a  plate,  for  here  the  primary  support  is  by  the  natural 
gum,  and  any  further  support  derived  through  attachment  to  the  natural 
teeth  is  merely  adjunctive. 

The  appliances  in  contemporary  use  which  are  included  under  the 
head  of  "  dental  bridges "  comprise  a  multitude  of  devices,  the  con- 
struction and  support  of  which  depend  upon  a  few  principles.  The 
many  different  forms  are  modifications  of  a  limited  number  of  types, 
the  differences  between  many  of  apparently  diverse  types  being  merely 
technical  and  not  those  of  mechanical  principles. 

The  natural  teeth  or  roots  supporting  the  bridge  are  called  its  "  abut- 
ments," the  crowns  placed  over  them  or  the  bars  anchored  in  them,  the 
"  abutment  pieces."  The  intervening  portions  of  the  fixture  are  known 
as  "  the  body  of  the  bridge,"  and  the  several  pieces  of  which  it  is  com- 
posed, "  the  dummies." 

HiSTOEY. — Devices  which  might  be  classed  as  dental  bridges  are 
probably  as  old  as  the  earliest  attempts  at  dental  prosthesis.  The  placing 
of  a  band  of  metal  about  one  natural  tooth  is  the  simplest  means  for 
supporting  an  additional  tooth,  and  probably  the  first  attempted. 

Among  the  archaeological  remains  of  the  Etruscan  life  are  found 
devices  which  bear  a  family  resemblance  to  bridge-work. 

The  present  varieties  included  in  the  generic  name  of  dental  bridges 
are  the  evolution  of  processes  and  types  suggested  and  made  early  in 
this  century.  As  an  example  of  an  early  device  bearing  a  close  resem- 
blance to  a  contemporary  appliance.  Dr.  W.  F.  Litch  ^  gives  a  cut  from 
the  work  of  F.  Maury  (1828),  showing  six  anterior  teeth  anchored  in 
the  roots  of  the  cuspids  by  means  of  two  posts  placed  in  the  enlarged 
pulp-canals. 

In  April,  1855,  Dr.  Wm.  H.  Dwindle^  described  the  progenitor  of 
the  modern  pin  and  plate  bridge,  together  with  the  prototype  of  another 
form  of  bridge  in  present  use  :  "  After  the  root  is  filled  with  gold  .... 

^  American  System  of  Dentistry,  vol.  ii.,  Fig.  758. 
^  American  Journal  of  Dental  Science. 


CLASSIFICATION  OF  BRIDGES. 


649 


and  properly  finished,  an  impression  of  its  surface  is  taken  in  wax,  from 
which  castings  are  made,  and  from  these  plates  are  swaged.  These  are 
adjusted  to  the  tooth  and  a  golden  pivot  soldered  to  the  upper  surface. 
A  plate  tooth  is  now  skilfully  adapted  to  the  fixture,  when  it  is  ready 
for  use.  In  this  way  a  plate  may  be  carried  aci^oss  an  intervening  space 
unoccupied  by  roots,  and  an  unbroken  roiv  of  teeth  mounted  upon  it." 
In  January,  1871,  Dr.  Benj.  J.  Bing  applied  for  a  patent  for  a  bri 
to  be  anchored  by  wire  extremities  into  cavities  in  the 


devic 
teeth. 


dge 
natural 


Fig, 


A  form  of  removable  bridge  was  introduced  by  Dr.  W.  G.  A.  Bonwill 
in  1873  (Fig.  848). 

The  revival  of  bridge-work,  or  the  modern  ideas  of  these  forms  of 
appliance,  arose  with  the  advent  of  the  barrel 
and  collar  crowns.  This  variety  of  crown, 
made  and  applied  early  in  the  century,  ap- 
pears to  have  had  very  limited  employment 
until  its  elaboration  by  Dr.  C.  M.  Richmond. 
The  primary  principle  involved  was,  as  stated, 
known  and  applied  for  many  years  ;  it  is  but 
fifteen  years,  however,  since  the  general  adop- 
tion of  the  idea. 

In  its  simplest  form  a  dental  bridge  con- 
sists of  two  or  more  crowns  bearing  between,  V. 
and   rigidly  attached  to,  them  substitutes  for 

the  crowns  of  the  intervening  natural  teeth  which  have  been  lost.  The 
primary  object  sought  has  been  disuse  of  a  plate,  and  such  firmness  and 
immobility  as  would  furnish  a  better  means  in  mastication  than  is  pos- 
sible with  a  plate  denture. 


Fig.  849. 


Classification  of  Bridges. 

Dental  bridges  may  be  divided  into  two  primary  classes — fixed  or 
removable. 

Fixed  bridges  are  those  which  are  so  attached  to  the  abutments  that 
removal  of  a  properly  fitted  and  adjusted  piece 
is  not  practicable  without  more  or  less  mutila- 
tion of  the  abutment  crowns  (Fig.  849). 

Removable  bridges  are  those  whose  support- 
ing crowns  may  be  detached  from  the  abutments 
without  disturbing  the  integrity  of  the  appli- 
ance. 

Class  1  may  be  subdivided  into  sub-classes 
according  to  the  method  and  means  of  anchor- 
age : 

Sub-class  1  :  Those  attached  to  the  abutments 
by  means  of  collar  or  barrel  crowns  (Fig.  849). 

Sub-class    2 :    Those    in  which    fixation    is 
secured  by  means  of  metallic  bars  anchored  in  the  crowns  or  roots  of 
teeth.     (See  Porcelain  Bridges.) 

The  features  of  both  sub-classes  may  be  combined  in  one  piece,  a 
bar  anchorage  at  one   extremity  and  a  collar  or  barrel  crown  at  the 


650  AN  ASSEMBLAGE  OF   UNITED   CROWNS. 

other  (Fig.  850).  Devices  of  the  varieties  of  Dr.  Litch's  pin  and 
plate  bridge  belong  to  sub-class  2 ;  the  open-cylinder  partial  crown 
terminals  to  sub-class  1. 

The  usual  forms  of  removable  bridges  have  abutment  crowns  made 

of  cylinders,  which  telescope  over  metallic  ferrules  which  have  been  per- 

^        -„  manently  attached  to  the  abutments.     This  form 

of  bridge  was  devised  to  facilitate  removal  when 

repair  of  the  piece  became  necessary ;  to  permit 

of  occasional  removal,  so  that  the  bridge  might 

be  perfectly  cleansed;  to  furnish  a  method  of 

attachment  when  the  abutment  teeth  were  in  such  malposition  that  a  fixed 

bridge  could  not  be  attached  without  undue  mutilation  of  natural  crowns. 

The  introduction  of  the  removable  bridges  has  negatived  several  of 
the  objections  urged  against  the  practice  of  this  work.  First,  the  want 
of  perfect  cleanliness,  for  removable  bridges  may  be  detached  when  neces- 
sary and  receive  a  perfect  cleansing.  In  case  of  repair  being  necessary 
the  piece  may  be  removed  without  mutilation  of  the  abutment  crowns. 
It  furnishes  a  means  for  bridging  spaces  enclosed  by  overhanging  teeth. 
These  bridges  possess  so  many  advantages  over  the  fixed  variety  that  it 
is  probable  they  will  largely  supersede  the  latter. 

A  type  of  device  somewhat  resembling  a  bridge  has  been  constructed 
and  described,  which  combines  some  of  the  features  of  both  bridge  and 
plate.  Extending  from  the  terminal  abutment  pieces  of  a  bridge  are 
arms  or  wings  resting  upon  the  gum  and  supporting  one  or  more  arti- 
ficial teeth  on  each  of  them.  The  mechanical  principle  involved  in  this 
device  is  faulty.  The  plate  pieces  to  furnish  any  material  support  must 
be  of  such  size  as  to  render  the  appliance  highly  objectionable  hygieni- 
cally;  and  if  too  small  to  serve  as  effective  auxiliary  supports,  the  abut- 
ments are  overstrained  (Fig.  829). 

In  judging  of  the  merits  and  demerits  of  this  phase  of  prosthesis,  it 
would  be  manifestly  improper  to  accept  all  the  claims  of  the  enthusiastic 
advocates  or  to  be  governed  by  the  opinions  of  its  pronounced  opponents. 

The  advantages  claimed  for  bridge-work  are  the  removal  of  many  of 
the  deficiencies  associated  with  plate  dentures.  First,  the  bridge  is  im- 
movable ;  second,  there  is  no  interference  with  articulation  ;  third,  teeth 
may  be  replaced  without  the  necessity  of  wearing  a  cumbrous  plate.  The 
several  advantages  enumerated  by  advocates  may  be  all  summed  up  under 
these  three  headings. 

The  objections  urged  against  bridge-work  in  the  past  have  been  in 
great  measure  removed ;  others  remain.  It  does  not  restore  lost  gum 
contour,  except  with  those  devices  known  as  plate  bridges.  It  is  un- 
cleanly ;  the  spaces  existing  between  portions  of  the  bridge  surface  and 
the  natural  gum  are  frequently  inaccessible  to  the  tooth-brush  and  con- 
tain decomposing  food  debris.  Teeth  are  necessarily  mutilated  to  serve 
as  correct  abutments.  It  is  frequently  necessary  to  destroy  vital  pulps. 
The  abutments  may  be  subjected  to  a  greater  mechanical  stress  than 
they  can  safely  bear.     Difficulty  of  repair  has  been  a  serious  objection. 

The  intrinsic  merit  of  properly  constructed  bridge-work  is  undoubted. 
Many  of  the  objections  stated  above  do  not  attach  to  properly  designed 
and  constructed  pieces ;  they  are  based  upon  such  practice  of  bridge- 
work  as  is  now  regarded  as  unjustifiable. 


CLASSIFICATION  OF  BRIDGES.  651 

It  is  to  be  recognized  that  neither  bridge-  nor  plate-work  is  of  uni- 
versal application ;  each  case  presents  indications  which  should  determine 
what  form  of  prosthesis  is  applicable. 

The  work  has  unquestionably  a  great  field  of  useful  application  :  cases 
there  are  in  which  this  type  of  fixture  is  a  well-defined  need,  and  others 
in  which  it  is  clearly  contraindicated. 

The  first  inquiry  of  the  operator  should  be,  Is  a  bridge  demanded  by 
the  conditions  present  ?  that  is,  Does  a  bridge  device  possess  for  the  case 
in  hand  sufficient  advantage  over  a  plate  denture  to  render  its  use  an 
imperative  indication  ?  Upon  this  point  turns  the  entire  subject  of  the 
wisdom  or  unwisdom  of  bridge-work. 

The  student  is  assured  that  in  the  practice  of  this  special  field  he  will 
find  application  for  an  exhaustive  knowledge  of  dental  pathology,  thera- 
peutics and  mechanics,  combined  with  rare  manipulative  ability;  in  point 
of  fact,  the  work  should  not  be  done  unless  the  operator  possess  this  de- 
gree of  knowledge  and  skill. 

The  requisites  for  its  correct  practice  mark  the  mechanical  and  phys- 
iological aspects  of  bridge-work. 

Mechanical  Aspect. — Under  the  mechanical  aspect  are  included  all 
considerations  of  resistances  to  stress  and  the  effect  of  stress  as  expressed 
in  the  mobility  of  the  bridge,  of  any  part  of  it,  or  of  its  abutments.  The 
same  considerations  governing  the  mechanical  resistance  of  roots  or  teeth 
when  serving  as  bases  for  artificial  crowns,  apply  with  increased  emphasis 
when  they  are  to  be  the  abutments  of  a  bridge  piece. 

The  student  is  presumably  familiar  with  the  anatomy  and  the  ana- 
tomical variations  of  the  teeth  as  to  their  forms,  structure,  and  positions. 

Any  stress  greatly  in  excess  of  the  amount  normally  borne  is  a 
menace  to  the  integrity  of  a  tooth's  retention.  The  increased  mechanical 
stress  reacts  physiologically,  and  by  a  pathological  process  the  tooth  is 
loosened  and  lost. 

The  vertical  is  the  only  direction  of  force  which  does  not  tend  to 
mechanically  dislodge  a  tooth,  and  it  is  one  to  M'hich  teeth  are  rarely 
subjected  alone.  As  a  rule,  teeth  protest  against  stress  received  in  any 
direction  other  than  that  due  to  their  anatomical  forms  and  positions. 
Incisors  are  by  these  factors  designed  to  meet  and  resist  stress — to  move 
in  one  direction,  either  outward  or  inward.  The  broadest  aspect  of  their 
root  is  anterior,  offering  at  this  part  the  greatest  resistive  surface. 

The  cuspids  receive  the  force  in  two  directions,  each  at  an  angle  with 
the  axis  of  the  tootli :    the  resultant  of  the  forces  (the  direction  of  the 
movement  of  the  tooth)  is  between  the  two  forces.    Accord- 
ing as  the  greater  impact  is  anterior  or  posterior  will  be  the       Fig.  851. 
movement  (Fig.  851). 

The  bicuspids  normally  receive  three  main  lines  of  force 
—an  outward,  an  inward,  and  a  vertical :  the  outward  and 
inward  forms  are  the  resultants  each  of  two  forces  acting 
upon  the  cusps  at  an  angle  with  the  axis  of  the  tooth. 

The  muscular  force  being  equal,  the  longer  the  cusps  the 
greater  will  be  the  lateral  stress ;  also  the  broader  the  cusps 
(the  farther  their  external  walls  are  removed  from  the  axes  of  the  teeth) 
the  greater  stress  there  will  be  in  all  three  directions. 

The  molars  also  receive  force  in  three  main  directions,  but  the  lateral 


652  AN  ASSEMBLAGE  OF   UNITED  CROWNS. 

forces  are  the  resultants  of  several  lines  of  force  according  to  the  sizes 
and  positions  of  the  cusps. 

The  resistances  to  these  stresses  are  through  the  forms,  number,  sizes, 
and  structure  of  the  roots,  and  also  of  their  supporting  structures. 

Dr.  Bonwill  has  demonstrated  a  constant  relationship  between  the 
lengths  of  the  cusps  and  the  amount  of  over-bite,  and  as  a  consequent 
the  extent  of  the  contact  of  the  cusps  in  mastication.  The  greater  the 
over-bite  the  greater  surface  of  contact  there  must  be,  and,  other  things 
being  equal,  the  greater  mechanical  stress.  This  is  an  important  con- 
sideration, and  one  to  be  constantly  borne  in  mind  in  the  making  and 
adjusting  of  crowns  and  bridges. 

No  absolute,  or  perhaps  even  proximate,  rules  can  be  formulated  as 
to  the  amount  of  strain  any  single  tooth  will  bear :  attempts  at  the 
formulation  are  delusive. 

Given  two  central  incisors,  the  amount  of  resistance  either  will  afford 
depends,  first,  upon  the  anatomical  form  and  support  of  each,  and  their 
relative  positions  to  their  antagonists,  and  is  governed  largely  by  the 
physiological  condition  of  each.  Alter  the  relations  in  any  particular, 
and  the  resistance  is  correspondingly  modified. 

By  uniting  or  splinting  together  several  teeth,  as  in  a  bridge  piece, 
the  movement  of  each  tooth  is  modified  or  restrained,  and  by  such  fixa- 
tion two  natural  teeth  are  frequently  found  to  successfully  withstand 
more  force  than  the  sum  of  their  individual  resistances.  As  an  illustra- 
tion observe  a  common  condition  in  which  a  bridge  is  applied — an  inferior 
second  bicuspid  and  a  third  molar  serving  as  abutment  teeth.  If  these 
teeth  be  healthy  and  have  firm  attachment,  fixing  to  them  a  rigid  bridge 
piece  prevents  the  tendency  toward  antero-posterior  displacement,  one  of 
the  strongest  elements  tending  toward  their  loss ;  they  are  held  by  the 
bridge  so  that  the  only  possible  movement  is  lateral. 

If  the  lateral  stress  be  correctly  governed,  such  teeth  may  safely  bear 
crowns  upon  their  own  roots,  and  support  intervening  crowns,  filling  the 
space  between  them,  for  a  longer  period  than  were  a  bridge  not  applied. 

One  of  the  most  common  faults  of  bridge-work  is,  however,  increas- 
ing strains  without  due  regard  to  the  available  resistance. 

Using  the  same  bridge  for  illustration,  the  abutments  are  subjected  to 
the  amount  of  stress  normally  borne  by  four  teeth.  It  depends  upon  the 
directions  of  the  root-axes  whether  the  resistance  of  the  abutments  when 
barred  together  is  increased  in  the  same  degree  as  the  stress.  Their 
antero-posterior  movement  is  effectually  checked,  but  if  the  roots  of  the 
teeth  have  parallel  axes,  both  are  free  to  react  upon  lateral  stress.  While 
abutment  teeth  submit  without  protest,  as  a  rule,  to  the  direct  vertical 
force  of  mastication,  occasionally  there  will  be  found  a  progressive  degen- 
eration of  the  pericementum,  which  causes  loosening  of  these  teeth. 

The  lateral  stress  is  the  one  tending  to  dislodge  bridge  fixtures,  and 
the  tendency  to  displacement  is  increased  in  the  ratio  of  this  stress,  hence 
the  longer  the  cusps,  and  the  more  accurate  their  occlusal  union  with  the 
antagonizing  teeth,  the  greater  the  stress  upon  the  abutments. 

Bridge-work  should  be  constructed  upon  sound  mechanical  principles : 
to  be  successful  as  a  piece  of  engineering  work  all  designs  are  to  be 
founded  upon  those  principles.  These  fixtures  are  literally  bridges,  a 
continuous  surface  supported  by  rigid  abutments,  designed  to  bear  safely 


CLASSIFICATION  OF  BRIDGES. 


653 


the  amount  of  stress  it  is  calculated  the  piece  will  be  subjected  to.  The 
calculations  involve  the  strengths  of  abutments,  crowns,  and  body  of  the 
bridge.  Violations  of  sound  engineering  principles  are  common  in  sug- 
gested devices  :  the  student  should  examine  carefully  all  proposed  de- 
signs and  select  only  those  which  are  mechanically  good. 

An  engineer  recognizes  that  the  stability  and  permanence  of  his  bridge 
depends  primarily  upon  the  strength  and  position  of  its  abutments.  If 
these  be  badly  built  or  poorly  sustained,  the  bridge  fails ;  so  that  bases 
are  selected  and  prepared,  abutments  built,  with  a  due  regard  for  the 
weight  they  are  to  sustain,  the  resistance  they  are  to  afford. 

With  dental  bridges,  utilizing  any  but  sound  teeth  or  roots,  those  free 
from  pericementitis  or  abscess,  is  equivalent  to  an  engineer  building  abut- 
ments in  a  marsh  without  piles. 

In  designing  a  bridge  note  the  directions  of  the  least  and  greatest  re- 
sistances, and  apply  the  strains  accordingly,  and  mould  the  articulation 
so  that  the  greatest  force  shall  be  opposed  to  the  greatest  resistance  and 
vice  versa.  To  illustrate  :  teeth  which  have  their  axes  parallel  and  in  the 
same  plane  (Fig.  852,  A),  all  other  things  being  equal,  will  withstand  less 
stress  than  were  the  axes  not  parallel  and  in  different  planes  (Fig.  852,  B) ; 

Fig.  852, 


that  is,  when  the  teeth  in  both  cases  are  serving  as  bridge  abutments : 
with  parallel  axes,  when  one  abutment  moves  in  the  direction  of  least 
resistance  its  fellow  abutment  moves  with  it ;  but  if  the  axes  be  not 
parallel,  when  one  abutment  is  subjected  to  stress  in  the  line  of  least 
resistance  its  fellow  is  receiving  the  stress  in  a  line  of  greater  resistance. 
Another  illustration  is  found  in  a  common  form  of  bridge — ^two  cus- 
pid roots  supporting  artificial  crown  substitutes  of  the  six  anterior  teeth 
(Fig.  853).  With  all  of  the  posterior  teeth  in  position  the  amount  of 
strain  on  the  abutments  is  governed  first  by  the  lengths  of  the  crowns, 
the  leverage  on  the  roots ;  next  upon  the  amount  of  over-bite  or  the 
extent  of  incisive  action  occurring  before  the  occlusion  of  the  posterior 


654  AN  ASSEMBLAGE  OF   UNITED  CROWNS. 

teeth  equalizes  the  forces.    In  the  ratio  of  the  stress  is  the  demand  for 
increased  resistance :  such  cases  form  bulkheads,  and  if  the  displacing 

force  be  great,  the  ends  of  the   bulkhead   re- 
FiG.  853.  quire  reinforcement  through  additional  abut- 

ments. 

The  force  of  occlusion  applied  to  a  bridge 
anchored  by  terminal  bars  tends  to  swing  the 
piece  as  though  held  in  trunnions — moreover, 
to  draw  the  bars  from  the  anchorage  teeth 
(Fig.  854,  A).  It  is  evident  that  to  securely 
fasten  such  pieces  the  ends  must  be  so  formed,  so  placed,  and  of  such 
size  as  to  resist  tendencies  inherent  in  this  pattern  of  bridge  (Fig. 
854,  B,  C). 

Q  Fig.  854. 


To  ensure  the  stability  of  a  bridge  it  should  be  so  made  and  so 
attached  to  its  abutments  that  neither  bridge  nor  any  part  of  it  has  any 
movement  independent  of  the  abutments.  Violations  of  this  rule  are 
found  where  caps  are  made  of  too  thin  metal,  which  by  stretching  or 
breaking  permits  slight  loosening  of  the  piece  ;  the  retaining  cement  is 
worn  away  piecemeal,  and  the  space  left  is  filled  with  fermenting  debris  : 
decalcification  of  the  enamel  and  caries  ensue. 

Retaining  caps  are  frequently  made  with  merely  a  narrow  band 
encircling  the  labial  wall  of  the  neck  of  the  tooth.  Unless  these  bands 
are  made  of  rigid  metal  they  will  become  loose,  and  they  acquire  a  slight 
mobility  upon  the  tooth ;  the  underlying  cement  is  dislodged,  and  it  is 
not  uncommon  to  find  an  area  of  decalcified  enamel  beneath  them. 

Bar  anchorages  should  be  so  formed  and  attached  that  they  become 
mechanically  a  continuation  of  the  abutment  itself. 

With  decreasing  amount  of  resistance  offered  by  the  abutments 
should  be  a  decrease  of  the  extent  of  masticating  or  incisive  surface ; 
for  example,  two  abutment  crowns,  a  firmly  fixed  molar  and  cuspid, 
having  healthy  root  support,  may  have  the  original  amount  of  masti- 
catory surface  restored ;  but  if  the  fixation  of  the  abutments  be  less 
rigid  or  not  in  so  good  a  physiological  condition,  the  amount  of  the 
surface  should  be  diminished. 

Physiological  Aspect. — The  physiological  aspect  of  bridge-work, 
although  belonging  properly  to  works  upon  dental  pathology,  must  form 
part  of  every  treatise  upon  such  a  combination  of  surgery  and  mechanics 
as  bridge-work  represents.  It  includes  the  consideration  of  all  of  the 
vital  relations  of  the  abutment  teeth,  the  contiguous  parts,  and,  it  may 
be,  of  more  general  vital  relations.  Anything  directly  or  indirectly 
bearing  upon  the  subject  of  dental  hygiene  is  an  item  for  consideration 
in  the  pursuit  of  this  work. 

The  first  question  is  that  of  the  physiological  resistance  of  the  abut- 
ments, and  the  danger,  immediate  or  remote,  of  any  disease  process 
occurring  in  or  about  them.     These  include  the  possibilities  of  enamel 


CLASSIFICATION  OF  BRIDGES.  655 

decalcification,  caries  of  the  dentine,  eburnitis,  any  stage  or  degree  of 
pulp  irritation  or  inflammation,  and  any  variety  or  degree  of  pericemen- 
titis. The  possibility  or  probability  of  any  one  or  more  of  these  con- 
ditions arising  must  be  a  governing  factor  in  determining  the  form  of 
bridge  to  be  applied. 

Due  consideration  must  be  given  to  the  possibility  of  disease  process  of 
the  soft  tissues — whether  through  too  great  or  improper  character  of  con- 
tact the  gums  be  irritated  by  pressure  or  the  contact  of  sharp  edges,  or 
the  forming  of  spaces  in  which  decomposing  food  may  act  as  an  irritant 
to  mucous  surfaces. 

The  decalcification  of  an  enamel  surface  embraced  by  a  portion  of  the 
bridge  arises  from  lactic  acid,  the  product  of  a  specific  fermentation  of 
starchy  foods  gaining  access  to  surfaces  from  which  it  is  not  removed, 
due  either  to  the  carelessness  of  a  patient  or  to  his  inability  to  remove 
it  owing  to  the  peculiar  situation. 

Under  narrow  bands  or  where  the  retaining  cement  is  exposed  to  the 
access  of  the  fluids  of  the  mouth,  after  a  variable  length  of  time  it  is 
meciianically  dislodged,  or  it  may  be  dissolved,  leaving  a  space  which 
fills  with  fermenting  materials  inaccessible  to  the  tooth-brush.  Pockets 
made  by  some  surface  of  the  bridge  and  an  uncovered  enamel  surface 
become  filled  with  fermenting  deposits,  which  if  not  removed  produce 
decalcification  of  the  enamel  surface.  If  these  spaces  remain  undetected, 
caries  follows,  and  it  may  be  exposure  and  disease  of  the  pulp,  and  sub- 
sequently of  the  pericementum. 

Bridges  should  be  so  made  and  so  placed  that  even  less  opportunity 
is  given  for  the  action  of  the  products  of  fermentation  upon  tooth-tissues 
than  before  the  placement  of  the  bridge. 

Any  part  of  a  tooth's  surface  which,  through  the  fixing  of  a  bridge, 
is  placed  beyond  the  access  of  the  ordinary  cleansing  agents  employed 
by  patients  should  be  protected  from  the  ingress  or  contact  of  ferments 
or  fermentable  material  by  having  a  portion  of  the  bridge  act  as  an 
impenetrable  and  impermeable  shield. 

Another  possible  source  of  disturbance,  one  which  may  affect  the 
nutritive  functions  of  the  pulp,  will  be  found  in  teeth  which  have  been 
denuded  of  enamel  by  their  preparation  to  serve  as  abutments.  The 
pulp  may  receive  abnormal  stimulus  through  the  irritation  of  the  con- 
tents of  the  dentinal  tubuli  or  have  an  increased  conduction  of  thermal 
influence,  and  secondary  deposits  may  occur  in  the  pulp. 

The  question  of  subsequent  pericementitis  in  an  abutment  tooth,  if 
the  tooth  be  pulpless,  depends  largely  upon  the  thoroughness  with  which 
the  pulp-canal  and  dentine  have  been  sterilized,  and  the  completeness 
with  which  an  impenetrable  barrier  has  been  placed  between  the  pulp- 
canal  and  the  tissues  of  the  apical  space ;  second,  upon  the  former  con- 
dition of  the  root,  as  a  part  once  inflamed  has  an  increased  susceptibility 
to  a  recurrence  of  inflammation ;  third,  overstraining  the  abutments, 
causing  a  chronic  pericementitis  and  a  gradual  loss  of  the  alveolar  tis- 
sues ;  fourth,  the  existence  of  a  dyscrasia  which  may  in  the  future  cause 
phagedenic  pericementitis.  Should  any  of  the  pathologic  states  be 
present,  they  must  receive  appropriate  treatment  before  the  fixation  of 
the  bridge.  Should  they  arise  subsequently,  each  must  receive  thera- 
peutic aid. 


656 


AN  ASSEMBLAGE  OF   UNITED   CROWNS. 


The  muco-periosteum  of  the  alveolar  ridge  most  suitable  for  the  con- 
tact of  bridge  pieces  is  that  exhibiting  firm  texture  and  pink  color. 
When  placed  in  mouths  exhibiting  a  catarrhal  condition  increased  care 
is  demanded  that  there  be  no  inaccessible  pockets  in  which  fermenting 
material  may  find  lodgement. 

When  the  retaining  medium  of  a  bridge  is  zinc  phosphate,  it  should 
be  so  protected  by  the  bridge  that  the  fluids  of  the  mouth  have  little  or 
no  access  to  it. 

Bridges  retained  by  bar  anchorages  should  have  the  margins  of  the 
retaining  fillings  finished  with  the  same  care  and  thoroughness  as  if  they 
were  to  subserve  alone  the  ordinary  purpose  of  a  filling.  Moreover,  the 
margins  of  such  fillings  should  be  accessible  to  cleansing  agents,  for  there 
is  a  probability  of  caries  resulting  from  non-observance  of  the  rule. 

Contact  of  any  portion  of  a  bridge  with  the  natural  gum  should  be 
of  such  a  nature  that  there  is  established  no  source  of  irritation  to  it, 
either  through  roughness,  sharp  edges,  undue  pressure,  or  inaccessible 
pockets. 

Preparation  of  Abutments. — First  and  most  important,  any  root  or 
tooth  which  it  is  designed  to  make  the  abutment  of  a  dental  bridge 
should  have  such  preliminary  treatment  as  will  bring  it  to  a  condition 
of  health.  The  directions  given  as  to  the  preparation  of  roots  for  the 
reception  of  artificial  crowns  apply  with  redoubled  force  when  these  roots 
are  to  be  abutments.     The  same  requirements  as  to  perfect  adaptation 

Fig.  855. 
A  A 


of  individual  crowns  also  obtain  when  such  pieces  are  to  serve  as  the 
abutment  crowns  of  bridges.  The  contact  of  every  crown  edge  with  its 
base  should  be  perfect,  and  each  crown  should  represent  as  carefully 
made  and  adjusted  a  piece  as  were  the  same  crown  to  stand  alone. 

After  all  preparations  of  the  bases  have  been  made,  so  that  single 
crowns  may  be  properly  adapted,  there  arises  the  consideration  of  the 


CLASSIFICATION  OF  BRIDGES. 


657 


mutual  relations  between  the  individual  crowns.  It  is  evident  that  as 
these  pieces  are  to  be  rigidly  joined  to  one  immovable  piece,  the  abut- 
ments must  be  so  shaped  as  to  permit  placing  them  when  so  joined.  The 
next  consideration  is,  therefore,  the  dressing  of  the  walls  of  the  abutment 
until  they  are  parallel  or  less  than  parallel,  for  it  is  also  evident  that  if 
the  distance  ^  ^  be  less  than  B  B  (Fig.  855,  1 ),  joined  cylinders  which 
shall  slip  over  A  A  will  not  be  in  contact  with  the  points  B  B ;  and 
this  latter  is  an  essential  condition  in  properly  adapted  abutment  crowns. 
(See  also  Fig.  856.)  With  post  crowns  it  is  evident  that  the  axis  of  the 
root-canal,  the  root-walls  covered  by  the  collar,  and  the  walls  of  the 
other  abutment  must  all  be  parallel  or  they  cannot  be  perfectly  set 
when  rigidly  united ;  the  lack  of  parallelism  is  shown  in  Fig.  855,  2. 

The  extent  of  the  lack  of  parallelism  between  the  axes  of  the  abut- 
ments are  noted  before  preparing  the  latter  for  the  reception  of  the 
abutment  crowns.      A    pair  of  accurate 
callipers  will  be  found    useful  to   make  ^^^'  ^'^^• 

measurements  to  determine  the  amount 
of  dressing  required.  Applied  first  to 
the  longest  distance  between  the  abut- 
ments, usually  at  the  necks  of  the  teeth, 
this  length  is  laid  upon  the  parts  of 
shortest  dilFerence.  The  portions  of  the 
tooth  necessary  to  equalize  the  lengths 
are  then  dressed  away.  Should  the  teeth 
diverge,  the  shortest  distance  is  first 
measured,  and  the  dressing  of  the  walls 
proceeded  with  as  before. 

To  allow  of  slight  aberrations  in  adjusting  it  is  usual  to  reduce  the 
walls  to  something  less  than  mutually  parallel  lines. 

The  dressing  or  shaping  of  the  walls  of  abutment  crowns  when  these 
latter  are  covered  with  enamel  is  readily  done  by  means  of  diamond 
disks  :  these  are  thin  disks  of  copper  charged  with  diamond  dust  (Fig. 
858). 

The  stump  corundum  wheel  having  a  brass  tire,  makes  the  wheel  safe- 
edge,  so  that  it  can  be  used  to  grind  off  the  sides  of  a  natural  crown,  as 
for  a  cap  crown,  without  risk  of  wounding  the  gum  (Fig.  857).     When 


Fig.  857. 


Fig.  858. 


Safe-edge  stump  corundum  wheel. 

the  sides  of  the  wheel  become  worn  by  use  the  edge  of  the  tire  can  be 

readily  turned  off  with  a  sharp  tool.     Size  of  wheel,  1  inch  diameter. 

Properly  adapted  corundum  wheels  may  also  be  used  for  the  purpose. 

The  safe-sided  diamond  disk  is  to  be  employed  where  a  space  is  to  be  cut 

42 


658 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


between  adjoining  teeth.  The  tooth  to  be  shaped  is  first  squared  on  four 
sides  by  means  of  disks,  and  given  a  slightly  pyramidal  form ;  the 
angles  of  the  pyramid  are  then  rounded  (Fig.  859). 

In  forming  the  retaining  slots  for  the  reception  of  abutment  bars, 
they  and  the  bar  itself  should  have  a  form  which  shall  prevent  either 
the  withdrawal  or  movement  of  the  bar  in  its  socket.  The  bar  is  to  be 
so  shaped  and  anchored  as  to  form  mechanically  part  of  the  abutment 
tooth.  It  is  obvious  that  cylindrical  or  prismatic  bars  would  have  by 
their  form  a  liability  to  be  withdrawn  if  the  bridge  or  its  abutment 
should  be  subjected  to  such  stress.    For  example,  see  Fig.  860.    Were  the 


Fig.  859. 


Fig.  860. 


861. 


Fig.  862. 


bars  of  this  suspension  tooth  made  of  cylindrical  or  prismatic  wires  the 
movements  of  the  abutment  teeth  through  the  force  of  mastication,  and 
also  the  stress  upon  the  bridge  tooth,  would  tend  to  strip  the  fillings  re- 
taining the  bar  from  the  latter.  Moreover,  a  cylindrical  bar  would,  when 
the  bridge  tooth  is  subjected  to  stress,  act  as  a  trunnion  upon  which  the 
bridge  is  swung,  and  the  bridge  tooth  would  rotate  upon  that  axis. 
Shaping  the  bar,  as  in  the  cut,  as  a  pyramid  having  its  base  in  the 
farthest  wall  of  the  abutment  cavity,  would  prevent,  first,  the  moving  of 
the  abutment  teeth  away  from  the  bar ;  second,  would  prevent  the  bar 
from  turning  upon  its  axis. 

The  cavity  in  the  tooth  it  readily  formed  by  means  of  dentate  fissure 
burs :  these  are  employed  to  make  the  slot,  which  is  then  enlarged  and 
shaped  with  burs  of  the  inverted  cone  pattern.  In  many 
cases  cavities  are  already  existent,  which  are  enlarged  to 
the  proper  dimensions  and  given  the  form  seen  in  Figs.  860 
and  862.  It  is  advisable,  where  possible,  to  have  the  edges 
of  such  cavities  extend  laterally  to  an  extent  which  shall 
admit  of  ready  cleansing  by  means  of  the  tooth-brush. 
Cavities  much  larger  than  the  proper  size  of  a  retaining  bar  receive 
a  preliminary  filling  which  is  firmly  anchored  in  the  tooth,  and  the 
slot  for  the  bar  is  cut  and  shaped  in  this  filling.  Indeed,  this  is  an 
excellent  practice  in  all  cases  of  bar  anchorage — the  covering  of  the 
walls  by  filling  material  and  the  finishing  of  the  margins  of  the  same 
previous  to  placing  the  retaining  filling  about  the  bar.  It  is  the  only 
method  by  which  the  operator  is  assured  that  the  essential  portion  of  the 
filling  is,  as  it  should  be,  in  absolute  contact  with  the  cavity- walls. 
Many  operators  have  an  unconquerable  objection  toward  the  cutting  of 
cavities  in  non-carious  teeth  to  serve  as  a  base  of  retention  for  a  bridge. 
Others,  recognizing  the  difficulty  of  keeping  the  edges  of  retaining  fillings 
perfectly  clear  of  fermenting  deposits,  prefer  to  dispense  with  this  means 
of  retention  entirely.  Occasionally  teeth  have  been  implanted  under 
favorable  conditions  to  serve  as  abutments  for  a  dental  brido-e. 


CLASSIFICATION  OF  BRIDGES.  659 

In  preparing  the  abutments  for  removable  bridges  they  are  to  be 
formed  with  the  great  primary  consideration  of  the  adjustment  of  a  basal 
fixture  which  shall  be  perfectly  adapted  to  the  abutment,  protecting 
effectually  against  the  ingress  of  pathogenic  material,  covering  com- 
pletely the  tooth-structure,  and  immovably  attached  to  it. 

In  many  cases  removable  bridges  are  placed  over  abutments  having 
inclined  positions  ;  the  attempt  at  securing  mutually  parallel  walls  of 
the  abutments  is  a  secondary  consideration.  The  abutment  is  so  shaped 
that  a  single  crown  may  be  adapted  perfectly  ;  the  abutment  crowns  of 
the  removable  bridge  are  then  cut  away  until  they  may  both  be  placed  or 
removed  together  in  a  plaster  impression. 

Requisites  of  a  Correct  Bridge. — The  first  requisite  is  that  a  dental 
bridge  must  be  regarded  as  a  prosthetic  appliance  in  its  fullest  sense  :  it 
should  restore  as  nearly  as  possible  lost  form,  appearance,  and  function. 
It  should  therefore  restore  the  general  contour  lost  through  the  loss  of 
the  teeth,  and  reproduce  the  forms  of  the  natural  crowns.  The  pieces 
should  be  constructed  for  aesthetic  effect  with  the  same  care  as  with  a 
plate  denture.  The  teeth  should  be  selected  with  the  same  regard  to 
their  proper  sizes,  shapes,  and  colors  as  with  plate  dentures.  The  same 
care  is  to  be  exercised  in  accurately  adapting  crowns  as  when  these  fix- 
tures are  made  and  applied  as  single  crowns.  These  details  are  frequently 
ignored  or  deemed  of  minor  importance — a  view  to  which  the  student 
should  by  no  means  subscribe.  The  masticating  surfaces  are  to  be  so 
formed  that  they  will  occlude  perfectly  with  the  antagonizing  teeth ; 
moreover,  so  that  they  shall  effectively  perform  the  work  of  actual  mas- 
tication to  an  extent  commensurate  with  the  resistance  of  the  abutments. 

It  is  unwise  to  make  the  restoration  in  this  particular  too  complete ; 
that  is,  by  restoring  full  cusp  lengths  and  full  occluding  surfaces,  as 
would  be  the  case  were  the  Bonwill  articulator  used  and  the  teeth  perfect 
anatomical  representatives  of  the  lost  organs.  The  occluding  surfaces  are 
given  a  smaller  area,  and  the  cusps  made  shorter  than  with  the  natural 
teeth,  so  that  the  vertical  and  lateral  forces  upon  the  abutments  are 
lessened  to  the  required  degree.  When  the  jaws  are  in  normal  closure, 
however,  the  occlusion  should  be  perfectly  accurate  or  else  the  useful- 
ness of  the  piece  is  lessened. 

If  possible,  every  portion  of  the  bridge  and  abutments  above  the  gum 
line  should  be  easily  accessible  to  the  bristles  of  a  tooth-brush.  Tooth- 
substance  should  form  no  wall  of  a  pocket  inaccessible  to  the  same  im- 
plement. The  bridge  should  cover  and  seal  such  surfaces.  It  should  be 
sufficiently  rigid  in  all  its  parts,  and  be  so  firmly  attached  to  its  abut- 
ments that  abutments,  bridge,  and  all  its  parts  are  a  rigid  piece,  having 
not  the  least  movement  except  as  a  single  piece.  It  is  essential  that  the 
abutments  or  their  crowns  have  no  movement  upon  one  another.  This 
necessitates  that  each  crown  shall  be  in  itself  sufficiently  rigid  to  resist  any 
change  of  form  through  the  stress  of  mastication.  It  is  not  alone  neces- 
sary that  a  crown  shall  fit  an  abutment  perfectly  ;  it  must  continue  to  do  so. 

As  stated  earlier  in  this  chapter,  there  should  be  in  the  placing  of  a 
bridge  a  diminution  rather  than  an  increase  of  the  opportunities  for  dis- 
ease process  arising.  All  edges  which  come  in  contact  with  the  soft 
tissues  should  be  smoothed  and  rounded.  Every  surface  of  the  bridge 
should  be  free  from  inequalities  or  mechanical  blemish  of  any  kind. 


660 


AN  ASSEMBLAGE  OF   UNITED   CROWNS. 


Selection  of  the  Variety  of  Bridge. — The  many  advantages  afforded 
by  bridges  which  may  be  removed  with  comparative  ease  over  those 
irremovably  attached  to  their  abutments  will  no  doubt  lessen  the  appli- 
cation of  the  latter  devices.  Definite  conditions  must  be  present,  how- 
ever, to  indicate  the  application  of  the  class  first  named.  Their  great 
field  of  usefulness  is  where  the  abutment  teeth  overhang  or  incline  toward 
one  another  to  such  an  extent  that  it  is  inadvisable  to  reduce  their  walls 
to  parallel  lines,  as  in  Fig.  863. 

Fig.  863. 


Where  possible  it  is  preferable  to  have  the  abutment  crowns  of  barrel 
or  collar  crowns,  rather  than  depend  upon  bar  anchorage.  Devices  which 
embrace  the  anterior  teeth  are  constructed  so  that  the  metallic  portions  of 
the  fixture  are  not  exposed  through  the  movements  of  the  lip.  Appli- 
ances which  include  what  are  known  as  partial  caps  are  to  form  a  second 
choice. 

When  post  crowns  form  the  abutment  pieces  they  should  be  mounted 
with  collars  attached  either  to  the  crowns  or  placed  over  the  root  itself. 

Any  dummy  device  which  is  not  rigidly  supported  beyond  the  last 


Fig.  864. 


Fig.  865. 


crowns  is  to  be  viewed  as  mechanic- 
ally faulty,  and  not  employed  except 
under  exceptional  circumstances. 
Fiff.  864  exhibits  a  mild  form  of 
this  defective  type ;  Fig.  865  an 
exaggerated  one.  The  extreme  justifiable  limit  of  bridge-work  is  seen 
in  Fig.  866. 

It  is  to  be  remembered  that  with  an  increase  in  the  number  of  pieces 
composing  a  bridge  there  is  a  corresponding  increase  of  difficulty  in  its 
construction.  To  properly  make  and  adjust  such  a  bridge  as  is  shown  in 
Fig.  866  will  tax  the  skill  of  the  finished  and  conscientious  operator. 

The  several  devices  figured  in  this  chapter  are  to  be  regarded  as 
representatives  of  classes.  The  ingenuity  and  developing  skill  of  the 
operator  will  suggest  modifications  which  special  cases  may  require,  and 
prompt  him  to  a  judicious  application  of  features  of  several  types  in 
pieces  he  may  be  called  upon  to  construct. 

Fixed  bridges  are  of  several  types,  the  simplest  that  having  terminal 


THE  MANUFACTURE  OF  DENTAL  BRIDGES.  661 

abutments  of  two  crowrivS.    The  first  class  of  these  is  for  the  replacement 
of  two  or  more  side  teeth ;    the  second,  the  bulkhead  form  of  bridge  for 

Fig.  866. 


the  replacement  of  the  incisors  ;  next,  bridges  having  three,  then  four 
abutments.  Another  class  are  those  having  some  break  in  the  continuity 
of  the  bridge  arch,  owing  to  the  presence  of  a  natural  tooth  which  forms 
no  part  of  the  bridge ;  the  next,  the  class  of  appliance  known  as  wing  or 
extension  bridge ;  finally,  the  removable  bridges,  which  are  subdivided 
into  several  varieties. 

The  Manufactube  of  Dental  Bridges. 

There  are  involved  in  the  making  of  a  bridge  three  sets  of  manipu- 
lations :  first,  the  making  of  the  abutment  crowns ;  second,  the  manu- 
facture of  the  intervening  dummies ;  and,  third,  the  uniting  of  the  sev- 
eral parts  into  one  rigid,  highly  finished  piece.  From  beginning  to  end 
it  includes  a  series  of  small  but  important  details.  In  the  degree  that 
care  and  attention  are  devoted  to  these  minutiae  will  be  the  accuracy  of 
fit  and  finish  of  the  completed  bridge  ;  neglect  of  them  may  be  followed 
by  blemish  or  even  by  disaster. 

Esthetic  considerations  are  too  frequently  ignored  in  this  class  of 
work,  but  they  are  equally  important  in  this  as  in  any  prosthetic  opera- 
tion. The  completed  piece  should  present  a  restoration  as  nearly  as 
possible  of  the  forms,  color,  size,  and  positions  of  the  natural  organs, 
and  should  be  so  articulated  as  to  restore  the  lost  masticating  surfaces. 

Unnecessary  exposure  of  gold  is  to  be  avoided,  and  yet  the  several 
porcelain  pieces  are  to  be  so  guarded  that  they  serve  merely  for  the 
restoration  of  appearances,  receiving  themselves  no  direct  force,  the  latter 
bearing  only  upon  masticating  surfaces  of  gold.  By  this  means  fracture 
of  the  porcelain  becomes  a  remote  possibility. 

The  most  usual  form  of  bridge  is  that  of  two-collar  crowns,  carrying 
one  or  more  dummies.  A  typical  case  is  selected  for  example :  A 
patient  has  lost  the  two  bicuspids,  first  and  second  molar  of  the  side. 
The  cuspid  and  third  molar  are  the  seat  of  extensive  caries.  These 
teeth  are  treated  and  shaped  as  described  under  the  head  of  preparation 
of  roots  given  the  forms  seen  in  Fig.  867. 

A  collar  crown  is  fitted  to  the  cuspid ;  a  hollow  gold  crown  to  the 
molar.  (The  methods  of  constructing  these  crowns  will  be  found  in 
Chapter  XVIII.)    Not  uncommonly  the  latter  crown  is  made  of  too  thin 


662 


^.V  ASSEMBLAGE  OF  UNITED   CROWNS 


metal ;  all  barrel  crowns  serving  as  abutment  crowns  of  bridges  must  be 
rigid  enough  to  prevent  any  change  of  form  arising  from  the  stress  upon 
it  received  through  the  body  of  the  bridge.     Not  infrequently  crowns 


Fig 


Fig.  868. 


made  of  thin  gold  are  seen  to  break  or  to  become  bent  under  this  strain. 
All  of  the  soldering  on  these  crowns  should  be  done  with  22-carat 
solder. 

The  crowns  when  made  and  carefully  finished  are  adjusted  to  their 
respective  bases  ;  a  wax-bite  taken  of  the  entire  side ;  a  wax  impression 
of  the  antagonizing  teeth  is  made,  carefully  poured,  and  the  plaster  teeth 
varnished  with  shellac.  Succeeding  this,  a  plaster  impression  is  taken 
of  the  teeth  and  gum,  in  which,  if  the  abutments  have  been  properly 
shaped,  the  crowns  should  be  withdrawn.  If  not,  it  is  better  to  perform 
such  trimming  operations  as  will  permit  the  withdrawal  of  both  crowns 
in  the  impression. 

The  plaster  impression  is  varnished  and  a  plaster  model  made.  When 

separated  the  wax-bite  is  placed  on  the 
model  and  tlie  cast  of  the  inferior  teeth 
carefully  set  in  position  and  mounted  in 
the  articulator. 

Porcelain  facings  are  selected  the  color 
of  the  cuspid  porcelain  (Fig.  868).  The 
necks  of  the  facings  should  just  touch  the 
gum,  their  cutting  edges  to  be  in  contact 
with   the  antagonizing  teeth. 

The  following  description  is  that  of  the 
method  usually  practised  by  the  writer ;  it 
is  somewhat  more  tedious  than  those  gen- 
erally followed,  but  the  increased  accuracy 
of  articulation  and  better  protection  of  the 
porcelain  recommend  its  employment.  The 
general  process  may  be  applied  to  the  making  of  the  masticating  dum- 
mies of  any  bridge.     In  fact,  the  making  of  a  bridge  consists  essentially 


THE  MANUFACTURE  OF  DENTAL  BRIDGES. 


663 


in  constructing  two  or  more  crowns  of  the  types  described  in  Chapter 
XVIII.,  and  uniting  them  with  the  dummies  in  such  a  manner  as  to 
form  a  rigid   fixture. 

Each  facing  is  ground  and  fitted  to  the  models  as  though  a  plain  tooth 
were  being  fitted  to  a  plate,  its  upper  edge  just  resting  upon  the  gum. 
The  cut  surface  of  the  porcelain  is  now  smoothed  and  polished.  The  oc- 
cluding edge  of  the  facing  is  to  be  ground  to  within  less  than  one-sixteenth 
of  an  inch  of  contact  with  the  antagonizing  teeth,  and  bevelled  toward 


Fig.  869. 


Fig.  871. 


Fig.  870. 


its  outer  edge,  the  bevels  to  be  long  (Fig.  870).  Stays  of  pure  gold  or  of 
crown  metal  are  to  be  fitted  to  the  facings,  extending  from  the  outer  edge 
of  the  occlusal  portion  to  near  the  gum  line.  The  facings  are  arranged  in 
position  on  the  model,  and  held  by  means  of  wax  melted  about  their 
bases.  The  surface  of  the  latter  and  that  of  the  antagonizing  model  are 
to  be  varnished.  A  batter  of  soft  plaster  is  built  against  the  stays  and 
above  the  cutting  edges  of  the  teeth ;  it  is  to  extend  from  abutment  to 
abutment,  and  be  broader  than  the  masticating  surfaces  of  the  proposed 
dummies.  While  the  plaster  is  still  soft  the  teeth  of  the  antagonizing 
model  are  brought  into  occlusion.  As  soon  as  the  plaster  has  set  its 
surface  is  scraped  down  uniformly  to  about  the  thickness  of  No.  30 
plate.  At  its  outer  edge  it  is  scraped  away  until  the  edge  of  each 
dummy  stay  is  exposed.  The  width  of  the  plaster  block  is  to  represent 
the  area  of  the  masticating  surface  of  the  dummies,  and  is  cut  to  the 
desired  width.  Saw-cuts  are  made  marking  the  individual  teeth.  The 
irregular  plaster  surface  is  now  carved  into  cusps  and  sulci,  according 
to  the  elevations  and  depressions  made  in  the  plaster  by  the  tips  of  the 
antagonizing  teeth.     (See  Fig.  871.) 

An  anatomically  correct  occlusion  may  be  moulded  by  mounting  the 
models  in  a  Bonwill  articulator,  and  carving  cusps  and  sulci  in  the  plas- 
ter, so  that,  when  the  movable  jaw  of  the  articulator  is  moved,  every 
tooth  of  the  side  is  seen  to  be  in  occlusion.  This  premises,  however,  that 
full  models  of  each  jaw  be  mounted  in  the  articulator. 

The  plaster  block  is  now  varnished,  and  when  dry  a  die  of  Babbitt 
metal  is  made  of  it.  A  cap  of  No.  30  pure  gold  is  to  be  swaged,  fitting 
the  surface  of  the  plaster  and  joining,  but  not  overlapping,  the  abutment 
crowns.  (See  Fig.  820.)  The  piece  so  formed  is  placed  on  the  die  and 
divided  into  pieces  at  the   grooves  marking  the   individual  teeth   by 


664 


AN  ASSEMBLAGE  OF   UNITED   CROWNS. 


Fig.  872. 


means  of  a  fine  saw-blade.  The  caps  are  boiled  in  acid  solution,  and 
are  filled  flush  by  melting  22-carat  solder  in  them.  The  plaster  holding 
the  facings  to  the  model  is  removed  and  wax  substituted.  The  outer  edges 
of  the  caps  are  ground  or  filed,  so  that  they  are  in  accurate  contact  with 
the  edges  of  the  stays  and  occlude  accurately  (Fig.  869).  Their  lateral 
edges  are  dressed  until  they  join  one  another  closely  and  there  is  an 
accurate  joint  with  the  abutment  crowns.  The  several  pieces  (caps  and 
facings)  are  boiled  in  the  acid  solution.  A  thin  layer  of  wax  is  placed 
on  the  model  between  the  abutments,  just  sufficient  to  hold  the  facings 
in  position ;  the  caps  are  set  on  the  facings  and  attached  by  means  of 
adhesive  wax ;  while  the  latter  is  still  soft  the  caps  are  placed  in  their 
correct  positions  in  relation  with  each  other  and  with  the  antagonizing 
teeth.  Each  facing  with  its  cap  attached  is  removed  from  the  model. 
A  triangular  strip  of  mica  may  be  attached  to  the  sides  of  each,  as 
recommended  by  Dr.  R.  W.  Starr.  The  pieces  are  then  invested  in 
a  common  investment  (Fig.  872).      A  number  of  pieces  of  24-carat 

gold,  having  decreasing  width,  are  cut ;  all 
the  surfaces  are  covered  with  borax.  The 
depression  enclosed  by  the  mica  strips  and 
cap  is  filled  with  these  pieces,  and  the  sur- 
faces so  made  are  covered  M^ell  with  22-carat 
solder.  The  investment  is  heated  on  a  fur- 
nace, and  next  upon  a  charcoal  bed,  using  a 
blowpipe  flame  directed  against  the  back  of 
the  investment.  When  the  entire  investment 
is  heated  bright  red,  the  solder  beginning  to 
fuse  through  the  transmitted  heat,  a  fine 
blowpipe  flame  is  directed  against  the  gold 
until  the  solder  flows  freely,  adding  more 
and  more  of  the  latter  until  each  depression 
is  filled,  and  giving  a  smooth-surfaced  g:old 
block.  When  cold  break  away  the  investment  and  boil  in  the 
solution. 

The  method  described  will  furnish  the  most  accurate  occlusion 
a  minimum  exposure  of  gold,  together  with  perfect  protection  of  the 
porcelain  and  a  minimum  risk  of  checking  the  facings  during  soldering. 
A  similar  method  is  that  of  the  Hollingsworth  system. 

To  Mahe  the  Grinding  Surface  of  a  Bridge  in  One  Continuous  Piece. 
— After  having  crowned  the  teeth  for  the  attachment  of  the  bridge,  take 


acid 


and 


Fig.  873. 


ar^bite  in  modelling  compound,  remove  the  compound,  place  the  crowns 
in  their  impressions,  make  a   cast  of  sand  and   plaster,  and  place  on 


THE  MANUFACTURE   OF  DENTAL  BRIDGES. 


665 


an  articulator ;  now  put  moldine  between  the  abutments  instead  of 
wax,  and  get  the  articulation  with  cusp-buttons  the  same  as  for 
plate  teeth  (Fig.  873).  Then  to  reinove  the  buttons  Avithout  destroy- 
ing the  articulation,  make  a  cup  by  pouring  Melotte's  metal,  as  cool 
as  it  will  flow,  on  the  face  of  the  cusp-buttons.  Heat  the  pouring  lip 
of  the  ladle  and  use  it  to  smooth  out  the  half-solidified  metal,  as 
with  a  soldering  iron  (Fig.  874).  Then  place  a  thin  coating  of  mold- 
ine upon  the  moulding  plate.  Remove  the  cup  from  the  articulator 
with  the  cusp-buttons  in  place  (Fig.   874,  A).     Transfer  the  cusjas  by 

Fig.  874. 


inverting  the  moulding  plate  (Fig.  875),  and  turn  the  cusp  buttons 
out  upon  the  moldine  on  the  plate  with  the  grinding-surface  up  (Fig. 
875),  and  they  will  occupy  the  same  relative  positions  as  when  on 
the  articulator. 

Now  place  the  large  rubber  ring  around  the  buttons  on  the  plate,  and 
proceed  to  make  a  die  with  Melotte's  metal,  as  before  described  (Fig. 
876).      When  cool,  remove  the  buttons   and  coat  the  face  of  the  die 


Fig.  875. 


Fig.  876. 


with  whiting 


Invert  the  die  and  raise  the  rubber  ring  sufficiently  high 
on  it,  and  niake  a  counter-die  with  the  same  metal  by  pouring  as  cool  as 
possible  (Fig.  877). 

This  gives  the  male  and  female  dies  with  which  to  swage  the  contin- 
uous grinding-surfaces.     Then  proceed  to  swage  the  gold  plate  in  one 


Fig.  877. 


Fig.  878. 


Fig.  879. 


piece  (Fig.  878),  annealing  as  often  as  necessary.  Trim  oflP  the  sur- 
plus plate  (Fig.  878),  and  place  in  position  on  the  articulator.  Cut 
the  cusps  out  on   the    buccal    face    to    avoid    showing   the   gold   (Fig. 


me 


AN  ASSEMBLAGE  OF   UNITED   CROWNS. 


879),  grind  the  porcelain  facings  to  fit  the  cusps,  and  back  with  gold, 
No.  34  or  36,  letting  the  gold  come  to  the  cutting  edge,  the  same  as  in  a 
single  crown  as  before  described. 

If  there  is  a  space  between  the  cutting  edge  and  the  porcelain,  place 
a  little  wax  in  the  joint  to  keep  out  the  plaster  investment,  invest, 
remove  the  wax  from  between  the  joints,  flux,  and  solder. 

Pacing-s  for  Making-  AU-g-old  Bridge. — If  it  is  desired  to  make  an 
all-gold  bridge,  select  the  proper  facings  from  the  set,  make  a  die  of 

Fig.  880. 


Melotte's  metal,  and  swage  up,  the  same  as  in  the  continuous  bridge 
before  described,  and  mount  gold  facings  in  place  of  porcelain. 


Fig.  881. 


The  usual  method  of  forming  the  dummies  is  by  the  brass  or  steel 
dies  or  plates  to  be  had  from  dealers  in  dental  supplies  (Fig.  880). 


THE  MANUFACTURE  OF  DENTAL  BRIDGES. 


667 


Appropriate  forms  of  crown  caps  are  selected,  using  small  leaden  hubs 
(the  plate  for  forming  the  hubs  is  shown  in  Fig.  881) :  the  latter  are 


Fig.  882. 


driven  into  the  depression  of  the  die-plate,  forming  small  lead  dies.     A 

piece  of  pure  gold,  No.  30  or  31,  is  pressed  into  the  depression  the  lead 

die  set  over  it,  and  a  cap  is  swaged, 

which  is  then    filled   with    22-carat  Fig. 

solder. 

The  under  surfaces  of  these  filled 
caps  are  ground  flat  on  the  side  of  a 
corundum  wheel ;  the  facing,  which 
has  had  a  backing  adjusted,  is 
ground  square,  making  a  close  joint 
with  the  cut  surface  of  the  metal 
cap,  their    outer    edges    in   a    line 

Fig.  883. 


(Fig.  883).  They  are  next  adjusted  to  occlusion  as  described,  invested, 
and  soldered  after  the  same  manner  (Fig.  884). 

When  the  steel  dies  (Fig.  882)  are  used  the  counter-die  is  formed  by 
driving  them  into  a  block  of  soft  lead. 

Another  method  occasionally  practised  is  as  follows :  Instead  of 
separating  the  swaged  cap-piece  into  several  teeth,  it  is  filled  flush 
with   solder,    ground   flat   at   the  parts    which   are    to    rest    upon    the 


668  AN  ASSEMBLAGE  OF   UNITED   CROWNS 

porcelain  facings.  The  latter  are  backed  and  ground  to  positions. 
Next,  waxed  to  place,  they  are  invested,  the  space  beneath  the  caps 
filled  with  pieces  of  24-carat  plate,  and  covered  with  solder ;  the  piece  is 
heated  and  soldered.  The  contraction  of  the  large  mass  of  solder  tends 
to  bend  or  distort  the  gold  cap,  and  it  increases  the  danger  of  fracturing 
the  porcelain. 

After  making  the  individual  dummies  it  is  advisable  to  unite  them 
in  one  piece  before  attaching  to  the  abutment  crowns.  They  are  all 
adjusted  to  the  plaster  models  and  a  stiff  wire  laid  along  their  under 
surfaces,  which  are  then  covered  by  adhesive  wax  to  rigidly  maintain  the 
relative  positions  of  the  pieces.  They  are  then  invested,  and  united  to 
one  another  with  20-carat  solder.  When  cool  the  piece  is  smoothed  and 
buffed.  This  operation  may  be  more  perfectly  done  at  this  stage  than  in 
the  finished  piece. 

Many  operators,  having  made  the  model  of  investing  material  instead 
of  plaster,  now  set  the  block  in  position,  wet  the  model,  and  cover  the 
block  and  abutment  crowns  with  more  of  the  investing  material,  leav- 
ing the  joints  to  be  soldered  exposed.  The  case,  dried  carefully  to  avoid 
separation  of  the  new  from  the  old  investment,  is  heated  and  the  dummy 
block  united  to  the  abutment  crowns  with  20-carat  solder. 

Greater  accuracy  is  assured  by  an  adjustment  of  the  pieces  in  the 
mouth  before   uniting  them. 

The  abutment  crowns  are  removed,  and,  with  the  dummy  block, 
boiled  in  the  pickle,  washed,  and  dried.  The  crowns  placed  in  proper 
positions  on  their  bases,  a  block  of  soft  wax  is  attached  to  the  base  of 

Fig.  885. 


the  dummies,  and  it  is  pressed  to  its  proper  position  in  the  mouth,  test- 
ing the  occlusion.  A  plaster  impression  is  now  taken,  covering  the 
bridge  pieces  just  enough  to  secure  their  withdrawal  in  the  impression. 


THE  MANUFACTURE  OF  DENTAL  BRIDGES.  669 

Should  the  several  pieces  not  be  removed  in  the  impressions,  they  are 
detached  separately  and  set  in  their  correct  position.     (See  Fig.  885.) 

The  plaster  of  the  impression  is  scraped  away  until  it  serves  merely 
as  a  guide  and  to  retain  the  pieces  in  their  correct  relative  positions 
(Fig.  885).  The  wax  underlying  the  dummies  will  be  withdrawn  in  the 
impression  :  it  is  to  be  permitted  to  remain,  so  that  the  investing  material 
to  be  poured  into  the  impression  will  not  enter  the  soldering  space.  The 
plaster  surfaces  are  varnished  and  a  cast  poured  of  investing  material ; 
when  the  latter  is  hard  the  impression  is  cut  away.  Additional  invest- 
ment material  is  placed  to  protect  the  porcelain  and  the  solder  of  the 
body  of  the  bridge,  but  leaving  exposed  entire  the  joints  between  the 
latter  and  the  abutment  crowns.  A  sufficient  amount  of  20-carat  solder 
— or,  unless  the  operator  be  an  expert,  18-carat  solder — is  placed  along 
the  joint  to  be  soldered.  The  investment  is  to  be  first  thoroughly  dried, 
and  the  heat  increased  gradually  until  it  is  red  hot.  The  injunction  to 
heat  slowly  is  given,  as  not  infrequently  too  rapid  a  heating  will  prevent 
the  gradual  escape  of  steam  from  beneath  barrel  crowns,  and  may  lead 
to  their  displacement. 

When  the  case  is  at  a  uniform  red  heat  turn  the  fine  blowpipe  flame 
upon  the  joint  and  flow  the  solder,  adding  more  of  the  latter  if  neces- 
sary to  fill  the  joint  flush.  The  investment  should  be  permitted  to  cool 
slowly.  When  cold  it  is  boiled  in  a  strong  acid  solution  and  the  joints 
made  smooth  by  means  of  fine  files  and  emery-cloth  No.  00,  The  piece 
is  to  be  so  finished  that  there  shall  be  no  imperfections  at  any  part  of  its 
surface.  The  finish  should  be  of  such  a  type  that  an  expert  goldsmith 
would  approve  of  it ;  any  lower  standard  than  this  is  to  be  regarded  as 
a  faulty  and  imperfect  finish  for  a  crown  or  bridge  piece. 

Dr.  M.  W,  Hollingsworth  of  Philadelphia  has  furnished  a  description 
of  a  method  of  casting  the  metallic  body  of  bridge  pieces  devised  and 
followed  by  him  for  several  years. 

The  abutment  crowns  are  made  and  adjusted  to  their  bases ;  a  bite 
and  a  plaster  impression  are  taken,  a  model  of  sand  and  plaster  formed, 
and  an  articulating  model  mounted.  Appropriate  porcelain  facings  are 
selected  and  adapted,  the  cutting  edges  of  the  facings  to  be  short  of 
occlusion  sufficiently  to  admit  the  usual  thickness  of  protective  covering 
of  gold.  The  palatal  surfaces  of  the  facings  are  bevelled  away  from  the 
pins  on  all  sides.  Stays  of  24-carat  gold 
No.  27   are  adapted ;  the  facings  are  in-  Fig.  886. 

vested  and  soldered  to  the  pins.  When 
cool  the  projecting  ends  of  the  pins  are 
ground  away. 

BetM-een  the  abutment  crowns  on  the 
model  a  mass  of  softened  wax  is  placed  : 
it  is  preferable  to  employ  one  of  the  wax 
compounds,  wax  and  gutta-percha,  or  wax 
and  paraffin.  The  surfaces  to  be  covered 
by  the  wax  are  moistened  to  prevent  their 
adhesion  to  crowns  or  model. 

While  the  mass  is  soft  the  jaws  of  the  articulator  are  brought 
together  and  the  facings  set  in  their  proper  positions,  the  facings  having 
also  been  moistened.     When  the  wax  mass  is  hard  all  excess  is  trimmed 


BRIDGC  CASTING 


670 


AN  ASSEMBLAGE   OF   UNITED   CROWNS. 


away,  and  it  is  carved  into  the  form  of  the  future  bridge  body,  special 
care  being  bestowed  upon  the  accuracy  of  occlusion  (Fig.  886).  The 
wax  mass,  thoroughly  chilled,  is  then  lifted  from  the  model  and  each 
facing  detached  and  set  aside.  At  one  extremity  of  the  wax  pattern  a 
cylinder  of  wax,  one-eighth  of  an  inch  by  one-fourth  of  an  inch,  is 
cemented. 

In  a  shallow  sheet-iron  tray  having  a  handle  a  mixture  of  marble- 
dust  and  plaster  investment,  mixed  thin,  is  poured.  At  the  square 
portions  of  the  tray  the  wax  pattern  is  set,  with  the  projecting  tongue 
on  a  level  with  the  surface  of  the  investment ;  the  investing  material  is 
built  over  the  wax  pattern,  covering  it  to  a  depth  of  about  half  an  inch, 
the  small  projection  to  have  its  end  exposed,  as  shown  in  Fig.  887. 

Fig.  887. 


In  the  flat  section  of  the  investment  a  concavity  is  carved  to  serve 
as  a  melting-pot.  Running  from  this  depression,  and  joining  the  wax 
terminal  of  the  bridge  pattern,  a  gutter  is  cut.  The  investment  about 
the  wax  terminal  is  cut  so  that  it  has  a  bell  mouth ;  this  is  to  permit  the 
ready  entrance  of  the  molten  gold  to  the  mould.  The  entire  piece  is 
brushed  to  free  it  of  any  loose  fragments  of  sand.  The  tray  and  invest- 
ment are  now  heated  until  all  of  the  wax  pattern  is  burned  out.  An 
excess  of  22-carat  gold  is  placed  in  the  melting-pan  (the  depression), 
and  a  large  blowpipe  flame  directed  against  the  gold  and  investment. 
As  the  success  of  casting  will  depend  largely  upon  the  fluidity  of  the 
gold  at  the  moment  of  pouring  and  the  weight  of  its  column,  the  heat 
is  maintained  until  the  gold  is  freely  molten,  when  by  a  turn  of  the 
hand  the  pan  is  inclined,  permitting  the  gold  to  run  from  the  melting- 
pot  into  the  mould,  filling  it  to  the  mouth.  When  cool  the  gate  cylinder 
is  sawn  ofl^"  and  the  bridge  body  accurately  fitted  to  position  between  the 
abutments. 

The  outer  wall  of  the  bridge  body  is  marked  into  depressions  into 
which  the  facings  fit  accurately.  The  pieces  are  boiled  in  the  sulphuric- 
acid  solution,  dried,  and  the  facings  attached  in  position  by  means  of 


THE  MANUFACTURE  OF  DENTAL  BRIDGES. 


671 


Fig 


wax  flux  melted  along  the  joint  lines.  The  piece  is  invested,  having  the 
investment  thin  over  the  facings  and  articulatory  faces  of  the  bridge. 
At  the  joints,  between  the  stays  and  bridge,  at  the  necks  of  the  facings, 
small  pieces  of  18-carat  solder  are  placed,  and  the  investment  heated 
from  the  outer  side  until  the  solder  flows,  uniting  stays  and  bridge  per- 
fectly. When  cool  the  piece  is  boiled  in  acid,  smoothed,  polished,  then 
adjusted  to  position  on  the  model.  More  investment  is  added,  and  the 
bridge  is  united  to  the  abutment  crowns  as  before  described. 

•  The  Bulkhead  Bridge. — Another  class  of  cases  frequently  seen  are 
comprised  in  those  for  the  replacement  of  the  superior  incisors,  the 
anchorages  being  the  roots  of  the  cuspids.  As  a  rule,  it  is  necessary  in 
order  to  gain  adequate  mechanical  support 
for  such  a  piece  to  remove  the  crowns  of 
the  cuspids.  For  the  correct  application  of 
a  bridge  there  should  be  so  little  absorption 
of  the  alveolar  plate,  so  slight  a  loss  of 
fulness  of  the  gum,  as  to  permit  the  adapta- 
tion of  plain  teeth  of  the  proper  size  and  form. 

In  the  event  of  it  being  necessary  to  employ  gum  teeth  a  fixed  bridge 
is  contraindicated,  but  it  is  still  quite  possible  to  adjust  a  removable 
piece  of  a  type  to  be  described  later. 

It  is  possible  to  form  the  abutment  pieces  of  partial  cylinders  attached 
to  the  abutment  teeth  (Fig.  888),  but  this  principle,  as  above  implied, 
is  faulty  both  mechanically  and  hygienically.  Should  it  be  decided 
to  utilize  this  type  of  anchorage,  it  is  advisable  to  form  the  shell 
anchorage  after  Dr.  Mellotte's  method. 

"  It  is  necessary  to  first  reduce  all  of  the  mesial  and  distal  walls  of  the 
teeth  to  parallel  lines,  so  that  pieces  which  pass  over  the  crowns  will  be 
in  close  apposition  with  the  necks  of  the  teeth. 

"  As  there  may  be  grounds  for  objection  to  cutting  off  sound  teeth,  a 
shoulder  cut  on  the  lingual  portion  of  the  cuspid,  and  suitably  shaping 
its  side  to  permit  a  close  fitting  of  the  collar  just  under  the  free  margin 
of  the  gum,  will  avoid  that  necessity.  A  narrow  strip  of  pattern  tin, 
bent  tight  around  the  tooth  neck  and  cut  through  with  a  knife  at  the 


lap  on  the  labial  surface,  will  serve  as  a  measure  for  the  length  of  a 
strip  of  22-carat  gold  plate,  No.  29  thick,  and  as  wide  as  the  length  of 
the  distal  side  of  the  cuspid.  The  ends  of  the  gold  are  then  squared, 
and  with  round-nosed  pliers  brought  evenly  together  to  be  held  in  flush 
contact  by  the  soldering-clamp  shown  in  Fig.  889.     The  soldered  collar. 


672 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


Fig.  890. 


Fig.  891. 


with  its  joint  side  inward,  is  then  adjusted  on  the  tooth  as  accurately  as 
possible,  giving  slight  blows  with  a  mallet  until  the  collar  touches  the 
gum,  when  it  should  be  marked  to  indicate  the  necessary  trimming  to 
conform  it  to  the  gum  outline.  After  it  has  been  thus  trimmed, 
the  edges  bevelled,  the  labial  part  shaped  with  contouring  pliers,  the 
labial  part  cut  down  to  about  one-tenth  of  an  inch  in  width,  the  collar 

is  again  driven  on,  and  will  appear 
as  seen  in  Fig.  890.  A  stump  corun- 
dum wheel  is  then  used  to  grind  a 
shoulder  on  the  lingual  surface  of  the 
tooth,  grinding  also  the  edges  of  the 
collar  flush  with  the  shoulder.  The 
collar  is  again  removed,  and  a  piece 
of  thin  platinum  plate,  about  No.  32, 
sufficient  to  cover  the  lingual  surface  of  the  tooth,  is  caught  on  the  lin- 
gual edge  of  the  collar  by  the  least  bit  of  solder,  and  all  put  in  place 
on  the  cuspid.  (See  Fig.  891,  A.)  The  platinum  should  now  be  bur- 
nished on  the  shoulder  and  over  the  tooth  and  collar  to  the  extent  shown 
by  the  lines  in  Fig.  891.  After  trimming  to  those  lines,  and  careful 
replacement  and  burnishing  on  the  tooth,  the  collar  and  half  cap  are 
removed,  filled  with  wet  plaster  and  sand,  and  the 
platinum  soldered  to  the  gold.  It  is  then  placed  on 
the  tooth,  burnished  into  all  the  inequalities  of  the 
tooth,  very  carefully  removed,  invested,  and  enough 
solder  flowed  over  the  platinum  to  cover  and  give  it 
strength.  Fig.  891,  B,  shows  it  complete  on  the  cuspid. 
I  have  often  made  such  collars  in  less  than  an 
hour,  and  in  any  case  time  must  be  made  subservi- 
ent to  exactness  of  fit  and  adaptation  to  the  end  in  view."  ^ 

Additional  fixation  may  be  given  these  collars  under  favorable  con- 
ditions through  Dr.  Litch's  expedient  of  the  pin  anchorage.  In  the 
centre  of  the  shoulder  portion  of  each  cap,  before  stiifening  the  cap,  a 
hole  is  drilled,  the  drill  passing  into  the  tooth  for  a  short  distance — 
enough  to  furnish  a  socket  for  a  piece  of  platinum  screw,  but  not  deep 
enough  to  endanger  the  pulp.  A  small  length  of  screw  is  passed  through 
the  opening  into  the  tooth  and  projecting  a  sixteenth  of  an  inch  or  more. 
Adhesive  wax  is  flowed  over  the  end  of  the  screw  and  the  collar  cap  ;  the 
caps  are  withdrawn  and  invested.  A  piece  of  plate,  preferably  of  plat- 
inous  gold  No.  33,  is  annealed,  perforated,  and  bent  and  filed  to  fit  the 
cap,  to  which  it  is  attached  by  means  of  20-carat  solder,  the  solder  flowing 
about  the  exposed  end  of  the  screw,  uniting  it  to  the  plate.  The  pieces 
are  transferred  to  the  teeth.  The  subsequent  operations  are  similar  to 
those  where  the  abutments  are  made  of  post  and  collar  crowns. 

In  the  latter  case  the  teeth  are  decrowned,  as  described  in  Chapter 
XVIII. ;  the  pulp-canals,  and  when  necessary  the  tissues  about  the  apex 
of  the  root,  are  properly  treated,  and  the  ends  of  the  roots  hermetically 
sealed.  The  teeth  or  roots  are  prepared  for  the  reception  of  collar  and 
post  crowns.  It  is  necessary  that  the  walls  of  the  roots  embraced  by  the 
collars  and  the  axes  of  the  pulp-canals  be  so  trimmed  that  they  are  mu- 
tually parallel  :  disregard  of  this  precaution  is  inevitably  followed  by 

'  Mellotte,  Cosmos,  vol.  xxviii.  p.  746. 


THE  MANUFACTURE  OF  DENTAL  BRIDGES.  673 

faulty  adaptation  of  the  crowns,  with  its  attendant  evils.  After  enlarging 
one  pulp-canal,  insert  a  wire,  permitting  it  to  extend  for  more  than  half 
an  inch  from  the  root  face,  to  serve  as  a  guide  line  in  enlarging  the  canal 
of  the  second  abutment. 

When  the  collars  and  posts  have  been  fitted  a  bite  is  taken,  next  a 
plaster  impression  in  which  the  caps  are  withdrawn  or  which  clearly 
and  unmistakably  exhibits  depressions  into  which  posts  and  collars 
may  be  replaced  with  exactitude.  An  exact  shade  is  secured.  A 
model  is  made  and  an  articulation  mounted.  A  set  of  six  plain  plate 
straight-pin  teeth  are  selected,  matching  precisely  the  shade  tooth  taken, 
except  that  the  cuspids  should  have  the  yellow  enamel  extend  farther 
toward  the  edges  of  the  teeth  than  in  the  incisors.  The  teeth  should 
exactly  correspond  in  shape  with  the  natural  teeth,  and  should  be  of  the 
proper  length. 

A  block  of  wax  is  placed  behind  the  teeth  in  which  to  imbed  the  pins. 
They  are  now  carefully  ground,  as  described  in  the  chapter  on  Fitting 
of  Teeth  to  Plates.  There  should  be  sufficient  distance  between  the 
artificial  and  the  antagonizing  teeth  to  permit  the  placing  of  a  rigid 
backing  stay. 

Should  Mellotte's  partial  caps  be  employed,  the  distal  sides  of  the 
laterals  should  be  closely  fitted  to  the  gold,  but  preserving  the  cor- 
rect forms  of  the  teeth.  The  lateral  surfaces  of  the  teeth  should  be  in 
close  contact  for  at  least  the  labial  half  of  their  length.  The  utmost 
care  must  be  exercised  in  this  fitting  that  the  shape  of  each  tooth  shall 
be  correct. 

The  outer  w^all  of  the  impression  is  to  be  varnished,  and  a  plaster 
retaining  wall  built  against  the  labial  faces  of  the  teeth  to  retain  them 
in  position  while  the  stays  are  being  fitted.  Each  tooth  is  to  be  removed 
from  its  bed,  and  bevelled  from  the  cutting  edge  to  just  above  the  upper 
pin,  being  careful  to  preserve  the  correct  outlines  of  the  cutting  edges. 
Stays  covering  the  backs  of  the  teeth  clear  to  the  outer  line  of  the  cutting 
edges  are  fitted,  and  all  of  them  to  be  in  lateral  contact.  These  stays 
are  to  be  made  of  two  layers — tlie  first  of  24-carat  gold,  No.  32,  well 
annealed,  the  second  of  24-carat  gold,  No.  26.  They  are  burnished  into 
accurate  apposition  with  the  backs  of  the 
teeth,  covering  them  completely  and  extend-  Fig.  892. 

ing  to  the  gum  line.  Should  it  be  neces- 
sary to  make  the  stays  thin,  a  layer  of 
platinous  gold,  No.  29,  is  fitted  over  stay 
No.  1,  and  to  be  made  of  the  same  size. 
The  teeth,  with  the  stays  in  position,  are 
withdrawn  from  the  plaster  wall,  and  are 
boiled  in  acid  solution.  The  stays  are  now 
filed  each  to  the  outline  of  the  palatal  aspect 
of  the  tooth.  The  surfaces  of  the  stays  to 
be  united  are  covered  by  borax,  and  the 
pins  split  to  retain  them  in  position.  They 
are  all  placed  in  a  common  investment, 
not  more  than  one-half  inch  thick,  exposing  the  entire  surfaces  of  the 
stays  (Fig.  892),  but  covering  the  porcelain  :  22-carat  solder  is  coated 
with    borax,    a    piece    laid    over   each   pin,    one   at    each  end    of    the 

43 


_  A 


674  AN  ASSEMBLAGE  OF  UNITED   CROWNS, 

stay  and  additional  pieces  over  the  faces  of  the  stays.  The  case  is 
heated  gradually  until  the  borax  fuses  and  holds  the  solder  in  posi- 
tion. A  large  flame  of  the  blowpipe  is  directed  against  the  base  of  the 
investment  until  the  solder  begins  to  fuse,  when  the  investment  is  turned 
over  and  a  smaller  flame  thrown  against  each  stay  until  the  solder  flows 
freely.  The  investment  is  permitted  to  cool  gradually,  and  when  cold 
the  teeth  are  removed  and  boiled  in  acid.  Each  stay  is  now  filed,  giving 
it  a  rounded  form,  the  thickest  part  in  the  middle  and.  curving  to  thin 
edges  laterally ;  at  the  cutting  edge  the  gold  is  to  be  thick  enough  to 
protect  the  porcelain  facings  against  contact  Avith  the 
Fig.  893.  antagonizing  teeth  (Fig.  893).     When  in  position  in  the 

mouth  but  a  faint  line  of  gold  should  be  visible  at  the 
cutting  edges.  Each  stay  is  to  be  smoothed,  and  all  por- 
tions except  those  to  be  soldered  are  buffed  with  pumice. 
They  are  dried  and  returned  to  position  on  the  wall 
upon  the  model ;  the  latter  is  loosened  from  the  model 
and  then  replaced  in  position.  The  teeth  are  reset  in  the  wall  and  their 
joints  united  by  means  of  adhesive  wax.  A  stiff  Avire  is  now  laid  across 
the  backs  of  the  teeth  and  well  covered  with  adhesive  wax,  so  that  all 
four  teeth  are  immovably  held  together.  When  the  wax  is  hard  the 
teeth  are  removed  from  wall  and  model  and  invested.  The  joints 
between  the  centrals  and  between  centrals  and  laterals  are  scraped,  and 
a  piece  of  very  heavy  pure  gold,  preferably  triangular  wire  No.  16,  is 
laid  along  the  joints,  and  two  small  pieces  of  20-carat  solder  on  either 
side  of  each  wire.  The  investment  is  heated  gradually  until  red,  and 
the  teeth  are  joined  together  by  turning  a  fine  flame  against  the  joints. 
The  abutment  crowns  are  removed  from  the  model,  invested,  and  sol- 
dered with  22-carat  solder,  as  described  in  Chapter  XVIII.  When  cold 
the  abutment  crowns  are  placed  in  position  in  the  mouth,  and  the  incisors 
set  in  their  position.  A  piece  of  softened  modelling  compound  pressed 
against  their  palatal  surfaces  will  hold  them  in  their  relative  positions 
when  a  plaster  impression  is  taken,  in  which  the  pieces  are  withdrawn. 
The  impression  is  cut  away  until  it  serves  merely  as  a  means  of  holding 
the  sections  in  position.  A  model  is  made  of  investing  material.  When 
separated  from  the  impression  enough  additional  investment  is  placed 
over  the  porcelain  to  protect  it  from  the  direct  contact  of  the  flame. 
The  joints  between  the  abutment  crowns  and  the  body  of  the  bridge  are 
scraped  clean  and  a  cream  of-  borax  painted  over  them.  Thick  pieces 
of  plate  are  filed  and  bent  to  fit  the  angles  of  junction,  and  sufficient 
20-carat  solder  laid  over  each  joint  to  fill  it  flush. 

The  case  is  heated  slowly,  and  when  the  investment  is  at  a  bright- 
red  heat  the  fine  flame  is  directed  against  each  joint  until  the  solder 
flows  freely.  When  cool  the  piece  is  finished  by  means  of  fine  files, 
emery-cloth,  and  buffs,  then  burnished,  and  finally  polished  with  rouge. 
All  incisor  and  cuspid  facings  are  to  be  made  after  the  manner 
described. 

Some  operators  pour  the  first  model  of  investing  material  and  procede 
with  the  making  of  the  dummies  as  described,  afterward  uniting  the  six 
pieces,  dummies  and  crowns,  in  one  operation.  The  separate  pieces  are 
adjusted  to  the  model ;  sufficient  additional  investment  is  applied  to  hold 
and  protect  the  facings  (Fig.  894).    The  joints  are  scraped  clean,  a  small 


THE  MANUFACTURE  OF  DENTAL  BRIDGES. 


675 


section  of  wire  laid  over  each,  borax  and  solder  are  applied,  and  the  case 
is  soldered  as  described  above. 


Fig.  894. 


Bridges  having  Three  or  More  Abutments. — With  an  increase  of 
area  of  masticating  snrface,  hence  increase  of  the  amount  of  work  to  be 
done  and  stress  to  be  borne,  it  is  advisable,  where  and  when  possible,  to 
prepare  and  utilize  an  additional  abutment,  or  it  may  be  two  of  them. 
With  the  increase  of  the  number  of  abutments  there  is  a  corresponding 
increase  of  difficulty  in  accurately  adapting  the  abutment  crowns.  Again, 
with  an  increase  in  the  jiumber  of  pieces  or  sections  of  the  bridge,  the 
danger  of  distortion  of  the  united  sections  through  contraction  of  the 
solder  or  breakage  of  the  investment  becomes  greater. 

In  trimming  or  shaping  the  abutments  it  is  advisable  to  reduce  each 
to   something  less  than  parallel  sides :   let  them   represent   frusta  of 

Fig.  895. 


pyramids  or  cones.     A  typical  case  of  the  three-abutment  bridge  is  seen 
in  Fig.  895. 

The  abutments  are  prepared  as  described,  the  walls  of  the  abutments 
made  parallel  with  the  axes  of  the  teeth  ;  then  each  is  still  further  re- 
duced to  ensure  that  all  three  collars  may  be  readily  set  in  position  in 
the  finished  piece.  The  pulp-canals  of  the  teeth  to  receive  the  collar 
crowns  are  enlarged  more  than  usual.  Collar  crowns  are  fitted  to  the 
cuspid  and  central  roots,  and  a  barrel  crown  to  the  molar.  An  impression 


676  AN  ASSEMBLAGE  OF   UNITED  CROWNS. 

is  taken  with  plaster,  in  which  all  three  crowns  should  be  withdrawn  if 
the  abutments  have  been  properly  trimmed.  A  cast  of  investing  material 
is  made,  a  wax-bite  which  has  been  taken  is  adjusted,  and  an  articulation 
made,  A  lateral  incisor  is  fitted  as  before  described  ;  dummies  of  the 
usual  type  are  made  and  united  in  one  block.  The  lateral  and  the  dummy 
blocks  are  fitted  in  position  and  held  by  means  of  wax.  Wax  flux  is 
melted  in  the  joint  between  the  masticating  surfaces  of  the  dummy  blocks 
and  the  crowns,  so  that  the  retaining  investment  will  not  enter  these 
spaces.  An  undercut  is  made  in  the  model  above  the  neck  lines  of  the 
teeth  ;  it  is  immersed  in  water,  and  sufficient  investing  material  is  built 
over  the  porcelain  and  gold  to  hold  the  pieces  in  position.  When  it  is 
hard  the  model  portion  of  the  investment  is  cut  away,  so  that  a  fine  flame 
will  enter  readily  beneath  the  gold  portion  of  the  dummies.  The  lines 
of  junction  are  cleansed  and  painted  with  borax,  pieces  of  plate  laid 
over  them,  together  with  sufficient  solder  (20-carat)  to  fill  the  joints 
completely. 

The  investment  must  be  dried  and  warmed  thoroughly  before  heating 
for  soldering  to  ensure  that  the  two  sections  of  investment  do  not  separate. 
The  case  is  heated  from  the  investment  side  to  a  red  heat,  the  hottest 
portions  to  be  immediately  over  the  joints  to  be  soldered.  Solder  as 
usual  with  a  fine  flame. 

The  principle  of  construction  is  the  same  when  a  bicuspid  is  the  mid- 
dle abutment ;  however,  in  that  event  the  crown  is  to  be  of  the  barrel 
variety,  with  or  without  a  porcelain  face.     (See  Fig.  896.) 

In  the  soldering  of  these  and  all  other  bridges  it  is  desirable  to  have 
as  few  joints  as  possible  to  be  united  in  the  final  soldering.    For  instance, 
in  such  a  case  as  Fig.  895  it  is  prudent  to  construct 
Fig.  896.  first  the  separate  crowns  and  dummies ;  next  unite 

the  two  crowns,  the  central  and  cuspid,  with  the 
lateral  incisor;  next  unite  the  other  dummies  to- 
gether ;  and  finally,  unite  the  pieces  as  they  now  are 
on  a  cast  of  investing  material  poured  in  a  plaster 
impression,  in  which  the  small  primary  bridge  and 
the  molar  crown  have  been  withdrawn. 
Cases  having  Four  Abutments. — With  four  abutments  about  the 
utmost  limit  of  available  resistance  is  utilized,  even  with  the  most  exten- 
sive bridge-work.  The  typical  example  of  this  variety  of  bridge  base  is 
seen  in  Fig.  897.  The  bridge  and  its  abutments  are  guarded  at  four 
angles,  the  points  of  greatest  resistance  against  displacement.  In  the 
illustration  one  abutment  is  seen  to  be  prepared  for  the  reception  of  a 
bar  anchorage.  This  type  of  fixation,  while  lessening  practically,  though 
not  theoretically,  the  amount  of  resistance  affiDrded,  renders  accurate 
placement  more  easy  than  when  a  firmer  abutment  (a  barrel  crown)  is 
employed. 

The  first  stage  of  the  operation  after  trimming  the  abutments,  as 
before  described,  is  the  making  of  the  molar  crown  and  of  the  collars 
and  posts  of  the  cuspid  crowns.  In  order  to  fit  the  porcelain  teeth 
properly  and  artistically  a  wax-bite  and  an  impression  of  the  lower 
teeth  are  taken  ;  next  a  plaster  impression  in  which  the  crown  bases  are 
withdrawn.  Casts  are  made  in  the  plaster  and  wax  impressions  and  an 
articulating   model   mounted   (Fig.   898).     The   articulator   should   be 


THE  MANUFACTURE  OF  DENTAL  BRIDGES. 


677 


preferably  that  of  Bonwill,  to  ensure  the  maximum  of  utility  in  the 
finished  piece.     The  antagonizing  teeth  are  varnished  with  shellac. 


Fig.  897. 


It  is  advisable  to  defer  the  full  cutting  of  the  groove  or  shaping  it 
in  the  molar  until  it  has  been  determined,  by  arranging  the  teeth,  what 
should  be  its  outlines.  A  set  of  the  six  anterior  teeth  are  selected,  and 
bicuspid  and  molar  facings  which  correspond  in  shape,  size,  and  shade 
with  the  natural  teeth.  The  anterior  teeth,  including  the  facings  for 
the  cuspids,  are  fitted,  adjusted,  stayed,  and  soldered  as  for  the  bulk- 
head bridge.  The  bicuspid  and  molar  dummies  are  made 
as  for  the   first  bridge  described. 

When  the  facing  next  to  the  slotted  abutment  has  been 
adjusted  and  the  stay  fitted,  the  line  of  its  wall  is  marked 
on  the  plaster  tooth,  which  is  carved  out  to  the  form  repre- 
sented in  Fig.  897,  and  an  iridio-platinum  bar  is  fitted  rest- 
ing against  the  stay,  as  in  Fig.  899,  to  which  it  is  attached 
by  means  of  adhesive  wax  and  invested,  the  investment  covering  that 
portion  of  the  bar  which  is  to  extend  into  the  cavity. 


Fig.  899. 


678 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


In  the  event  of  there  being  rigid  restriction  in  regard  to  the  amount 
or  direction  of  cutting  the  slot  in  the  natural  tooth,  this  may  be  done 
first  and  the  bar  and  dummy  be  made  to  conform.  The  dummies  may 
be  now  joined  in  three  sections — first,  the  incisors ;  second,  the  lateral 
blocks,  right  and  left.  The  cuspid  crowns  are  soldered  as  a  separate 
operation.  The  abutment  crowns  are  then  placed  in  position  in  the 
mouth  :  it  may  be  that  it  will  be  necessary  to  enlarge  or  alter  the  shape 
of  the  slot  in  the-  molar  abutment. 

Some  operators  form  the  model  of  investing  material  so  that  it 
may  serve  as  a  soldering  base.  It  is  a  safer  plan  to  be  certain  of  the 
absolute  accuracy  of  each  step  of  the  operation,  even  though  this  neces- 
sitates the  taking  of  .several  impressions. 

Adhesive  wax  is  applied  to  the  sides  of  the  dummy  blocks  which 
adjoin  the  abutment  crowns ;  while  this  is  still  soft  the  latter  crowns  are 
dried  and  the  blocks  set  in  position,  and  the  patient  directed  to  bite  on 
them.  As  soon  as  this  wax  is  hard  a  plaster  impression  is  taken  in 
which  the  several  pieces  are  withdrawn  (Fig.  885).  Should  they  not  be 
withdrawn  in  the  impression,  it  is  evident  that  they  will  not  when 
united  go  into  place  with  sufficient  readiness,  so  it  is  more  prudent  to 
reduce  the  walls  of  the  abutment,  which  lock  its  crown,  to  a  greater 
slope,  then  readjust  the  sections  in  the  mouth,  cementing  them  together, 
and  again  essay  the  impression-taking.  The  portions  of  the  impression 
overlying  the  porcelain  facings  are  cut  away,  and  a  model  of  investing 

Fig.  900. 


material  made ;  the  case  is  soldered  as  in  the  former  type,  using  greater 
care  and  deliberation  in  the  heating.  During  the  finishing  of  these 
extensive  pieces  it  is  a  wise  precaution  to  fill  the  concavities  of  the 
crowns  with  plaster. 

The  following  case  will  illustrate  the  imperative  indication  for  bridge- 


BRIDGES  WITH  BREAKS  IN  THE  CONTINUITY  OF  THEIR  BODY.   679 

work,  and  serve  as  an  example  of  the  first  rule  given  for  its  practice : 
"  Is  a  bridge  demanded  by  the  conditions  presenting?"  and  not,  "Is  it  pos- 
sible to  apply  a  bridge  denture  ?  "  The  cuspid  crowns  are  in  situ — that 
upon  the  right  side  pulpless,  that  upon  the  left  carious ;  the  left  superior 
third  molar  containing  a  large  amalgam  filling,  the  first  superior  molar 
of  the  right  side  pulpless,  the  seat  of  an  obstinate  apical  abscess.  The 
patient  had  worn  a  disfiguring  plate  denture,  which  performed  no  ser- 
vice, physiological  or  eesthetic.  At  the  apex  of  the  vault  and  extending 
to  the  soft  palate  was  a  large  bony  protuberance  :  this  furnishes  objec- 
tion No.  1  against  a  vacuum  plate.  There  was  but  little  alveolar  ab- 
sorption ;  the  gum  at  the  sites  of  the  lost  teeth  had  a  normal  contour. 
The  inferior  incisors  had  elongated  and  protruded  beyond  their  normal 
arch,  making  the  adaptation  of  appropriate  artificial  teeth  an  impossi- 
bility. Upon  mounting  articulating  models  it  was  found  that  as  the 
jaws  of  the  articulator  were  separated  the  tips  of  the  inferior  incisors 
receded  until,  when  the  molars  were  separated  something  less  than  one- 
eighth  of  an  inch,  it  was  possible  to  adjust  anatomically  correct  artificial 
incisors.  The  indication  being  that  this  alteration  of  occlusion  or  per- 
manent separation  of  the  jaws  be  made  in  order  to  adjust  the  artificial 
denture,  it  is  obvious  that  the  bite  must  be  altered  to  the  extent  exhib- 
ited, and  that  the  cuspids  be  extended  until  the  bite  rests  at  its  four 
angles.     Bridge-work  should  therefore  be  a  demand,  not  a  choice. 

The  abscess  upon  the  molar  to  be  obliterated  ;  the  pulpless  cuspid  de- 
crowned ;  the  carious  cuspid  prepared  and  filled,  and,  as  its  form  was 
almost  cylindrical,  have  its  lateral  walls  made  parallel.  The  filled 
molar  was  trimmed  so  that  its  walls  were  parallel  with  the  other 
abutments. 

Crowns  were  fitted  to  the  molars,  raising  the  bite  one-eighth  of  an 
inch,  the  amount  necessary  ;  a  collar  and  post  crown  to  one  cuspid  upon 
the  other  cuspid,  an  open  cylinder,  cut  away  at  its  anterior  aspect  to  one- 
eighth  of  an  inch  in  width  and  covering  completely  the  remainder  of 
the  crown.  Shoulders  were  attached  to  the  cuspid  pieces  in  such  position 
that  all  the  abutments  were  in  occlusion  and  the  bite  raised  the  necessary 
extent.  A  wax-bite,  an  impression  of  the  lower  teeth,  and  a  plaster  im- 
pression in  which  the  abutments  were  withdrawn  were  taken.  Models 
were  mounted  in  the  Bonwill  articulator,  and  appropriate  teeth  and 
dummies  were  formed  and  fitted.  They  were  united  in  blocks,  the 
crowns  and  blocks  adjusted  in  position  in  the  mouth,  a  plaster  impression 
taken,  a  base  made  of  investing  material,  and  the  sections  were  united. 
There  was  some  slight  inconvenience  following  the  placement  of  the 
bridge,  due  to  the  lengthened  bite,  which  soon  disappeared  ;  the  piece  has 
been  worn  several  years  with  much  comfort. 

Bridges  with  Breaks  in  the  Continuity  of  their  Body. 

Cases  present  which  may  exhibit  conditions  favorable  for  the  employ- 
ment of  bridge-work,  except  that  at  some  part  of  the  arch  there  is  a 
tooth  which  may  be  mechanically  unnecessary  in  the  support  of  a  bridge, 
and  which  it  is  the  part  of  wisdom  to  leave  out  of  the  bridge  structure. 
It  may  be  that  the  tooth  has  such  a  lack  of  parallelism  between  its  axes 
and  those  of  the  abutments  that  its  utilization  is  impracticable.     The 


680 


AN  ASSEMBLAGE  OF  UNITED  CROWNS. 


author  of  the  only  satisfactory  device  for  application  in  such  cases  is  Dr. 
J.  L.  Williams.^ 

Fig.  901.  Fig.  902. 


The  connecting  bars    may  be  formed    by  annealing  and   flattening 

'  Cosmos,  1885,  Dec. 


EXTENSION  BRIDGES. 


681 


slightly  bars  of  iridio-platinum  wire  No.  14 ;  these  are  bent  about  the 
necks  of  the  teeth,  not  quite  touching  them,  their  ends  resting  solidly 
against  the  stays  of  the  dummies.  A  typical  case  is  illustrated  in  Figs. 
901,  902,  903.  A  modified  form  of  the  same  device  is  seen  in  Fig.  904. 
The  device  proves  useful  in  such  cases  as  the  following  :  A  crownless 
lateral  with  a  good  root ;  an  unblemished  cuspid  ;  the  first  bicuspid  absent 
and  the  second  bicuspid  root  fit  to  serve  as  an  abutment.  A  bridge  is 
constructed,  the  lateral  and  second  bicuspid  having  abutment  crowns 
adapted ;  a  dummy  replaces  the  first  bicuspid,  and  the  connecting  bar 
passes  around  the  palatal  portion  of  the  cuspid,  resting  lightly  upon  the 
gum. 

Extension  Bridges. 

The  principle  of  construction  of  this  variety  of  bridge-work  is  that  of 
a  portion  of  the  body  of  a  bridge  extending  beyond  an  abutment,  and 
having  attachment  at  but  a  single  point.  It  will  be  seen  that  there  is 
involved  a  faulty  and,  it  may  be,  vicious  mechanical  principle.  It  is  a 
variety  of  structure  which  has  no  counterpart  in  bridges  as  the  engineer 
knows  them. 

The  danger  attending  or  following  its  employment  is  mechanical  dis- 
placement of  the  abutment  itself,  the  danger  being  in  the  direct  ratio  of 


Fig.  905. 


Fift.  906. 


the  amount  of  force  received  by  and  through  the  extension,  and  in  the 
inverse  ratio  of  the  number  and  strength  of  the  abutments. 


A  consensus  of  contemporary  opinion  places  these  devices  in  the  cate- 
gory of  abuses  of  bridge-work. 


682 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


The  mildest  form  of  the  above  is  seen  in  such  a  fixture  as  Fig.  906. 

Faulty  though  the  design  may  be,  it  cannot  be  denied  that  there  are 
cases  in  which  the  employment  of  the  work  is  justifiable. 

The  force  received  upon  such  a  fixture  as  Fig.  906  necessarily  tends 
to  rotate  the  abutment  crown  or  even  the  root  itself;  the  same  objection 
obtains  with  any  fixture  supported  by  but  one  abutment.  The  details 
of  construction  of  such  a  piece  and  of  Fig.  905  are  evident. 

Figs.  907,  908,  and  909  (after  Dr.  Parr)  exhibit  a  case  in  which  the 
extensive  work  figured  has  its  justification  in  the  advantages  afforded  by 


Fig.  908. 


Fig.  909. 


^'4i i^luJii' 


such  a  piece  over  a  plate  denture,  so  long  as  the  abutments  maintain 
their  fixation.  It  is  to  be  recognized  that  this,  as  in  other  extreme  cases 
of  bridge-work,  is  governed  by  matters  of  economy. 

It  is  necessarily  doubtful  how  long  the  abutments  will  persist  in  a 
condition  of  secure  fixation,  so  that  the  question  concerns  the  purse  of 
the  wearer :  Can  he  aflPord  (financially)  to  pay  the  fee  for  such  an  appli- 
ance for  the  term  of  service  it  is  likely  to  afford  him  ? 

The  proper  construction  and  adaptation  of  such  pieces  tax  to  the 
utmost  the  skill,  knowledge,  and  ingenuity  of  the  expert  mechanic ;  the 
novice  is  wise  in  avoiding  them. 

The  figures  illustrate  the  most  extensive  apparatus  anchored  to  abut- 
ments which  dental  literature  records.  The  crowns  and  dummies  of 
such  cases  are  constructed  after  the  methods  described.  Oval  plates  of 
gold  are  swaged  to  cover  a  greater  area  of  the  ridge  than  embraced  by 
the  base  of  the  teeth  they  are  to  support.  Upon  them  plate  teeth  or  all- 
gold  crowns  may  be  fitted,  and  attached  to  the  terminal  dummies. 


Removable  Bridges. 

These  are  devices  which  are  so  attached  to  abutments  that  they  may 
be  removed  by  the  operator  for  the  purpose  of  repair  or  to  gain  access  to 
abutments  which  might  possibly  require  therapeutic  aid ;  again,  as  a 
means  of  bridging  spaces  to  which,  owing  to  the  position  of  the  abut- 
ments, it  would  be  impracticable  to  properly  adapt  fixed  bridges.  Others 
are  designed  and  attached  so  that  the  patient  may  remove  them  for 
hygienic  considerations. 

The  first  consideration  is  the  perfect  protection  of  the  abutments 
themselves  against  the  entrance  of  fermentable  material,  otherwise  the 
spaces  existing  between  the  abutment,  crowns,  and  these  bases  them- 


REMOVABLE  BRIDGES. 


683 


selves  would,  by  filling  with  the  causes  of  dental  caries,  bring  about  the 
dissolution  of  the  abutments. 


Fig.  910. 


In  devising  this  variety  of  bridge  or  in  applying  devices  it  is  prefer- 
able to  select  those  whose  mode  of  retention  and  method  of  construction 


Fig.  911. 


are  simple.     For  example,  Fig.  916  would  be  preferable  to  Fig.  920, 
being  more  readily  constructed. 


684 


AN  ASSEMBLAGE   OF   UNITED   CROWNS. 


The  means  of  anchorage  of  this  variety  of  bridge-work  is  either 
through  telescoping  barrels ;  posts  fitting  in  sockets  anchored  in  the 
roots  of  teeth  ;  attachment  by  means  of  screw  sockets  in  prepared  abut- 
ments ;  by  variously  shaped  sockets  in  the  body  of  the  bridge  or  attached 
to  the  abutment  crowns,  in  which  closely-fitting  posts  are  slipped.  Their 
degrees  of  simplicity  are  in  the  order  named. 

The  first  of  these  devices  was  that  of  Dr.  R.  W.  Starr  ^  (Fig.  910). 
The  abutment  teeth  were  trimmed  to  a  form  which  permitted  the  adjust- 
ment of  ferrules  which  were  cemented  to  their  bases. 

Telescoping  barrels,  with  properly  occluding  caps,  are  fitted  over 
these,  being  cut  away  at  such  aspects  as  would  prevent  their  placement 
in  a  common  piece.  A  dummy  crown  is  fitted  between  and  attached  to 
them.     The  pieces  were  set  with  gutta-percha. 

The  same  principle  is  applied  in  Figs.  912-916.^ 

The  illustrations  explain  in  themselves  the  methods  and  steps  of  the 
construction. 


Fig.  912. 


Fig.  913. 


Another  method  of  applying  a  removable  bridge  to  similar  cases  is 
that  of  Dr.  R.  B.  Winder.  Collars  are  fitted  to  the  abutments,  to  which 
perfectly  flat  caps  are  soldered.  A  bite  and  impression  are  taken  in 
which  the  caps  are  withdrawn.  Occluding  caps  are  formed,  which  are 
filled  flush  with  solder  and  ground  flat  to  fit  the  ferrule  tops.  Dummies 
are  constructed  and  united  to  one  another.  The  caps  are  to  be  attached 
either  by  screws  passing  into  the  crowns  of  the  abutments  or  else  by 
nuts  passing  over  screws  which  have  been  attached  to  the  ferrule  tops, 
over  which  the  occluding  cap  is  set,  being  perforated  for  the  passage  of 
the  screws.  It  is  advised  that  the  pieces  be  now  placed  in  position  in 
1  Cosmos,  1886.  2  y.  M.  Willis,  D.  D.  S. 


REMOVABLE  BRIDGES. 


685 


the  mouth,  held  together  by  means  of  adhesive  wax.  Over  the  pieces 
investing  material  is  placed  sufficient  to  hold  them  together ;  they 
are  then  encased  in  investment  and  the  caps  attached  to  the  dummy 
block. 

Holes  may  be  drilled  through  the  deepest  part  of  the  cap  large 
enough  to  admit  the  screws,  and  continued  into  the  crowns  as  deep  as 
the  screws  are  long.  The  holes  in  the  crowns  may  be  enlarged  and  the 
screws  slightly  oiled.  Zinc  phosphate  is  placed  in  the  pits,  the  bridge 
is  set  in  position,  and  the  screws  thrust  into  the  cement  while  the  latter 
is  still  soft. 

These  forms  of  bridges  are  applicable  where  the  abutment  teeth 
incline  toward  one  another  at  such  an  angle  as  to  render  the  placing 
of  complete  cylinders  impracticable  or  impossible.  The  more  general 
employment  of  the  same  or  similar  methods  in  many  of  the  cases  which 
receive  fixed  bridges  would  remove  many  of  the  objections  urged  against 
the  latter. 

Fig.  917. 


An  applicable  and  w^ell-devised  appliance  is  shown  in  Fig.  917,^  in 
which  fixation  of  the  bridge  to  the  abutments  is  secured  by  means  of  a 

^  Dr.  C.  L.  Alexander. 


686 


^JV  ASSEMBLAGE  OF   UNITED  CROWNS. 


Fig.  919. 


telescoping  collar  placed  over  a  capped  root,  its  other  extremity  having 
a  socket  fitted  to  and  slipped  over  a  retaining  shoulder. 

A  bridge  held  by  two  similar  shoulders,  but  removable  outwardly, 
is  shown  in  Fig.  918  :  it  is  designed  to  overcome  the  tendency  to  dis- 
placement by  the  stress  of  mastication  present  in  those  devices  which  are 
inserted  vertically. 

Dr.  Parr's  method  of  constructing  these  telescoping  ends  is  by  far 
the  simplest  offered.     Two  pieces  of  platinum  plate  are  shaped  as  in 

Fig.  919,  so  that  one  shall  telescope  the 

other :  the  inner  one  is  filled  flush  with 

wax  and  invested ;  the  wax  is  removed, 

the  space  is  filled  by  melting  gold  plate 

in  it.      The  outer  section  is  filled   with 

'^^^        f^^^'^A^  investment,  and  its  walls  are  made  rigid 

>l\    l£i^^rT.l  by  flowing  gold  over  them,   or,  what  is 

'     *^i    ^^-^^^  preferable,  adding  thick  pieces  of  plate  to 

each  side  and  joining  them  by  means  of 
22-carat  solder.  The  shoulders  are  soldered  to  the  crowns,  the  slots  are 
adjusted  to  the  shoulders,  their  ends  attached  to  the  stays  of  the  dum- 
mies. It  is  necessary  that  the  slots  should  be  immovably  held  against 
the  stays  to  ensure  their  correct  position  in  the  finished  piece.  Soft 
adhesive  wax  is  placed  around  them,  attaching  them  to  the  backings, 
an  unusually  large  amount  of  the  wax  being  used.  The  piece  is  chilled 
and  the  dummies  and  sockets  withdrawn.  If  both  sockets  come  away 
without  detachment,  the  piece  is  immediately  invested ;  if  one  or  both 
have  broken  away,  the  sharp  line  of  fracture  of  the  brittle  cement  fur- 
nishes the  guide  for  their  accurate  replacement. 

The  writer  advises  that  the  free  ends  of  the  shoulder-piece  be  left  as 
extensions  which  are  adapted  to  the  wall  of  the  abutment  crown,  the 
socket  piece  to  have  similar  wings  which  shall  outline  the  terminal  wall 
of  the  bridge  body  in  its  finished  state. 

In  the  Curtis  bridge^  (Figs.  920  and  921)  the  long  arms  (1,  Fig.  921) 
are  made  of  heavy  platinous  gold  plate,  the  heads  formed  in  the  matrix  E 


Fig.  921. 


2        1 


(Fig.  922).     Sockets  (2)  of  thin  gold  are  made  fitting  these  arms  closely. 

The  dummy  crowns  have  had  their  caps  fixed  by  solder  to  hold  them  in 

position.     The  sockets,  with  their  ends  projecting  beyond  the  borders 

^  G.  L.  Curtis,  Cosmos,  vol.  xxxii.  p.  109  et  seq. 


REMOVABLE  BRIDGES. 


687 


of  the  dummies,  are  attached  to  the  latter  by  means  of  fluxed  wax.  The 
pieces  are  invested,  and  the  sockets  are  attached  by  means  of  solder, 
completing  in  this  soldering  the  contour  of  the  dummy  block  (C,  Fig. 


Fig.  922. 


920).  The  surfaces  of  the  dummies  are  cut  away  until  the  block 
fits  closely  between  the  crowns.  The  block  is  now  smoothed  and 
buffed.  The  arms  are  placed  in  their  sockets,  from  which  they  project 
at  their  under  surfaces.  The  palatal  surface  of  the  cast  is  varnished  ; 
the  dummy  block  containing  the  arms  is  set  in  position  :  attach  the 
block  to  the  cast  by  a  drop  of  adhesive  wax  melted  at  the  junction  of 
the  porcelain  with  the  cast.  In  the  depression  beneath  the  dummies 
pour  soft  investing  material.  When  this  has  set  remove  the  bridge, 
and  a  depression  is  seen  in  the  investing  material,  in  which  the  bar 
which  made  it  is  placed.  Enough  investment  is  added  to  hold  the  bars 
in  position,  which  are  to  be  perfectly  united  to  the  abutment  crowns  by 
means  of  solder. 

These  bridges  are  attached  by  cementing  both  crowns  to  their  abut- 
ments with  one  mix  of  cement,  and  while  this  is  still  soft  quickly  set- 
ting the  body  of  the  bridge  in  position. 

A  variety  of  removable  bridge,  the  design  of  which  suggests  it  as 
one  of  wide  application,  is  that  of  Dr.  C.  M.  Richmond.^     A  model 
and  zinc  die  are  made  of  the  abutment  molar  with  its  crown.     Around 
this  crown  a  telescoping  collar  is  made, 
fitting    it    tightly :    this    is    made    of 
crown    metal,  about    one-sixteenth    of 
an  inch  longer  than  the  crown.     The 
die  is  driven  into  this  collar,  and  the 
surplus  length  is  swaged  to  overlap  the 
occlusal    surface    of    the     crown.      A 
second   collar   is   adapted  to   the   first 
and  the  two  united  with  solder,  form- 
ing  a   removable,    rigid,    and   closely- 
adapted  abutment  piece.    The  other  ex- 
tremity of  the  bridge,  its  second  abutment  piece,  is  a  removable  post  crown. 

Dr.  M.  L.  Rhein  ^  has  devised,  applied,  and  furnished  the  models  for 


Fig  923 


Cosmos,  vol.  xxviii.,  No.  8,  p.  497. 


■^  Cosmos,  vol.  xxxvi.  p.  97. 


688 


AN  ASSEMBLAGE  OF  UNITED   CROWNS. 


one  of  the  most  ingenious  forms  of  removable  bridge  yet  presented.  It 
is  designed  to  overcome  the  several  disadvantages  incidental  to  the  pla- 
cing of  a  fixed  bridge,  to  obviate  the  necessity  for  the  occasionally  great 
mutilation  of  abutment  teeth,  to  enable  the  operator  to  apply  a  correctly 
fitting  barrel,  and  to  reproduce  the  slight  movement  possessed  by  the 
natural  teeth  in  normal  occlusion. 

Fig.  924. 


The  distinguishing  feature  of  the  bridge  (Fig.  924,  3)  is  the  abut- 
ment crown  made  in  such  a  manner  as  to  fit   closely  the  neck  of  a 


Fig.  925. 


crown,  smaller  at  this  part  than  at  its  occlusal  edge,  without  mutilating 
the  walls  of  the  crown.     In  constructing  the  crown  an  accurate  plaster 


REMOVABLE  BRIDGES. 


689 


impression  of  it  is  to  be  secured  and  a  perfect  model  made  in  it.  [The 
writer  suggests  the  advisability  of  making  this  cast  of  one  of  the  fusible 
alloys  poured  in  the  plaster  impression.]  The  cast  is  trimmed  away  so 
that  the  band  may  go  one-thirty-second  of  an  inch  beyond  the  gum 
line.  The  natural  crown  is  shortened  sufficiently  to  allow  for  the  proper 
thickness  of  an  articulating  face  on  the  crown  after  the  impression  has 
been  taken.  A  piece  of  plate,  20-carat,  29  gauge,  is  swaged  to  cover 
the  occlusal  face  and  the  walls  of  the  crown  to  the  swell  of  the  tooth 
{B,  Fig.  927). 

A  pattern  is  made  of  heavy  foil.  This  may  be  done  readily  by 
bending  a  piece  of  tin  to  fit  approximately  the  joint  at  the  middle  of  the 
anterior  face  of  the  abutment  crown  :  the  ends  of  the  pattern,  left  long, 
are  grasped  between  the  jaws  of  a  pair  of  pliers  and  drawn  tight  against 
the  walls  of  the  crown  :  the  edge  of  the  tin  is  cut  out  to  follow  the  gum 
outline  closely,  and  again  drawn  tight  by  means  of  the  pliers ;  the  ends 
are  left  extending  some  three-sixteenths  of  an  inch  (C,  Fig.  927).     The 


Fig.  927. 


Ftg.  928. 


pattern  is  reproduced  in  22-carat  plate,  gauge  30.  A  piece  of  pure  gold 
is  sweated  to  the  free  edge  of  the  band,  which  is  then  closely  adapted 
to  the  model  tooth.  A  piece  of  mica  is  placed  in  the  joint  of  the  pro- 
jecting tips,  to  prevent  their  union  in  soldering  on  the  cap,  which  is 
adjusted  in  position  and  soldered  to  the  band. 

The  shortest  distance  between  the  abutment  crowns  is  marked  on  a 
piece  of  card-board,  which  is  then  squared  to  that  width.  Its  edge,^  ap- 
plied to  the  gum  (Fig.  928),  is  cut  to  conform  to  the  gum  outline  in  a 
line  which  marks  beneath  the  narrowest  distance  between  the  abutments. 
The  second  abutment  crown  is  constructed  and  both  are  set  in  position 
on  the  model.  The  card-board  is  placed  in  position,  resting  upon  the 
projecting  ends  of  the  collar  ends,  and  the  lines  of  its  edges  marked  on 
these  by  means  of  a  sharp  blade.  Pieces  of  perfectly  triangular  wire, 
half  the  width  of  the  gib  and  longer  than  the  crown  itself,  are  cut,  two 


44 


690 


AN  ASSEMBLAGE   OF   UNITED   CEOWNS. 


for    each  crown.     One  of  these    has  an  edge  placed    along  the  knife- 
mark  and  cemented  into  position  by  means  of  wax  flux  (Fig.  927,  E). 


A  piece  is  placed  on  the  second  arm,  exactly  opposite  and  parallel  with 
the  first,  and  it  is  similarly  attached.     A  thin  shaving  of  mica  is  placed 


Fig, 


.  between  the  projecting  arms  of  the  crown  ;  the  piece  is  invested,  and  the 
wires  attached  by  the  minimum  of  solder.  The  crowns  are  boiled  in 
acid ;  the  projecting  ends  of  the  wires  are  cut  off,  and  the  upper  ends 
given  a  rounded  bevel.  The  projecting  ends  of  the  crown  arms  are 
filed  flush  with  the  edges  of  the  wires  (Fig.  927,  F).  [The  wires  them- 
selves are  filed  flat  to  present  a  common  surface  anteriorly.] 

The  key  (Fig.  927,  6r)  is  formed  of  platinous  gold  in  the  following 


COMBINATIONS  OF  PLATE- AND  BRIDGE-WORK.  691 

manner  :  A  piece  of  steel  wire  (triangular)  is  slightly  flattened  upon  one 
side  {A,  Fig.  929).  A  small  rectangle  of  platinous  gold,  29  gauge, 
its  short  side  wider  than  the  length  of  the  gib,  is  cut  (Fig.  929,  B), 
and  on  its  surface  the  greatest  width  of  the  gib  is  marked.     The  plate  is 


bent  over  at  one  of  these  lines,  placed  in  a  vise,  the  short  arm  of  plate 
against  the  wire,  F ;  an  arm  is  made,  C.  Turn  the  metal  in  the  vise, 
and  form  the  other  side,  D,  the  base  of  the  piece  measuring  the  extreme 
width  of  the  gib.  Saw-cuts,  made  at  the  angles  to  the  depth  of  the 
bevel  of  the  gib,  will  permit  bending  arms  together  and  forming  a  cap 
to  the  key  {G,  Fig.  927)  :  the  joints  are  soldered  and  the  key  cut  away 
until  it  is  the  length  of  the  gib.  The  gib  and  key  are  accurately  fitted 
to  one  another.  The  pieces  adjusted  in  position,  the  crown  is  represented 
in  J  (Fig.  927).  A  second  piece,  similar  to  the  key,  is  fitted  over  the 
latter  to  serve  as  the  slot  of  the  bridge. 

The  body  of  the  bridge  is  formed  with  the  slots  attached,  as  described 
■on  p.  686.  The  abutment  crowns  are  set  by  removing  the  keys,  placing 
in  the  crowns  sufficient  zinc  phosphate,  and  carrying  them  into  position, 
when  the  keys  are  adjusted  and  forced  fully  into  position,  drawing  the  edges 
of  the  crowns  into  close  apposition  with  the  necks  of  the  teeth.  The  pure 
gold  edges  are  now  burnished  into  perfect  contact  with  the  teeth.  A 
bridge  made  and  attached  after  this  method  is  shown  in  Fig.  930. 

Combinations  of  the  Principles  op  Plate-  with  those  of 

Bridge-work. 

The  principle  involved  in  this  class  of  mechanism  ^vas  utilized  early 
in  the  present  century  as  a  means  of  retention  for  partial  dentures. 
There  is  a  combination  of  the  support  represented  in  the  bearing  of  a 
plate  upon  the  alveolar  ridge,  together  with  the  rigidity  secured  by 
having  terminals  or  extensions  from  the  plate  anchored  in  the  roots  of 
teeth  or  embracing  them  as  closed  and  rigid  cylinders. 

The  principle  of  anchorage  in  the  roots  of  a  natural  tooth  is  illus- 
trated in  Figs.  932  and  933 ;  that  of  embracing  the  natural  teeth  by 


692 


AN  ASSEMBLAGE  OF   UNITED  CROWNS. 


closed  cylinders,  in  Fig.  934 ;  a  combination  of  the  two  means  of  reten- 
tion, in  Fig.  935. 

These  devices  possess  certain  advantages  over  clasp  plates,  in  that 
there  is  no  elasticity  of  the  retaining  cylinders  :  they  slip  over  the  abut- 


FiG.  932. 


Fig.  933. 


ments  prepared  for  their  reception,  and,  being  closely  adapted  to  them, 
there  is  a  greater  rigidity  of  the  dentures  than  with  the  ordinary  clasp. 

For  their  employment  it  is  obviously  necessary  that  the  abutments 
should  have  sides  which  are  parallel  and  the  axes  of  both  mutually 


Fig.  934. 


Fig.  935. 


parallel.  They  are  usually  designed  for  application  in  cases  where  the 
natural  teeth  are  in  such  positions  and  have  forms  which  would  fit  them 
to  serve  as  bridge  abutments,  but  the  contour  of  the  gum  is  such  that  it 
is  necessary  to  employ  gum  teeth  (Fig.  936).  They  are,  to  all  intents  and 
purposes,  removable  bridges,  having  a  greatly  multiplied  support  from 
the  natural  gum. 

It  was  stated  (p.  671),  in  describing  the  bulkhead  bridge,  that  should 
the  contour  of  the  gum  be  lost  to  such  an  extent  as  to  preclude  the  ap- 
plication of  a  bridge,  owing  to  the  impossibility  of  correctly  adapting 
plain  teeth,  a  removable  plate  bridge  might  be  employed.  A  removable 
bridge  may  be  adapted  to  such  a, case  as  follows  : 

The  cuspid  roots  are  properly  trimmed  and  capped.  Removable 
crowns  are  fitted  to  them.  A  gold  plate  is  swaged  to  fit  the  gum  be- 
tween the  teeth,  extending  high  enough  on  its  labial  aspect  to  furnish 
adequate  support  to  the  artificial  gums,  and  the  palatal  edges  far  enough 
to  furnish  adequate  support  to  the  stays  of  the  teeth.  The  plate  is  to  be 
made  of  two  layers — that  next  the  natural  gum  of  No.  32  pure  gold,  and 
covered  by  a  plate  of  No.  32  platinous  gold :  the  two  are  accurately 
adapted  to  one  another  and  united  by  means  of  20-carat  solder.  The 
ends  are  to  be  accurately  adapted  to  the  abutment  crowns.  Plate  and 
crowns  are  set  in  position  in  the  mouth,  and  a  wax-bite  taken  :  this  is 
removed  and  set  aside.  While  the  pieces  are  in  position  an  impression 
of  modelling  compound  is  taken.  Modelling  compound  is  preferred  to 
plaster,  because  the  pressure  upon  the  plate  forces  the  latter  into  accurate 
contact  with  the  soft  tissues.  Should  plaster  be  employed,  a  ridge  of 
softened  wax,  wide  enough  to  fit  between  the  abutments,  is  set  in  the 
impression  tray,  and  over  it  the  plaster.     Now,  when  the  impression  is 


PORCELAIN  BRIDGE-WORK. 


693 


taken  the  plate  is  pressed  up  by  the  wax  sufficiently  to  ensure  that  the 
natural  gum  shall  furnish  support  to  the  finished  bridge.  A  model  is 
made  and  an  articulation  mounted.  Should  the  plate  be  exposed  by  the 
movements  of  the  lips,  it  may  be  necessary  to  adapt  gum  teeth  (Fig.  936) ; 


Fig.  936. 


Fig.  937. 


if  not,  plain  teeth  are  fitted ;  the  gum  is  to  be  subsequently  formed  of 
pink  vulcanite.  The  teeth  are  to  have  stays  fitted.  The  abutment 
crowns  are  removed  from  the  model,  and  they,  the  teeth,  and  the  plate 
boiled  in  acid.  They  are  returned  to  the  model  and  joined  together  by 
means  of  adhesive  wax  :  a  wire  laid  across  the  backs  from  one  abutment 
crown  to  the  other,  and  covered  by  adhesive  wax,  holds  them  in  position. 
They  are  invested,  and  when  the  investment  is  set  pieces  of  triangular 
wire  are  placed  at  the  junction  of  the  plate  with  the  abutment  crowns, 
and  the  pieces  are  attached  to  one  another  by  means  of  20-carat  solder. 
If  plain  teeth  have  been  employed,  and,  contouring  is  indicated,  a  vul- 
canite gum  is  attached  to  the  plate. 


Porcelain  Bridge-work. 

The  general  plan  and  methods  followed  in  this  class  of  bridge-work 
are  those  of  Dr.  E.  Parmley  Brown,  who  originated  it. 

The  objections  urged  against  bridge-work  composed  of  fine  gold  and 
porcelain  facings  united  by  means  of  fine  solders — that  the  spaces  be- 
tween the  gum  and  the  palatal  surfaces  of  bridge  were  unclean ;  that  the 
oxidation  of  the  base  metals  of  the  solder  permitted  the  accumulation  of 
offensive  materials  ;  and  that  the  porcelain  facings  were,  through  lack  of 
bulk,  in  constant  danger  of  fracture — led  to  the  devising  of  this  method, 
designed  to  overcome  the  several  objections  specified. 

The  bridge  as  made  and  recommended  by  Dr.  Brown  consists  of  a 
rigid  supporting  and  anchoring  bar,  to  which  are  adapted  porcelain  teeth, 
subsequently  united  to  the  bar  and  to  one  another  by  means  of  porcelain 
fused  about  the  parts. 

The  usual  method  of  anchoring  the  bridge  is  by  means  of  arms  ex- 
tending from  the  ends  of  the  bridge,  which  are  anchored  in  cavities 
formed  in  the  natural  teeth  for  their  reception.  Instead  of  what  are 
called  "  self-cleansing  spaces,"  the  base  of  the  bridge  presses  firmly  upon 
the  natural  gum,  with  a  view  to  excluding  even  the  secretions  of  the 
mouth.  A  base-plate  of  iridio-platinum  may  be  accurately  fitted  to  the 
gum,  to  which  the  porcelain  of  the  bridge  is  to  be  attached. 

A  typical  case  for  the  application  of  this  variety  of  bridge  is  that  of 
the  bulkhead — two  cuspid  roots  supporting  six  artificial  crowns.  The 
abutment  roots  are  prepared,  a  platinum  cap  fitted  to  each  ;  the  edges  of 


694 


^.V  ASSEMBLAGE  OF   UNITED   CROWNS. 


the  caps  are  left  projecting  beyond  the  edges  of  the  roots,  then  slit  (Fig. 
938,  A) — bent  over  and  adapted  to  the  walls  of  the  roots  in  the  mouth 


Fig.  938. 


(Fig.  938,  B).  The  root-canals  are  enlarged  and  deep- 
ened, and  metal  posts  filed  to  fit  them  are  placed 
through  openings  made  through  the  caps  into  the 
root-canals.  A  bite  is  taken  ;  then  an  impression  is 
obtained,  in  which  the  caps  and  wires  are  withdrawn. 
An  articulating  model  is  made,  and  facings  selected 
and  ground  into  position.  The  face  of  the  model  is 
varnished  and  oiled,  and  a  plaster  wall  formed  about 
the  teeth  and  model,  holding  the  former  rigidly  in 
position.  A  piece  of  annealed  brass  wire,  three  inches 
long,  has  one  extremity  filed  to  occupy  the  pulp-canal  of  a  cuspid  root  to 
the  depth  it  is  designed  to  carry  the  anchoring  bar ;  the  wire  above  the 
cap  is  flattened  to  a  distance  which  shall  permit  perforating  it  for  the 
reception  of  the  pins  for  the  cuspid  teeth.  The  wire  is  bent  at  right 
angles,  then  carried  across  the  posterior  surfaces  of  the  incisor  crowns ; 
it  is  to  occupy  the  space  between  the  pins  of  these  teeth.  Above  the 
upper  pin  of  the  opposite  cuspid  crown  it  is  again  bent  at  right  angles ; 
the  lower  end  is  shortened  to  adjustment  with  the  depths  of  the  pulp- 
canal.  This  wire  forms  a  pattern  which  is  reproduced  in  iridio-platinum 
wire  from  13  to  15  gauge,  which  is  annealed  and  flattened  so  that  a  por- 
tion of  it  will  present  a  flat  surface  to  the  backs  of  the  cuspids,  and  the 
transverse  portion  flattened  to  rest  upon  the  backs  of  the  incisors  be- 
tween the  pins.  The  wire  is  bent  to  the  conformation  of  the  brass  wire 
pattern  (Fig.  939). 

The  caps  over  the  root-faces  are  loosened,  returned  to  position, 
and  the  iridium  bar  set  in  position.  The  wall  holding  the  porce- 
lain facings    is  applied,  and  the    perpendicular   arms  of  the    flattened 


Fig.  939. 


Fig  940 


Porcelain  metal  band. 


wire  perforated  for  the  passage  of  the  pins  of  the  cuspid  crowns.  The 
wall  is  removed,  the  bar  is  cemented  to  the  caps,  and  these  and  the  bar 
withdrawn  from  the  model  invested  and  soldered  with  the  minimum  of 
pure  gold.  The  piece  and  teeth  are  boiled  in  a  1  : 3  sulphuric-acid  solu- 
tion. The  bar  and  caps  are  set  in  position  on  the  model.  The  teeth  are 
returned  to  the  plaster  wall,  the  pins  of  the  cuspid  crowns  passing 
through  the  perforations  in  the  bar.  The  pins  of  the  incisor  crowns  are 
bent  over  the  bar,  holding  each  tooth  in  position.  The  wire  may  be 
grooved  or  notched  at  the  site  of  the  pins  to  form  retaining  slots.  The 
piece  is  now  carefully  lifted  from  the  model  and  prepared  for  the  appli- 
cation of  the  porcelain  (Fig.  940). 


FOR  CELA  IN  BR  ID  GE-  WORK. 


695 


Depressions  are  made  in  a  fire-clay  slab  which  shall  support  the  bars 
and  the  teeth.  Porcelain  body,  made  into  a  paste  with  water,  is  applied, 
giving  a  contour  in  consonance  with  the  articulation  and  the  contact  with 
the  soft  tissues.  The  body  is  applied  as  the  second  body  of  a  continuous- 
gum  piece.  It  is  set  on  the  supporting  slab,  and  the  porcelain  fused  in 
a  proper  furnace,  as  with  continuous-gum  pieces. 

Gum  contour  of  similar  cases  may  be  restored  after  the  following 
method  :  Caps  are  fitted  to  the  prepared  cuspid  roots  as  for  the  preceding 
case.  A  pair  of  cuspid  facings  are  selected,  and  also  four  incisors  of  the 
continuous-gum  variety.  The  cuspid  caps  are  set  in  position  and  an 
impression  in  modelling  compound  taken,  which  presses  firmly  upon  the 
anterior  gum.  A  model  of  investing  material,  and  next  dies,  are  made, 
and  an  iridio-platinum  plate  No.  32  is  swaged.  This  plate  should  extend 
upon  the  outer  alveolar  wall  as  high  as  it  is  desired  to  have  the  artificial 
gum.     At    its  palatal  aspect  the  edge  should  be    formed  to  represent 


Fig.  941. 


Fig.  942. 


about  the  usual  neck  sections  of  natural  incisors.  The  lateral  edges  of 
the  plate  should  overlap  or  lie  firmly  against  the  sides  of  the  cuspid  col- 
lars, to  which  it  is  united  by  means  of  a  small  amount  of  24-carat  gold 
as  solder.  The  piece  is  transferred  to  the  mouth ;  wire  posts  the  size  of 
the  canals-are  fitted ;  a  bite  and  next  a  plaster  impression  are  taken.  A 
model  of  investing  material  is  made  and  an  articulator  mounted. 

The  porcelain  teeth  are  now  adjusted  to  position ;  the  incisors,  as 
though  for  the  usual  continuous-gum  operations,  and  their  stays  are 
fitted  to  the  teeth  ;  a  support  and  posts  of  the  form  previously  described 
are  adapted,  over  which  the  pins  of  the  incisors  crowns  are  bent  (Fig.  941). 
More  investing  material  is  applied  to  cover  and  jirotect  the  porcelain,  and 
the  teeth  are  united  to  the  bar  and  stays,  and  the  posts  to  the  collars  by 
means  of  the  minimum  of  24-carat  solder.  Fig.  942  shows  labial  aspect. 
The  porcelain  is  next  added.  Sufficient  body  is  applied  to  give  the 
desired  contour,  the  piece  is  baked,  and  the  gum  enamel  is  then  added 
and  a  final  baking  given. 

Porcelain  bridges  for  the  replacement  of  the  bicuspids  and  molars 
may  be  constructed  after  the  same  method. 

Fig.  903  illustrates  a  typical  case.  A  plate  is  swaged,  being  only  of 
sufficient  size  to  support  the  bases  of  the  teeth  and  the  artificial  gum. 
When  the  plate  abuts  the  natural  teeth  a  surplus  of  metal  is  left.  The 
teeth  are  adapted  and  the  post  and  bar  support  formed.     The  teeth  are 


696 


AN  ASSEMBLAGE  OF  UNITED   CROWNS. 


to  have  their  stays  adapted.     The  ends  of  the  plate  are  burnished  about 
the  bar,  and  the  pins  are  next  bent  down,  holding  the  teeth  in  position 


Fig.  943. 


(Fig.  944).  The  piece  is  detached  from  the  model,  invested,  and  sol- 
dered by  means  of  24-carat  plate.  The  porcelain  is  to  be  added  as  in 
the  preceding  case.     Fig.  945  shows  the  finished  case. 


Fig.  944. 


Fig.  945. 


Figs.  946  and  947  illustrate  the  application  of  porcelain  bridge-work 
to  a  common  class  of  cases.     A  pulpless  central  incisor,  which  has  not 


Fig.  946. 


Fig.  947. 


Fig.  948. 


lost  too  much  of  its  substance  through  the  invasion  of  caries,  and  whose 
crown  has  not  discolored,  a  cuspid  which  may  contain  a  vital  pulp  or  be 
pulpless,— these  serve  as  the  abutments.  The  anchorage  in  the  cuspid, 
if  it  contain  a  vital  pulp,  should  not  be  deep  enough  to  endanger  that 
organ,  and  yet  should  be  sufficiently  deep  to  ensure  immobility  of  the 
bridge  when  anchored  by  a  filling  of  cohesive  gold. 


SETTING  BRIDGES.  697 

Fig.  948  illustrates  a  bridge  for  a  similar  case,  in  which  the  crown 
of  the  central  incisor  is  too  frail  to  successfully  resist  the  stress  of  mas- 
tication, or  which  has  lost  so  much  of  its  substance  that  decrowning  is 
the  indication  for  aesthetic  considerations. 

Setting  Bridges. 

Before  cementing  a  bridge  to  its  abutments  it  is  tried  to  them,  and, 
should  any  points  interfere  with  its  ready  placement,  they  are  cut  or 
ground  away  until  the  piece  may  be  slipped  into  position  with  easy 
facility.  When  the  abutment  crowns  are  of  the  barrel  type,  a  minute 
opening  is  made  in  the  sulcus  of  each  crown. 

The  zinc  phosphate  used  for  bridge-setting  should  be  moderately  slow 
setting ;  it  should  remain  plastic  long  enough  to  permit  the  deliberate 
and  careful  setting  of  the  bridge  ;  should  flow  freely  even  through  almost 
microscopic  openings ;  should  harden  in  about  fifteen  minutes  with  a 
glazed  surface ;  should  quickly  lose  an  acid  reaction.  In  an  hour  it 
should  be  extremely  hard,  and  it  is  of  great  importance  that  it  should  be 
but  slightly  soluble.  Fresh  specimens  of  bridge  cement  are  to  be  tested 
to  see  that  they  answer  these  requirements. 

For  setting  the  variety  of  bridge  mentioned,  a  few  large  drops  of 
the  cement  fluid  are  placed  on  a  clean  mixing  slab,  and  beside  it  an 
excess  of  powder.  Powder  is  gradually  and  thoroughly  incorporated 
with  the  fluid  until  a  paste  is  made  which  drops  reluctantly  from  the  tip 
of  the  spatula.  The  paste,  as  it  is,  is  carried  into  the  deepest  p^  rtions  of 
the  crowns.  The  abutment  teeth,  having  been  washed  with  chloroform 
to  remove  any  fatty  deposits  and  to  dry  them  by  its  evaporation,  are 
protected  by  napkins ;  the  bridge  is  quickly  carried  into  place  and  steadily 
pressed  into  its  position.  The  napkin  is  removed  and  a  piece  of  heavy 
tin-foil  is  laid  over  the  entire  masticating  surface  of  the  bridge,  and  the 
patient  directed  to  close  the  teeth  against  it,  and  to  keep  them  closed 
for  twenty  minutes.  Patients  should  receive  explicit  injunctions  not  to 
masticate  upon  a  bridge  for  at  least  two  hours  after  it  has  been  set. 

In  setting  bridges,  one  or  more  of  the  abutment  crowns  of  which  are 
post  crowns,  the  canals  of  the  teeth  should  be  cleansed  with  hydrogen 
peroxide  and  dried  by  means  of  alcohol  and  a  hot  blast.  A  wisp  of  cot- 
ton containing  25  per  cent,  pyrozone  is  passed  around  the  neck  of  each 
root ;  this  will  prevent  exudation  and  keep  the  root  free  from  the  con- 
tact of  secretions  until  the  collars  are  set  in  position.  The  cement  is 
made  slightly  thinner  for  setting  such  crowns :  the  concavities  of  the 
crowns  are  filled  with  cement,  a  portion  placed  in  the  root-canal,  and 
the  bridge  is  carried  into  place  when  the  occlusion  is  tested,  the  tin-foil 
between  the  teeth  as  before. 

In  setting  a  bridge,  one  abutment  of  Avhich  is  a  bar  anchorage 
to  have  a  metallic  filling  built  around  it,  no  attempt  should  be  made 
toward  making  the  filling  until  the  cement  about  the  other  abutments  is 
rigid.  It  is,  however,  a  wise  precaution  to  place  a  layer  of  amalgam 
upon  the  floor  of  the  cavity  before  the  bridge  is  adjusted,  and  then 
press  the  bar  into  the  amalgam.  A  better  practice  is  to  line  the  cavity 
with  filling  material,  shaping  a  cavity  in  it  to  engage  the  bar,  and  finish- 
ing the  margins  before  setting  the  bridge.  Then,  Avhen  the  cement  of 
the  other  abutments  has  set,  the  filling  about  the  bar  is  Completed  with 


698  AN  ASSEMBLAGE   OF   UNITED   CROWNS. 

cohesive  foil  malleted  about  it,  holding  it  firmly.  When  perfect  dryness 
can  be  maintained  rolled  foil  No.  30  is  annealed  and  packed  with  a 
mallet. 

In  setting  double-bar  bridges  the  thinnest  of  rubber  dam  is  adjusted, 
the  cavities  prepared,  and  the  bridge  set  in  position ;  the  portions  of  the 
cavity  which  would  be  made  inaccessible  by  placing  the  bars  are  filled 
as  a  preliminary  measure — filled  a  little  more  than  necessary  ;  then  slots 
cut  in  them  which  shall  engage  the  edges  of  the  bars,  and  the  edges  of 
the  filling  filed  flush  with  the  cavity  margins.  The  bridge  is  set  in 
position,  and  cohesive  foil  malleted  about  and  over  the  bar,  completing 
one  filling.  During  the  packing  of  the  gold  the  bridge  has  been  held 
rigidly  in  position  with  the  left  hand.  If  the  veneer  filling  has  been 
properly  shaped,  it  almost  retains  the  bridge  of  itself  during  the  pack- 
ing of  the  gold.  The  second  filling  is  completed  in  the  same  manner, 
and  both  are  trimmed  and  polished.  The  rubber  dam  is  stretched,  and 
a  cut  made,  joining  the  openings  embracing  the  abutment  teeth,  and  is 
removed. 

The  Repair  of  Bridge-work. 

The  difficulty  of  properly  repairing  bridge-work  is  one  of  the  objec- 
tions persistently  urged  against  it  since  its  introduction.  Any  accidents 
to  removable  bridges  are  readily  remedied  by  detaching  the  pieces  and 
repairing  in  the  same  manner  as  the  individual  part  was  originally  con- 
structed. The  common  accident  affecting  fixed  bridges  is  fracture  of  a 
porcelain  facing.  This  occurs  usually  in  consequence  of  the  porcelain 
facings  being  improperly  or  insufficiently  protected  from  the  direct  stress 
of  mastication,  and  not  infrequently  by  the  tooth  being  split  in  one  of  the 
soldering  operations.  If  the  dummies  and  facings  have  been  properly 
constructed,  made  from  strong  teeth,  and  due  care  exercised  in  soldering^ 
porcelain  facings  should  never  break,  as  they  are  never  subjected  to  stress. 

To  accurately  replace  a  broken  facing  or  to  remedy  any  marked 
defect  of  a  bridge  piece,  it  is  in  the  majority  of  cases  necessary  to 
remove  it  from  its  abutments.  If  the  abutment  crowns  are  of  the  bar- 
rel variety,  it  is  usually  necessary  to  split  the  barrels  to  effect  their 
removal.  By  means  of  a  fine  hatchet  excavator  the  crown  is  marked 
from  its  edge  to  its  cutting  surface  by  a  gradually  deepening  groove 
made  in  its  buccal  wall.  When  the  gold  is  cut  through  a  fine  instru- 
ment is  passed  into  the  cut  and   the  cement  detached  piecemeal. 

The  crown  may  be  quickly  split  by  means  of  the  cap  crown-slitter 
(Fig.  949).  An  effort  is  now  made  to  loosen  and  detach  the  bridge  Avith- 
out  splitting  the  second  cap  ;  if  this  is  not  possible,  it  is  also  divided  at 
its  buccal  wall.  Should  one  abutment  crown  be  of  the  post-and-collar 
variety,  a  drill  is  passed  through  the  palatal  side  of  the  cap,  severing  its 
attachment  to  the  post.  A  square-edged  instrument  is  passed  above  the 
edge  of  the  collar,  and  traction  in  all  directions  is  exerted  until  the 
bridge  is  detached.  It  may  be  necessary  to  divide  the  collar  of  this 
abutment  also  :  this  is  done  at  the  palatal  side.  Should  it  be  the  facing 
over  a  post  crowm  that  has  broken,  the  division  of  the  post  from  the  cap 
may  be  made  through  the  angle  at  the  base  of  the  stay ;  however,  the 
perforation  through  the  back  should  be  made  also  for  the  introduction 
of  the    new  post.     The  case  is  boiled  in  strong  nitric  acid,  which  will 


THE  REPAIR   OF  BRIDGE-WORK. 


699 


The  sections  of  the 
Fig.  949. 


dissolve  the  old  cement  and  cleanse  every  crevice, 
crowns  are  bent  back  into  their  orig- 
inal positions,  and  the  post  removed 
from  the  root,  as  described  in  Chapter 
XVIII. 

Along  the  cuts  of  the  crowns,  in 
their  interiors,  small  strips  of  thin 
platinum  are  attached  by  means  of 
flux  wax.  The  bridge  is  set  in  posi- 
tion in  the  mouth ;  a  new  post  is 
passed  into  the  root-canal  of  the  ante- 
rior abutment  through  the  opening  in 
the  cap  made  for  its  passage ;  the 
end  of  the  post  is  to  extend  beyond 
the  opening.  A  bite  is  taken  if 
necessary,  and  an  impression ;  a  cast 
is  made  of  investing  material.  A 
porcelain  facing  is  fitted  to  the  cap 
as  described  in  Chapter  XVIII. 
(Repairing  Crowns). 

A  porcelain  dummy  to  be  re- 
placed is  adjusted  in  the  following 
manner  :  A  dummy  the  size  and  shape 
of  the  one  broken  is  selected ;  a 
spear-pointed  drill  is  passed  through 
the  backing  and  gold  body  in  the 
positions  of  the  pins  ;  these  openings 
are  enlarged  to  easily  receive  the 
pins  of  the  facing,  A  deep  gutter 
is  cut,  burred  away  between  the 
holes  on  the  palatal  side  until  the 
platinum  pins  protrude  through  them, 
when  the  facing  is  ground  in.  A 
thin  layer  of  gold  is  scraped  away 
from  the  backing,  and  the  facing 
backed  with  very  thin  platinum. 
The  surface  of  this  stay  and  that  of 
the  gold  with  which  it  is  in  contact 
are  covered  with  borax,  and  the  fac- 
ing set  in  position  and  held  by  means 
of  adhesive  wax  melted  over  the  ends 
of  the  pins. 

The  porcelain  surfaces  are  covered 
with  investment  material,  all  the 
parts  to  be  soldered  left  uncovered. 
The  wax  is  removed,  and  the  cast 
cut  away  to  fully  expose  the  gum 
edge  of  the  platinum  stay.  A  large 
piece  of  14-carat  solder  is  placed  over 
each  pin  and  a  piece  at  the  line  of 
juncture  between  the  platinum  stay  and  the  gold  block,  and  over  all 


Cap-crown  slitter. 


700  AN  ASSEMBLAGE  OF  UNITED  CROWNS 

other  parts  to  be  joined  additional  pieces  are  placed.  The  casse  is  heated : 
a  fine  flame  is  directed  against  the  investment,  and  when  the  porcelain 
is  red  hot  a  touch  of  the  flame  will  fuse  the  solder  over  the  line  of 
division  of  the  barrel  crown.  The  investment  quickly  turned  over, 
the  flame  directed  against  the  solder  at  the  base  of  the  dummy  stay 
will  fuse  the  solder  there  and  that  placed  over  the  pins ;  it  will!  run 
through  and  fill  the  spaces  between  the  parts.  The  soldering  of  the 
anterior  abutment  crown  is  next  done. 

This  general  method  applies  for  all  thorough  repairs  to  bridge  pieces. 

The  difficulty  of  removing  bridges,  the  dangers  of  irremediable  muti- 
lation, and  the  necessary  expense  attending  such  a  complicated  repair 
have  led  to  the  devising  of  many  methods  for  repairing  while  the  bridge 
is  in  position  without  detaching  it. 

One  of  the  methods  is  that  of  Dr.  Mason,  described  in  Chapter 
XVIII.,  where  a  removable  porcelain  facing  has  been  used,  anticipating 
possible  fracture. 

If  a  facing  of  one  of  the  anterior  teeth  should  be  fractured,  the  pins 
are  cut  from  the  backing ;  a  new  facing  corresponding  with  the  old  one 
is  selected  ;  its  pins  are  to  have  their  edges  touched  with  a  mixture  of 
olive  oil  and  vermilion,  which  marks  the  backings ;  holes  are  drilled 
through  the  backing  by  means  of  a  spear-pointed  drill,  and  are  coun- 
tersunk at  their  palatal  sides.  The  tooth  is  to  receive  any  grinding 
necessary  to  adapt  it  to  the  backing,  and  the  pins  are  riveted  in  the  fol- 
lowing manner :  One  arm  of  a  pair  of  plate  punch -forceps  is  covered 
by  a  concave  block  of  lead  which  rests  upon  the  labial  surface  of 
the  facing.  The  other  jaw  is  armed  with  a  broad  punch,  and  between 
them  the  platinum  pins  are  compressed  into  the  countersinks,  filling 
them  and  forming  rivet  heads.  The  heads  are  rounded  by  means  of 
burnishers. 

A  method  of  replacing  a  molar  or  bicuspid  facing  is  as  follows : 

Holes  are  drilled  through  the  backing,  and  at  their  palatal  aspects  are 

elongated  divergingly.     A  facing  is  adapted  to  its  surface  and 

Fig.  950.     the  pins  covered  with  zinc  phosphate,  and  it  is  pressed  into 

~  position ;  the  pins  are  immediately  separated,  being  jaressed 

against  the  far  walls  of  the  slots.     When  the  cement  has  set 

any  excess  of  pin  or  cement  is  removed. 

Prof.  E.  T.  Darby  suggests  a  method  which  he  has  found 
to  serve  well :  A  cross-pin  facing  is  selected.  A  slot  is  cut  in  the  metal 
backing  by  means  of  burs,  giving  the  cavity  a  pyramidal  form,  as  in  the 
Mason  backing,  its  small  end  external.  A  metallic  bar  is  soldered  to 
the  tips  of  the  pins,  which  have  been  bent  to  diverge  slightly,  uniting 
them ;  the  facing  so  prepared  is  cemented  in  the  cavity  made  in  the 
backing. 

Dr.  Emory  A.  Bryant^  describes  a  novel  and  effective  method  of 
attaching  a  new  facing.  A  tap  and  die  the  size  of  tooth-pins  are  neces- 
sary, together  with  a  special  countersinking  tool  and  a  screw-driver 
(Figs.  951  to  954).  The  pins  are  cut  from  the  old  backing,  and  holes 
are  drilled  the  size  of  the  pins  of  the  new  facing,  and  in  the  proper  posi- 
tions. With  the  countersinking  tool  held  in  a  right-angled  hand  piece, 
the  holes  are  countersunk  exactly  to  the  outer  wall  of  the  backing — no 
^  Cosmos,  vol.  xxxvi.  p.  469  et  seq. 


THE  REPAIR   OF  BRIDGE-WORK. 


701 


more,  no  less.  The  nuts  are  made,  or  have  been  made,  the  size  of  the 
countersink.  By  means  of  the  oiled  die  a  thread  is  cut  on  the  pin  of 
each  tooth,  exercising  great  care  that  the  pins  are  not  twisted,  the  thread 


Fig.  951. 


Fig.  952. 


Fig.  953. 


Fig.  954. 


Fig.  955. 


to  be  continued  to  the  back  of  the  facing.  Nuts  are  tried  on  each  of  the 
threaded  pins,  and  marked  to  denote  the  pins  they  fit.  The  facing  is  set 
in  position,  and  each  nut  is  loosely  adjusted,  then  alternately  screwed  into 
place,  drawing  the  facing  close  to  the  stay.  The  protruding  portions  of 
nut  and  pin  are  ground  down  and  polished.  Dr.  Bryant  states  that  this 
substitution  may  be  made  in  twenty-five  minutes. 


CHAPTER   XX. 

HYGIENIC  RELATIONS  AND  CARE  OF  ARTIFICIAL 
DENTURES. 

By  Charles  J.  Essig,  M.  D.,  D.  D.  S. 


There  can  hardly  be  room  for  doubt  that  a  well-planned  and  prop- 
erly adjusted  artificial  denture  contributes  to  comfort  and  health,  and 
prolongs  the  life  of  the  individual  who  by  reason  of  premature  loss  of 
the  natural  teeth  finds  it  necessary  to  wear  one,  but  the  usefulness  of  the 
fixture  and  its  influence  on  the  mind  and  general  health  of  the  patient 
depend  very  largely  upon  the  manner  in  which  it  is  planned  and  con- 
structed. It  may  be  made  an  instrument  of  discomfort,  if  not  of  torture, 
by  constructing  it  upon  a  faulty  impression.  It  may  entirely  fail  to 
meet  the  demands  of  a  masticating  apparatus  by  imperfect  articulation 
of  the  teeth.  It  may  so  interfere  with  speech,  through  want  of  adhesion, 
that  the  wearer  is  at  all  times  conscious  of  its  presence,  and  he  is  thus 
sometimes  forced  to  give  up  social  intercourse,  or  if,  as  in  the  case  of 
lawyers  or  clergymen,  professional  duties  require  the  individual  to  ad- 
dress audiences,  the  patient  feels  that  his  usefulness  is  abridged,  and 
mental  depression  and  departure  from  a  normal  standard  of  health 
follow. 

Prosthetic  dentistry  requires  in  its  successful  practice  good  judgment, 
artistic  taste,  and  a  high  degree  of  manipulative  ability.  Xo  two  cases 
are  ever  precisely  alike,  and  each  one  demands  careful  study  and  a 
definite  plan  of  procedure.  The  choice  of  material,  means  of  attach- 
ment, style  of  teeth,  and  the  arrangement  of  the  latter  to  ensure  the 
greatest  attainable  degree  of  efficiency  in  mastication  are  to  be  con- 
sidered. 

With  the  materials  at  the  present  time  within  the  reach  of  every 
prosthetic  dentist,  and  the  light  of  the  experience  of  other  workers  in 
that  branch  in  the  recent  past,  it  is  not  claiming  too  much  to  say  that 
artificial  dentures  may  be  so  constructed  and  adjusted  to  any  or  all 
mouths  as  to  restore  the  functions  of  mastication  and  speech,  as  well  as 
natural  appearance,  in  a  manner  but  little  short  of  absolute  perfection. 

The  hygienic  conditions  incident  to  the  use  of  artificial  dentures  may 
be  local  or  systemic.  Many  morbid  phenomena  of  a  local  character  may 
be  observed  as  resulting  from  their  presence,  and  marked  constitutional 
disturbances  have  been  traced  to  the  causes  above  alluded  to,  as  well 
as  those  arising  from  long-maintained  local  irritation  caused  by  mal- 
adaptation  or  the  unsuitable  character  of  the  materials  used  in  their 
construction. 
702 


ARTIFICIAL  DENTURES.  703 

In  the  insertion  of  an  artificial  denture  a  foreign  body  is  introduced 
into  the  oral  cavity  which  may  act  as  an  irritant  to  tissues  and  organs 
with  which  it  comes  in  contact.  This  is  particularly  liable  to  occur  in 
all  lower  dentures,  on  account  of  the  pressure  being  confined  to  a  nar-- 
rower  area  and  the  muscles  and  integuments  being  attached  well  toward 
the  top  of  the  ridge,  as  in  the  case  of  the  buccinator  muscles ;  painful 
abrasions  frequently  result  in  this  class  of  cases  soon  after  the  introduc- 
tion of  the  fixture.  Abrasions  produced  by  undue  pressure  of  the  edge 
of  a  plate  cause  an  amount  of  discomfort  and  suffering  entirely  out  of 
proportion  to  the  extent  of  the  injury.  To  avoid  a  continuance  of  this 
trouble  and  to  give  immediate  relief  the  patient  should  always  be  cau- 
tioned to  return  the  moment  the  presence  of  the  denture  becomes  painful. 

Artificial  dentures  are  held  in  place  by  atmospheric  adhesion,  by 
clasps,  by  spiral  springs,  or  by  permanent  or  immovable  attachments  to 
natural  teeth  or  roots.  Either  of  these  may  become  the  cause  of  irrita- 
tion to  the  teeth  or  contiguous  parts.  In  the  case  of  clasps  the  tendency 
invariably  is  to  produce  morbid  phenomena,  and  this  tendency  is  in- 
creased or  lessened  by  the  character  of  the  materials  of  which  they  are 
made,  and  the  manner  in  which  the  clasjDS  are  adjusted  and  the  parts  of 
the  teeth  embraced  by  them. 

The  result  produced  by  clasping  natural  teeth  is  a  loss  of  tissues, 
either  through  caries,  mechanical  abrasion,  electro-chemical  action,  or  by 
the  joint  action  of  all  three.  The  rapidity  with  which  the  disintegrat- 
ing process  advances  depends  largely  upon  the  quality  of  the  tooth-sub- 
stance, the  condition  of  the  oral  fluids,  the  size  and  form  of  the  clasp, 
the  portion  of  the  tooth  which  is  embraced  by  it,  and  the  material  of 
which  the  clasp  is  constructed. 

A  partial  lower  denture  must  be  secured  either  by  clasps  or  contact 
with  natural  teeth.  In  that  class  of  partial  lower  dentures  designed  to 
replace  the  second  bicuspids  and  molars  on  each  side  clasps  adjusted  to 
the  first  bicuspids  are  generally  employed  :  caries  of  the  approximate 
surfaces  of  the  first  bicuspids  is  more  or  less  quickly  induced,  probably 
because  the  enamel  is  thin  at  that  point.  Incipient  caries,  produced  by 
clasps  at  the  positions  above  indicated,  manifests  itself  by  great  sensitive- 
ness of  the  tooth,  which  is  exceedingly  painful  when  exposed  to  extremes 
of  temperature  and  certain  kinds  of  food,  such  as  very  sweet  or  salt  arti- 
cles. Painful  mechanical  abrasions  are  frequently  caused  where  mere 
contact  with  natural  teeth  is  the  means  adopted  for  securing  stability  to 
partial  dentures.  Badly-fitting  clasps,  as  may  be  expected,  rapidly 
hasten  the  progress  of  caries  by  favoring  the  lodgement  between  the 
tooth  and  clasp  of  particles  of  food  mixed  with  the  oral  fluids,  which 
undergo  fermentative  decomposition  and  produce  agents  destructive  to 
the  enamel  and  dentine. 

Clasps  should  be  accurately  fitted  to  the  broadest  part  of  the  tooth, 
which  is  usually  found  at  or  near  the  masticating  portion  of  the  crown, 
and  never  at  the  necks  of  the  tooth.  They  should  not  be  allowed  to 
impinge  upon  the  gum,  as  recession  of  that  tissue  and  exposure  of  the 
cementum,  with  subsequent  softening  and  caries,  will  almost  certainly 
supervene. 

In  addition  to  the  liability  to  caries  alluded  to,  the  author  has 
observed  that  when  clasps  are  fitted  to  bicuspids  for  the  purpose  of  re- 


704  RELATIONS  AND   CARE  OF  ARTIFICIAL  DENTURES. 

taining  partial  lower  dentures  in  situ,  those  teeth  are  very  liable  to  be 
loosened  and  speedily  lost  by  the  strain  brought  to  bear  upon  them  dur- 
ing mastication.  For  these  reasons  he  has  abandoned  clasps  in  this  class 
■of  cases  wherever  possible,  using  instead  the  outside  bar  shown  on  page 
344. 

The  result  of  observation  as  to  the  eifect  of  clasps  upon  the  natural 
teeth  is  undoubtedly  in  all  cases  unfavorable,  yet  there  are  many  in- 
stances in  which  clasps  are  indispensable  ;  but  their  capacity  for  doing 
harm  may  be  very  greatly  reduced  by  adjusting  them  with  accuracy  to 
the  most  convex  portions  of  the  teeth,  avoiding  impingement  upon  the 
necks  and  cementum. 

It  has  been  observed  that  clasps  exert  an  influence  upon  teeth  vary- 
ing in  degree  according  to  the  condition  of  the  oral  fluids  and  the  kind 
of  metal  of  which  they  are  made.  Silver  clasps  have  been  found  to 
exert  a  much  more  rapid  disintegrating  influence  than  those  made  of 
gold.  Dentures  with  clasps  or  attachments  made  of  platinum  or  iridio- 
platinum  act  more  injuriously  than  the  same  appliances  fitted  with  gold 
clasps.  These  difi'erences  in  the  effects  of  the  metals  upon  the  teeth  are 
undoubtedly  due  to  a  galvanic  current  between  the  tooth-structure  and 
the  metal  forming  the  plate,  aided  by  certain  conditions  of  the  oral  fluids. 

Silver  and  platinum  should  not  be  used  in  the  formation  of  clasps,  or 
indeed  for  any  purpose  which  demands  contact  with  tooth-structure.  It 
has  been  observed  that  platinum  wire  when  employed  as  a  means  of 
retaining  teeth,  the  positions  of  which  had  been  changed  in  the  cor- 
rection of  irregularities,  showed  erosions  in  a  comparatively  short  time 
after  its  application. 

An  example  of  the  action  of  silver  upon  the  natural  teeth  was 
observed  a  number  of  years  ago  in  the  case  of  a  man  who  had  in  an 
election  fracas  sustained  a  severe  fracture  of  the  jaw.  When  he  pre- 
sented himself  for  treatment  at  the  college  clinic,  nearly  a  year  after 
the  injury  had  been  received,  it  was  found  that  the  jaw  was  in  three 
parts,  no  union  having  taken  place.  He  had  received  a  blow  from  some 
heavy  instrument  upon  the  mental  portion  of  the  bone  ;  the  fractures 
were  on  each  side  between  the  first  and  second  bicuspids.  The  individ- 
ual, for  some  reason  best  known  to  himself,  had  been  obliged  to  remain 
in  concealment  for  several  weeks  after  the  injury,  during  which  time  he 
received  no  surgical  treatment  whatever.  The  appearance  of  the  lower 
part  of  the  face  was  greatly  changed  by  the  displacement  of  the  disunited 
parts  of  the  jaw,  and  mastication  was  impossible.  As  a  temporary  or 
palliative  remedy  for  the  latter  difliculty  a  dental  surgeon  had  fitted  a 
bar  of  stout  half-round  silver  wire  entirely  around  the  lower  teeth,  so  as 
to  hold  the  parts  in  juxtaposition  and  restore  the  articulation  of  the 
teeth.  The  individual  had  not  worn  the  fixture  many  weeks  before  the 
posterior  surfaces  of  the  second  molars,  where  the  brunt  of  the  force  was 
borne,  became  unbearably  sensitive.  An  examination  showed  deep  grooves 
in  these  teeth,  rapidly  approaching  the  pulps.  As  the  neighboring  teeth 
appeared  of  good  quality  and  entirely  free  of  caries,  the  abrasion  on  the 
second  molars  was  probably  due  to  galvanic  action  between  the  silver 
support  and  the  tooth-structure. 

The  wearing  of  artificial  dentures  at  night  is  a  subject  upon  which 
there  is  much  difiference  of  opinion  :  there  is  hardly  room  for  doubt, 


HYGIENIC  RELATIONS.  705 

however,  that  disintegration  of  the  tooth -substance  when  clasps  are  used 
IS  likely  to  proceed  much  more  rapidly  where  the  piece  is  worn  con- 
tmuously;  besides,  careful  observation  has  shown  that  at  night  the 
oral  secretions  assume  a  slightly  acid  character.  This  has  been  demon- 
strated particularly  in  patients  subject  to  enamel  erosion  by  carefully 
testmg  the  oral  secretions  with  litmus  after  waking  and  before  the  sali- 
vary fluids  have  started  their  usual  flow. 

If  the  necks  of  the  teeth  are  highly  sensitive  or  there  is  well-marked 
tendency  to  softening  or  erosion  of  the  tooth-structure,  the  patient  should 
be  directed  to  remove  the  plate  each  night  before  retiring,  and  to  apply 
to  the  affected  teeth,  after  thoroughly  cleansing,  a  small  quantity  of  pre- 
cipitated chalk,  lime-water,  or  milk  of  magnesia. 

Too  much  stress  cannot  be  laid  upon  the  necessity  for  cleanliness,  and 
every  patient  who  wears  a  denture  secured  by  clasps  should  be  partic- 
ularly instructed  in  the  means  of  removing  the  deposits  which  are  usually 
found  on  the  inside  surfaces  of  the  clasps.  This  is  not  generally  well 
done  by  patients  with  the  tooth-brush  alone,  so  that  a  piece  of  soft  wood 
armed  with  fine  pumice  is  necessary  to  do  it  thoroughly,  and  the  addi- 
tion of  aqua  ammonia  is  efficacious. 

Patients  suffering  from  any  chronic  conditions  of  the  system  which 
are  likely  to  be  accompanied  with  acidity  of  the  oral  fluids  must  be  cau- 
tioned to  exercise  the  most  scrupulous  care  in  cleansing  the  artificial 
denture;  and  this  caution  is  particularly  demanded  when  partial  dentures 
are  worn.  In  these  cases  lime-water  and  bicarbonate  of  sodium  are  re- 
commended as  alkaline  mouth-washes,  which  by  neutralizing  the  acid 
condition  of  the  fluids  are  often  effective  in  preventing  sensitiveness  and 
the  tendency  to  softening  of  the  tooth-substance. 

In  attaching  clasps  to  the  elongated  molar  teeth  of  elderly  patients 
the  clasps  should  be  arranged  so  that  no  broad  metallic  surface  will  be 
in  contact  with  the  exposed  neck  of  the  tooth. 
This  may  be  accomplished  by  attaching  the  clasp 
to  the  plate  by  two  narrow  posts,  as  shown  in 
Fig.  956. 

In  the  mouths  of  young  persons  whose  teeth 
show  unmistakable  evidences  of  a  tendency  to 
rapid  decalcification  clasps  should  never  be  em- 
ployed ;  and  this  is  a  matter  to  be  decided  by  the 
dentist  himself  even  when  the  patient  expresses 
the  strongest  preference  for  the  small  plate  attached  by  clasps  and  an 
equally  forcible  objection  to  the  larger  atmospheric  plate. 

Of  the  hygienic  relations  of  spiral  springs,  which  as  a  means  of  re- 
taining artificial  dentures  antedated  all  other  devices  now  in  use,  very 
little  need  be  said,  since  the  appliances  are  no  longer  used  except  in  rare 
cases  of  edentulous  mouths  complicated  with  cleft  palate,  wherein  atmo- 
spheric adhesion  would  be  impossible.  Three  principal  objections  may 
be  urged  against  the  employment  of  spiral  springs  for  theretention  of 
ordinary  dentures,  as  follows:  their  liability  to  chafe  and  abrade  the 
delicate  mucous-membrane  lining  of  the  cheek,  the  tendency  of  one  or 
the  other  to  break,  and  the  difficulty  of  thoroughly  cleaning  them. 

The  materials  used  in  the  construction  of  artificial  dentures,  other 
conditions  being  equal,  do  not  differ  to  any  great  extent  in  their  effect 

45 


706  RELATIONS  AND   CARE  OF  ARTIFICIAL  DENTURES. 

upon  the  tissues  with  which  they  come  in  contact.  On  the  other  hand, 
the  frequency  and  extent  of  oral  irritation  associated  with  the  wearing 
of  artificial  dentures,  irrespective  of  materials  employed,  varies  with  dif- 
ferent individuals.  It  is  not,  however,  denied  that  modifications  of  that 
portion  of  the  surface  of  the  mouth  covered  by  the  artificial  denture  is 
more  frequent  in  cases  where  rubber  and  celluloid  are  worn.  The  author 
has  always  believed  that  the  real  cause  of  the  inflammatory  condition  so 
generally  attributed  to  vegetable  bases  will  be  found  in  the  following 
conditions  :  (1)  The  non-conducting  quality  of  the  substances ;  (2)  the 
rough  condition  of  the  surfaces  of  the  majority  of  rubber  or  celluloid 
dentures,  due  to  carelessness  or  want  of  skill  in  construction ;  (3)  want 
of  care  on  the  part  of  the  wearer  in  not  frequently  cleansing  the  denture 
of  deposits  of  food  and  secretions  of  the  mouth,  which  are  likely  to  un- 
dergo chemical  change  by  long  confinement  in  contact  with  the  tissues, 
and  thus  become  irritants.  Either  one  or  all  of  the  conditions  named 
may  cause  inflammation  of  the  mucous  membrane,  but  always,  so  far  as 
the  author's  observation  has  gone,  limited  to  the  area  covered  by  the 
plate.  Similar  conditions  are  frequently  noticed  when  the  dentures  were 
of  gold  or  silver,  but  always  in  cases  where  the  plate  was  seldom  removed 
or  cleansed.  And  if  the  trouble  referred  to  is  more  common  in  rubber 
or  celluloid  dentures  than  where  metallic  plates  are  worn,  there  are 
doubtless  more  conditions  favoring  such  a  result  in  the  former  than  are 
found  in  the  latter ;  and  the  facts  that  the  symptoms  are  not  constant, 
and  that  by  far  the  greater  number  of  mouths  in  which  rubber  or  cellu- 
loid is  worn  are  not  in  the  least  aflFected  by  it,  would  seem  to  confirm  the 
view  that  the  inflammation  referred  to  is  due  to  contact  with  irritating 
products  of  food  and  secretions,  and  that  these  are  equally  active  in  all 
dentures,  irrespective  of  the  material  of  which  the  denture  are  made. 

Rubber  sore  mouth  as  described  in  the  American  System  of  Dentis- 
try, if  met  with  at  all,  must  be  exceedingly  rare,  and  the  "  rubber  sore 
mouth"  which  passes  the  stage  of  redness  and  slight  tenderness  and 
extends  to  the  tonsils  and  walls  of  the  pharynx,  with  the  parts  greatly 
swollen  and  painful,  rendering  the  wearing  of  the  plate  impossible  for 
the  time  and  the  formation  of  abscesses,  the  author  has  never  seen. 

Acute  inflammatory  conditions  of  the  mouth  which  appear  with  some 
degree  of  suddenness  may  often  be  traced  to  persistent  efforts  on  the 
part  of  the  patient  to  obtain  atmospheric  adhesion  in  a  badly-fitting 
denture  by  powerful  suction  of  the  tongue  in  the  effort  to  exhaust  the 
air  from  the  chamber  :  violence  of  this  kind,  aided  by  the  other  unfavor- 
able conditions  referred  to,  may  cause  occlusion  of  mucous  follicles  and 
the  usual  inflammation  resulting  from  interruption  of  the  secretions  ;  but 
it  would  be  manifestly  wrong  to  class  such  conditions  under  the  heading 
of  "  Rubber  Sore  Mouth." 

The  great  majority  of  cases  of  local  irritation  associated  with  the 
wearing  of  dentures  are  not  usually  cases  calling  for  the  exhibition  of 
drugs,  but  as  the  rules  of  hygiene  extend  to  all  conditions  which  may 
cause  departure  from  a  normal  standard  of  health,  whether  local  or 
general,  the  first  step  in  the  treatment  of  so-called  "  rubber  sore  mouth" 
should  be  an  examination  of  the  plate  to  determine — 1st,  if  there  is  accu- 
racy of  adaptation ;  2d,  is  the  surface  of  denture  smooth  enough,  and 
in  proper  condition  to  be  constantly  worn  in  contact  with  the  delicate 


EXCESSIVE  ABSORPTION.  707 

tissues  of  the  mouth  ?  3d,  is  the  denture  free  of  deposits  of  food  and 
secretions  ?  A  cure  will  usually  be  promptly  effected  by  the  fulfilment 
of  the  three  conditions  named. 

Rubber  dentures  favor  the  deposition  of  material  composed  of  food 
and  mucus  secreted  from  the  follicles  of  the  tissues  covered  by  the 
plate,  which  often  escapes  the  observation  of  the  patient  and  is  always 
difficult  to  remove  thoroughly.  The  patient  should  be  carefully  instructed 
as  to  the  best!  means  of  keeping  the  denture  free  from  this  deposit, 
which  will  consist  in  the  frequent  use  of  a  strong  solution  of  soda,  in 
which  the  plate  should  occasionally  remain  immersed  over  night,  and 
when  the  deposit  is  thoroughly  softened  by  the  soda  solution  the  careful 
use  of  the  tooth-brush  armed  with  soap  and  tooth-powder.  Salivary 
calculus,  which  often  deposits  in  large  quantities  on  lower  plates,  may 
be  removed  by  immersing  the  denture  over  night  in  vinegar  and  water ; 
but  if  crowns  of  natural  teeth  have  been  reset  on  metallic  plates,  the 
salivary  calculus  must  be  removed  by  instruments,  as  any  form  of  acid 
would  dissolve  the  enamel  and  ruin  the  teeth. 

If  a  chronic  state  of  inflammation  of  the  surface  covered  by  the  den- 
ture has  become  established  by  violation  of  the  conditions  essential  to 
maintenance  of  a  normal  state  of  the  oral  tissue,  local  applications  of 
phenol  sodique,  thymozone,  or  listerine,  diluted  in  the  proportion  of  one 
part  of  the  remedy  to  three  or  four  of  water,  will  generally  relieve  the 
tissues  of  redness  and  tenderness. 

In  cases  of  long  standing  and  unusual  severity  zinci  sulphas  in  solu- 
tion, in  the  strength  of  gr.  j  or  ij  to  f  ^ss  of  water,  will  be  found  of  great 
service  as  an  application  to  the  inflamed  parts. 

Some  authorities  state  that  chronic  stages  of  so-called  "  rubber  sore 
mouth "  are  curable  only  by  the  substitution  of  a  denture  made  upon 
metal.  Such  cases  the  author  has  never  met  with,  and  he  believes  that 
careful  fulfilment  of  the  conditions  of  precision  of  adaptation,  smooth- 
ness of  surface  in  contact  with  the  tissues,  and  absolute  cleanliness  will 
generally  be  found  sufficient  to  restore  the  mouth  to  a  normal  state. 

Excessive  absorption  of  the  alveolar  ridge,  ending  in  the  entire 
obliteration  of  any  semblance  of  a  ridge,  is  extremely  rare,  and  not  a 
single  instance  of  the  kind  has  been  met  with  by  the  author  in  his  entire 
practice.  The  few  cases  of  absorption  of  the  anterior  portion  of  the  ridge 
which  have  come  under  his  notice  have  been  mouths  in  which  metal 
plates  have  been  worn.  This  phenomenon  has  been  attributed  to  the 
poisonous  action  of  vermilion  used  in  dental  rubbers  as  a  pigment ;  im- 
perfect vulcanization,  causing  porosity  of  the  plate,  thus  favoring  the 
absorption  of  secretions  or  the  growth  of  micro-organisms  on  that  por- 
tion of  the  plate  in  contact  with  the  mucous  membrane  ;  but  it  is  quite 
probable  that  excessive  absorption  of  the  alveolar  ridge  is  an  inherited 
tendencv.  The  author  has  observed  that  condition  in  more  than  one 
member  of  the  same  family,  and  he  has  very  recently  made  dentures  for 
a  gentleman  of  advanced  age  and  his  daughter,  in  both  of  whose  mouths 
the  anterior  portion  of  the  alveolar  ridge  has  quite  disappeared,  while 
the  ridge  in  the  posterior  part  of  both  mouths  is  unusually  broad  and 
prominent. 

Pure  vermilion,  in  combination  with  rubber,  is  not  likely  to  produce 
deleterious  effects  when  worn  in  the  mouth,  nor  is  it  probable  that  this 


708  RELATIONS  AND  CARE  OF  ARTIFICIAL  DENTURES. 

compound  can  be  decomposed  chemically  and  converted  into  a  poisonous 
salt  of  mercury  by  mere  contact  with  the  saliva. 

The  mechanical  dentist  will,  however,  do  well  to  avoid  the  use  of 
nitrohydrochloric  acid  in  removing  tin-foil  from  the  surface  of  unfin- 
ished vulcanite  dentures.     (See  chapter  on  Metallurgy  :  Mercury.) 

Regarding  the  presence  of  free  mercury  in  rubber  before  or  after 
vulcanizing,  Prof.  Austin  stated  that  the  researches  of  Prof.  Johnston 
with  the  microscope,  and  of  Prof.  Mayer  by  chemical  analysis,  failed  to 
discover  the  slightest  trace  in  samples  of  that  which  had  been  used  for 
several  years.  Prof.  Wildman  observed  that  sulphur  sublimed  during 
vulcanization,  but  did  not  find  the  smallest  trace  of  free  mercury.  Prof. 
Austin  further  stated  that  he  never  during  his  entire  experience  with 
indurated  rubber  as  a  base  for  artificial  dentures  detected  the  slightest 
particle  of  metallic  mercury  on  the  surface  of  any  finished  jjiece. 

In  the  belief  that  mercuric  sulphide  (vermilion)  may  be  the  cause  of 
the  different  phases  of  so-called  rubber  sore  mouth,  the  substitution  of 
black  for  red  rubber  has  been  recommended  as  a  means  of  overcoming 
the  tendency  to  excessive  tenderness  of  the  mucous  membrane  covered 
by  the  plate.  Black  rubber  is  but  a  doubtful  improvement  upon  the 
red  variety  so  far  as  influence  on  the  health  of  the  tissues  is  concerned. 
As  it  contains  lampblack  as  a  pigment,  it  is  uncertain  whether  it  is 
more  den.se  and  less  liable  to  absorb  secretions.  The  best  quality  of 
rubber  for  dental  purposes,  the  one  affording  the  greater  density  of 
surface,  is  that  which  is  composed  simply  of  caoutchouc  48  parts,  sul- 
phur 24  parts,  without  any  pigment  whatever.  This  rubber  is  of  a 
dark  drab  color,  and  it  differs  so  widely  from  the  color  of  the  tissues 
that  it  has  never  been  employed  to  any  great  extent  in  prosthetic  den- 
tistry. 

Vulcanizable  rubbers,  of  whatever  composition,  require  great  care 
both  in  investing  and  indurating.  Campbell,  the  inventor  of  the  "  New 
Mode  Heater  for  Rubber  and  Celluloid  Work,"  demonstrated  that  the  only 
way  to  obtain  fine  texture  and  density  of  surface  in  rubber  and  celluloid 
is  to  expose  them  to  low  temperature,  dry  heat,  and  contact  with  metallic 
surfaces.^  This  produces  a  harder  rubber,  less  porous  and  less  liable 
to  absorb  the  secretions  than  can  be  obtained  by  contact  with  plaster,  or 
indeed  by  any  other  means ;  but  where  the  modus  operandi  suggested 
by  Drs.  Campbell  and  Evans  is  practised  the  preliminary  "waxing" 
of  the  case  must  be  done  with  such  precision  that  the  surface  thus 
obtained  need  not  be  subsequently  disturbed  by  the  scraper.  (See  chap- 
ter on  Vulcanite  and  Celluloid  Work.) 

The  theory  presented  by  Dr.  G.  V.  Black,  that  the  sore  mouth  pro- 
duced by  artificial  dentures  is  due  to  the  growth  of  certain  fungi  which 
elaborate  an  acid  secretion  which  acts  as  an  irritant  to  the  mucous  mem- 
brane, is  probably  correct.  He  asserted  that  he  found  these  fungi  upon 
the  surfaces  of  all  plates  without  regard  to  the  material  of  which  they 
were  constructed,  but  in  the  greatest  number  upon  the  surfaces  of  vul- 
canite dentures ;  which  he  attributed  to  the  fact  that  the  irregularities 
and  roughnesses  of  the  surfaces  of  such  plates  afforded  lodging-places 
where  they  rapidly  developed  on  account  of  the  greater  difficulty  in 

^  The  manufacturers  of  rubber  articles  of  jewelry  and  ornamentation  long  since  aban- 
doned the  use  of  steam  as  a  heating  medium  and  plaster  as  an  investment. 


PARTIAL  ARTIFICIAL  DENTURES.  709 

thoroughly  cleansing  them,  and  he  regards  absolute  cleanliness  as  a 
complete  protection  from    inflammation. 

Prof.  E.  C.  Kirk  stated,  as  the  result  of  repeated  tests  of  the  mucous 
secretion  in  cases  of  sore  mouth  associated  with  the  rubber  denture,  that 
the  mucus  in  such  cases  generally  showed  an  alkaline  reaction  as  it  was 
eliminated ;  and  he  suggests  the  possibility  that  alkaline  sulphides 
might  be  eliminated  to  a  sufficient  extent  to  exert  a  slight  solvent  action 
upon  the  mercuric  sulphide  of  the  plate,  and  thus  form  an  active  salt 
of  mercury.  But  this  theory  seems  to  be  at  variance  with  the  more 
practical  reasoning  and  experience  of  many  others  who  have  given  much 
thought  and  attention  to  the  subject.  Prof.  Kirk's  suggestion,  how- 
ever, that  the  non-conducting  quality  of  the  vegetable  bases  plays  an 
important  part  in  the  production  of  every  kind  of  inflammatory  action 
undoubtedly  carries  with  it  much  force,  for,  as  he  states,  "the  effect  on 
the  tissues  continually  enclosed  by  the  non-conducting  plate  is  to  main- 
tain a  hypersemic  condition,  with  slight  increase  of  temperature  :  this  in 
addition  to  the  pressure,  which,  if  it  does  not  result  in  inflammation,  is 
a  source  of  irritation  sufficient  to  bring  about  greatly  increased  func- 
tional activity  of  the  cells  of  the  parts." 

It  was  at  one  time  thought,  and  so  claimed  by  many  of  its  advocates, 
that  the  substitution  of  celluloid  for  rubber  dentures  would  prove  an 
effective  remedy  in  cases  of  sore  mouth  ;  but  that  material  is  open  to  the 
same  objections  as  rubber,  and  to  a  greater  degree  in  consequence  of  the 
sponginess  of  surface  incident  to  the  evaporation  of  camphor. 

Partial  artificial  dentures  immovably  attached  to  one  or  more  natural 
teeth  or  roots  of  teeth,  or  the  attachment  of  several  crowns  to  one  or 
more  roots  as  in  bridge-work,  present  many  points  for  consideration 
from  a  hygienic  standpoint.  The  operation  of  substituting  an  artificial 
crown  for  a  natural  one  should  not,  if  properly  performed,  affect  the 
integrity  of  any  of  the  surrounding  tissues,  and  yet  if  the  work  is  ill- 
fitting  and  done  in  a  slovenly  manner,  with  the  cap  or  ferrule  extend- 
ing so  far  under  the  free  margin  of  the  gum  as  to  impinge  upon  the 
alveolar  border  of  the  socket,  persistent  irritation  may  be  established, 
which  can  only  end  in  disorganization  of  connective  tissue  and  loss  of 
the  root  if  the  cause  be  not  removed.  The  experience  of  the  author 
has  been  that  roots  upon  which  artificial  crowns  have  been  fixed  are  less 
liable  to  pericemental  inflammation  and  abscess  than  are  devitalized  teeth 
with  natural  crowns,  the  greater  success  in  the  treatment  of  the  crownless 
root  being  probably  due  to  its  accessibility  and  the  better  opportunity 
which  undoubtedly  exists  of  filling  the  latter  with  thoroughness  to  the 
full  extent  of  the  canal. 

The  fact,  too,  of  restoring  occlusion,  whereby  roots  are  brought  into 
use,  helps  to  keep  them  in  a  healthy  condition,  and  prevents  their 
gradual  extrusion  and  premature  loss  from  the  alveoli. 

As  is  well  known,  there  are  a  variety  of  methods  of  setting  artificial 
crowns  to  roots.  Any  one  of  these  methods,  if  lacking  in  the  ele- 
ment of  precision  of  adjustment,  may  favor  the  establishment  of  patho- 
logical conditions.  The  Richmond  crown,  properly  so  called,  with  an 
accurately  fitted  cup  or  ferrule,  is  perhaps  less  liable  to  cause  irritation  to 
the  surrounding  tissues  than  any  of  the  methods  of  crown-setting  in  use. 

The  worst  results  have  been"  noticed  in  that  class  of  crowns,  without 


710  RELATIONS  AND  CARE  OF  ARTIFICIAL  DENTURES. 

caps  or  ferrules,  in  which  the  attachment  to  the  root  is  secured  by  means 
of  amalgam.  If  the  latter  is  allowed  to  project  at  the  point  of  union 
of  the  crown  and  root,  it  soon  becomes  exceedingly  irritating  to  the  mar- 
gins of  the  gum — a  condition  marked  by  redness,  tumefaction,  and  a 
tendency  to  bleed,  particularly  in  the  recumbent  position  at  night,  and  a 
nocturnal  flow  of  saliva  similar  to  that  noticed  in  pyorrhoea  alveolaris 
becomes  established.  The  only  remedy  for  chronic  dental  irritation  due 
to  this  cause  is  the  removal  of  the  crowns  and  the  substitution  of  others 
which  are  not  dependent  upon  amalgam  as  a  means  of  attachment. 

Bridge-"Work,  which  consists  of  the  bridging  of  interdental  spaces  by 
one  or  more  crowns  fastened  together  and  attached  to  natural  teeth  or 
roots,  frequently  causes  pathological  conditions  from  a  want  of  care  and 
exactness  in  their  construction,  and  by  requiring  two  or  more  roots  to  sus- 
tain an  amount  of  force  in  mastication  greatly  in  excess  of  that  for  which 
they  were  intended.  As  a  result  of  the  excessive  strain  to  which  they 
are  subjected  under  such  conditions,  fracture  of  the  roots,  chronic  in- 
flammation of  their  pericemental  membranes,  abscesses,  or  protracted 
tenderness  may  occur,  either  of  these  being  sufficient  to  seriously  inter- 
fere with  mastication  and  render  the  denture  useless. 

Cases  of  serious  local  irritation  from  unusual  causes  are  occasionally 
met  with  in  so-called  bridge-work.  The  author  recently  met  with  a  case 
in  which  a  bridge  had  been  constructed  for  the  purpose  of  replacing  two 
right  superior  bicuspids.  The  attachment  consisted  of  a  wire  of  ordinary 
18-carat  gold  fastened  with  amalgam  in  the  cuspid  and  first  molar,  both 
of  which  were  devitalized.  The  wire  had  gradually  yielded  under  the 
pressure  of  mastication  until  the  necks  of  the  two  artificial  teeth  had 
become  imbedded  in  the  gum  tissues,  which  were  so  much  swollen  that 
only  the  points  of  the  porcelain  teeth  were  visible.  The  general  health 
of  the  patient  was  greatly  affected  by  the  persistent  irritation  caused  by 
the  displaced  bridge  :  no  time  was  therefore  lost  in  removing  it.  This 
was  done  with  the  greatest  relief  to  the  patient,  the  tissues  returning 
within  a  few  days  to  their  normal  condition. 

Although  skilful  and  experienced  bridge-workers  generally  plan  and 
construct  dentures  of  this  class  with  special  reference  to  complete  clean- 
liness, yet  it  is  doubtful  whether  all  parts  of  the  best  of  them  can  be 
reached  by  the  tooth-brush  as  thoroughly  as  is  the  case  with  the  ordinary 
removable  denture.  In  many  cases  the  irritation  induced  by  the  impac- 
tion of  food-debris  and  fermenting  secretions,  and  the  unusual  strain 
upon  roots  of  diseased  teeth,  will  cause  hypertrophy  of  the  surrounding 
tissues  or  rapid  loosening  from  absorption  of  their  alveolar  borders. 
These  conditions  are  always  accompanied  by  more  or  less  vitiation  of 
the  secretions  of  the  mouth  and  foulness  of  breath,  constituting  in  many 
cases  potent  arguments  against  their  introduction. 

Of  the  different  methods  of  constructing  this  class  of  dentures,  the 
removable  bridge  introduced  and  described  by  Dr.  C.  M.  Richmond  is 
probably  open  to  fewer  objections  than  any  of  the  other  forms ;  yet  even 
that  plan  requires  good  judgment  in  determining  the  capability  of  teeth 
or  roots  to  sustain  the  extraordinary  strain  to  which  they  must  neces- 
sarily be  subjected,  and  the  greatest  skill  and  care  in  the  construction 
and  adjustment  of  the  different  parts  of  the  fixture. 

The  introduction  of  immovable  "  bridge  "  dentures  has  undoubtedly 


IMPORTANCE  OF  CLEANLINESS.  711 

in  a  great  many  cases  caused  so  much  discomfort  and  irritation  to  sur- 
rounding tissues  as  to  render  mastication  almost  impossible,  and  it  is 
doubtful  whether  extensive  operations  of  this  class,  considered  from 
their  hygienic  relations,  are  as  satisfactory  as  properly  planned  and 
constructed  removable  dentures  retained  in  position  by  atmospheric 
adhesion. 

Care  in  cleansing  artificial  dentures  of  whatever  form,  size,  or  material 
is  of  the  utmost  importance.  The  cleansing  should  be  performed  imme- 
diately after  eating,  and  particularly  before  retiring  for  the  night.  If 
this  be  not  done  with  some  degree  of  thoroughness,  debris  of  food  mixed 
with  saliva  and  mucus  forms  an  adherent  mass  upon  the  plate  which 
undergoes  fermentation  and  decomposition,  with  the  result  of  irritating 
the  mucous  membrane  and  producing  a  general  inflammation  of  the  oral 
cavity,  and  the  irritation  of  the  oral  secretions  may  cause  serious  de- 
rangement of  the  digestive  function. 

It  is  the  duty  of  the  dentist  to  instruct  his  patient  as  to  the  import- 
ance of  cleanliness  and  in  the  proper  means  by  which  that  result  may  be 
accomplished.  The  thorough  cleansing  of  an  artificial  denture,  although 
apparently  a  simple  operation,  seems  to  be  a  matter  of  great  difficulty  to 
the  majority  of  patients,  and  but  few  are  capable  of  maintaining  a  fault- 
less condition  of  their  dentures ;  yet  the  tooth-brush  armed  with  soap 
and  ordinary  tooth-powder  is  quite  sufficient  to  maintain  a  clean  and 
highly  polished  surface.  The  patient  should  be  cautioned  against  the 
danger  of  bending  partial  lower  dentures  of  gold  or  other  metals  by 
grasping  them  with  too  much  force  while  brushing,  and  in  the  case  of 
vulcanite  dentures  to  avoid  "  boiling  them  out "  in  hot  water.  Many 
individuals  who  have  previously  worn  gold  dentures  resort  to  that 
means  of  ridding  the  fixture  of  deposits  of  food,  etc.  which  have  found  a 
lodgement  under  the  teeth  and  behind  the  backing.  The  author  has 
met  with  several  instances  where  recently  constructed  vulcanite  dentures 
have  been  completely  ruined  within  a  short  time  of  their  completion  by 
immersion  in  boiling  water. 

In  the  construction  of  metallic  plates  for  partial  dentures  the  plate 
should  be  accurately  fitted  around  remaining  natural  teeth,  so  that  there 
will  be  no  spaces  between  the  plate  and  the  teeth  to  admit  of  pinching  of 
the  gum  between  the  edge  of  the  former  and  the  neck  of  the  tooth ;  and 
where  a  point  of  the  plate  extends  betAveen  two  teeth — as,  for  instance, 
the  central  incisors — such  projection  must  be  made  to  fit  the  space  accu- 
rately, or  it  will  be  certain  to  cause  inflammation  which  may  result  in 
permanent  impairment  of  the  teeth.  Defects  of  this  kind  may  be  cor- 
rected by  soldering  an  addition  to  the  edge  of  the  plate  in  order  to  bring 
it  almost  in  contact  with  the  teeth,  or  else  by  cutting  away  the  plate  so 
freely  that  its  distance  from  the  teeth  will  preclude  the  danger  of  pinch- 
ing the  tissues. 


CHAPTER    XXI. 

PALATAL  MECHANISM. 

By  Rodeigues  Ottolengui,  M.  D.  S.^ 


Cleft  Palate. 


Cleft  palate  may  be  divided  into  two  classes  —  acquired  and  con- 
genital. Acquired  lesions  include  all  of  those  cases  where  the  indi- 
vidual, having  been  born  with  a  normal  oral  cavity,  later  in  life  suffers 


Fig.  957. 


a  division  of  the  hard,  or  of  the  soft  palate,  or  of  both.  This  unfortu- 
nate mischance  may  be  caused  by  an  accident,  such  as  a  knife-thrust ; 
the  sequence  of  disease,  usually  syphilis  ;  or  the  result  of  a  surgical  opera- 
tion for  the  removal  of  malignant  growths. 

^  I  am  indebted  to  Dr.  Norman  W.  Kingsley  for  the  use  of  his  large  collection  of 
models  from  which  to  choose  for  illustrations,  as  well  as  for  the  privilege  of  referring  to 
cases  from  his  practice  in  order  to  more  clearly  expound  the  theories  and  principles  set 


forth 

712 


CLEFT  PALATE. 


713 


Tlie  acquired  lesions  may  be  very  slight,  as  a  mere  perforation  of  the 
hard  palate,  or  they  may  be  most  extensive  in  character,  comprising  a 
complete  cleft  of  the  hard  and  soft  palate,  with  total  destruction  of  the 
vomer  and  turbinated  bones,  as  well  as  the  bridge  of  the  nose,  and 
sometimes  the  nose  itself.  Such  an  extreme  case,  of  course,  would  only 
have  its  origin  in  disease.  Between  the  two  extremes  cited  an  endless 
variety  of  cases  are  found,  many  of  which  will  tax  the  ingenuity  of  the 
operator  to  its  utmost.  The  conditions  which  may  follow  upon  unsuc- 
cessful^ surgical  operations  frequently  add  to  the  complexities  of  cases. 
Fig.  957  shows  such  a  case,  the  absence  of  the  uvulse,  and  the  adhesions 
which  have  united  the  posterior  borders  of  the  divided  soft  palate  to 
the  pharyngeal  wall,  making  this  case  readily  distinguishable  from  one 
of  congenital  origin. 

Nevertheless,  whether  the  acquired  lesion  be  of  small  or  great  extent, 
the  prognosis  is  more  certain  than  in  the  congenital  cases,  because  it  has 
been  demonstrated  that  if  the  operator  succeeds  in  replacing  the  lost 
parts  with  an  instrument  properly  constructed  and  suited  to  the  indi- 
vidual requirements,  normal  functions  will  be  restored  almost  imme- 
diately.    The  patient  needs  but  to  accustom  himself  to  the  new  and 

Fig.  958. 


strange  condition  in  which  he  finds  himself,  to  be  able  to  speak  as  well 
as  ever ;  this  because  he  had  acquired  all  the  normal  habits  of  articu- 
late speech  before  meeting  with  disaster.  He  has  lost  part  of  the 
natural  organs  with  which  he  was  endowed,  but,  having  known  their 
uses,  he  readily  accustoms  himself  to  the  artificial  substitute,  which 
enables  him  to  produce  the  same  sounds  by  the  same  movements  of  the 
organs  which  remain  intact.     As  the  instruments  to  be  made  for  persons 


714 


PALATAL  MECHANISM. 


suifering  from  such  misfortune  are  to  be  constructed  on  the  same  general 
principles  which  must  guide  the  dentist  in  the  treatment  of  congenital 
lesions,  description  at  this  point  is  unnecessary. 

Congenital  cleft  palate  is  a  division  of  the  roof  of  the  mouth  of  more 
or  less  extent,  which  is  present  in  the  infant  at  the  time  of  birth. 

Congenital  clefts  come  to  the  dentist  for  treatment  in  one  of  three 
conditions :  The  cleft  of  the  soft  palate  only,  which  may  extend  to 
the  posterior  border  of  the  hard  palate  or  be  scarcely  more  than  the 
division  of  the  uvula,  as  in  Fig.  958  ;  the  cleft  of  the  soft  and  hard 
palate,  in  which  the  cleft  may  penetrate  the  bony  tissue  but  slightly  or 
pass  through  the  hard  palate  and  also  the  dental  process,  obliterating 
entirely  the  intermaxillary  bones,  as  in  Fig.  959  :  any  of  the  above  con- 

FiG.  959. 


ditions  complicated  in  an  endless  variety  of  ways  through  unsuccess- 
ful surgical  operations.  In  these  latter  cases  the  most  common  pre- 
sentment is  a  bridging  of  the  gap,  with  the  soft  tissues  drawn  together 
tensely,  leaving  an  aperture  through  the  hard  palate  anteriorly  and  an 
inadequate  length  of  soft  palate  posteriorly,  the  tightly  drawn  tissues 
which  form  the  surgical  bridge  not  being  long  enongh  to  occlude  with 
the  posterior  pharyngeal  wall ;  or  where  there  has  been  only  a  cleft  in 
the  soft  palate,  the  cleft  is  usually  found  partially  closed,  with  no 
advantage  to  the  patient,  and  offering  a  greater  obstacle  to  the  success 
of  the  dentist. 

In  some  of  these  cases  the  intervention  of  the  dentist  is  rendered 
useless,  while  in  those  where  it  is  possible  to  make  an  instrument,  the 


CLEFT  PALATE.  715 

difficulty  of  constructing  the  same  is  greatly  increased,  owing  to  the 
complexities  of  the  altered  conditions. 

The  modern  instrument  which  the  skilled  dentist  supplies  to  a  cleft- 
palate  patient,  is  either  an  artificial  velum  or  an  obturator,  both  of  which 
are  admirably  adapted  to  the  correction  of  the  abnormal  speech  of  these 
suiFerers,  and  either  of  which  may  be  requisite  in  a  special  case.  It  may 
be  stated,  however,  as  a  rule  for  guidance  in  general  practice,  that  the 
artificial  velum  will  more  quickly  enable  a  cleft-palate  patient  to  acquire 
the  aft  of  speaking  correctly,  whilst  after  having  learned  to  speak  prop- 
perly  the  obturator  may  afford  him  equal  satisfaction. 

The  above  statement  is  an  important  truth  which  should  be  promi- 
nently borne  in  mind ;  and,  moreover,  it  is  this  fact  which  accounts  for 
the  many  recorded  cases  where  dentists  have  replaced  artificial  vela 
with  obturators,  often  poorly  constructed,  and  then  have  hastily  pub- 
lished the  statement  that  the  patient  liked  his  instrument  so  much  better 
than_  the  other,  and  that  "  she  talked  perfectly  as  soon  as  my  obturator 
was  inserted."  In  making  obturators  for  persons  who  have  never  worn 
an  instrument  of  any  kind  tlieir  results  would  be  much  less  favorable. 

The  knowledge  of  how  best  to  serve  a  cleft-palate  patient,  and  what 
manner  of  instrument  is  best  adapted  to  his  requirements,  necessitates 
an  intelligent  comprehension  of  his  needs,  as  well  as  of  the  principles 
upon  which  obturators  and  vela  are  constructed,  together  with  the  uses 
which  they  are  meant  to  serve. 

In  the  production  of  articulate  sounds  the  normal  individual  is  sup- 
plied with  a  soft  palate,  or  natural  velum,  of  great  mobility,  suspended 
from  the  posterior  border  of  the  hard  palate.  This  natural  velum  serves 
two  important  purposes :  First,  it  is  needful,  in  the  production  of  many 
sounds,  that  they  should  be  free  from  nasal  resonance,  which  would  result 
if  permitted  to  escape  through  the  nasal  passages.  That  the  nasal  and 
oral  cavities  may  be  completely  separated,  the  posterior  wall  of  the 
pharynx  rises,  forming  a  well-defined  ridge,  against  which  the  vehnn 
occludes,  being  drawn  backward  and  upward  to  meet  it.  Thus  the 
sound  is  forced  to  pass  exclusively  through  the  mouth,  and  is  rendered 
clear  and  distinct.  Second,  the  natural  soft  palate  serves  as  an  abut- 
ment against  which  the  tongue  rises  in  the  formation  of  such  sounds  as 
Ic,  g,  and  ng. 

A  cleft  of  the  palate  consequently  leaves  the  patient  with  no  means 
of  shutting  off  the  nasal  passages,  and  with  an  inadequate  organ  with 
which  to  produce  the  sounds  specified  as  well  as  many  others. 

The  artificial  palate,  therefore,  whether  velum  or  obturator,  must 
enable  the  patient  to  completely  shut  off  the  nasal  passages,  and  it 
must  stop  the  gap  in  the  roof  of  the  mouth,  restoring  the  normal  vault, 
and  rendering  possible  the  production  of  all  the  sounds  with  which  the 
cleft  interfered.  The  artificial  velum  and  the  obturator  both  accomplish 
this,  but  their  modes  of  action  are  quite  distinct. 

The  artificial  velum  which  has  proven  to  be  the  simplest  and  at  the 
same  time  the  most  universally  efficacious  is  the  invention  of  Dr.  Xorman 
W.  Kingsley.  It  is  made  of  soft  rubber  (vulcanite),  from  which  fact  it 
is  clear  that  the  theory  of  its  action  is  to  simulate  the  movement  of  the 
natural  organ  which  it  replaces.  Being  exceedingly  mobile,  it  responds 
to  the  movements  of  the  muscles  which  it  engages,  rising  and  falling 


716 


PALATAL  MECHANISM. 


exactly  as  a  natural  velum  would,  while  it  is  so  fashioned  that  at  the 
same  time  it  occludes  with  the  ridge  of  the  pharyngeal  wall,  completely 
shutting  off  the  upper  passages. 

The  Kingsley  velum   (Figs.  960-962)  consists  of  two  flaps  joined 
throughout  the  median  line.     The  lower  flap,  the  one  which  completes 


Fig.  960. 


Fig.  961. 


Fig.  962. 


the  palatal  dome,  extends  from  the  apex  of  the  fissure  posteriorly  as  far 
as  the  bases  of  the  uvulse.  Its  general  form  is  that  of  a  triangle,  the 
apex  of  which  occludes  with  the  apex  of  the  cleft,  the  base  extending 
across  from  one  uvula  to  the  other.  This  flap  overlaps  the  soft  parts 
sufiiciently  to  prevent  its  being  pushed  through  the  cleft  into  the  upper 
cavity.  The  other  flap  is  of  a  similar  triangular  shape,  the  posterior 
border,  however,  being  curved  and  thinned  out  to  a  feather  edge,  so  that 
when  in  occlusion  with  the  pharyngeal  wall  it  curls  up,  thus  presenting 
a  flat  surface  for  better  contact,  while  its  thinness  prevents  irritation  to 
these  sensitive  parts.  This  flap  is  above  the  fissure  and  rests  upon  the 
upper  surfaces  of  the  divided  palate.  The  two  flaps  are  united  along 
the  median  line,  so  that  when  complete  they  form  a  single  appliance. 
The  flaps  having  but  a  narrow  line  of  union,  grooves  are  produced 
laterally,  and  when  in  position  the  two  halves  of  the  soft  palate  rest 
in  these  grooves. 

In  connection  with  the  artificial  velum  a  metal  plate  is  constructed, 
clasped  to  the  teeth,  having  a  pin  upon  the  upper  surface  which  passes 


CLEFT  PALATE. 


Ill 


through  a  hole  in  the  velum,  and  thus  holds  it  in  place  while  allowing 
it  lateral  motion.  Fig.  963  shows  an  instrument  in  position,  the  uvulse 
appearing  pendant  below  the  grooves  of  the  artificial  palate.  Note  the 
relation  between  the  posterior  border  of  the  velum  and  the  wall  of  the 


Fig.  963. 


pharynx.  The  rationale  of  this  appliance  is  as  follows :  In  the  effort 
to  close  off  the  upper  passages  the  sides  of  the  divided  natural  palate 
approximate  each  other,  and  at  the  same  time  are  drawn  upward.  Thus 
they  first  hug  the  artificial  velum  tightly,  and  then,  owing  to  its  elas- 
ticity, carry  it  upward.  Coincidently,  the  wall  of  the  pharynx  rises, 
forming  a  ridge  which  meets  the  feather  edge  of  the  artificial  velum, 

Fig.  964. 


curling  it  up,  thus  accomplishing  perfect  contact,  completely  preventing 
the  escape  of  sounds  through  the  nasal  passages.  At  the  same  time  the 
velum,  completing  the  proper  arch  of  the  vault,  is  rigid  enough  to  serve 
as  an  efficient  abutment  for  the  tongue  when  necessity  compels  such  con- 


718 


PALATAL  MECHANISM. 


tact.  Fig,  908  shows  the  upper  view  of  the  instrument  seen  in  Fig.  963, 
and  is  introduced  to  give  a  clearer  idea  of  the  attachment  of  the  vehim 
to  the  plate,  as  well  as  the  general  character  of  the  grooves. 

As  stated  above,  the  flaps  which  constitute  the  velum  are  triangular 
in  shape,  yet  it  will  be  observed  that  the  velum  shown  in  Fig.  962  is 
square  at  the  anterior  end.  Where  the  cleft  is  in  the  soft  palate  only 
the  triangular  velum  is  required,  but  where  the  cleft  passes  forward, 
entering  the  hard  palate,  it  is  frequently  more  desirable  to  fill  the  aper- 
ture in  the  hard  palate  by  vulcanizing  hard  rubber  upon  the  upper  side 
of  the  metal  plate,  the  soft-rubber  velum  having  a  square  end  to  meet  a 
similar  surface  of  the  hard  rubber. 

Such  an  instrument  is  seen  in  Fig.  965,  the  abutment  of  the  hard  and 
soft  rubber  being  clearly  indicated.     The  projecting  point  seen  in  this 

Fig.  965. 


figure  was  for  a  special  purpose,  and  is  not  ordinarily  required.  This 
patient  was  a  girl  aged  fourteen,  and  presented  an  extensive  fissure 
through  hard  and  soft  palate,  complicated  with  a  hare-lip,  upon  which 
a  fairly  good  result  had  been  obtained  by  a  surgical  operation  in  early 
life.  Fig.  966  shows  a  model  of  her  mouth,  the  aperture  seen  above  the 
incisors  representing  the  passage  of  the  fissure  through  to  the  nose,  but 
somewhat  exaggerated,  having  been  enlarged  with  a  knife  for  convenience 
in  constructing  the  instrument.  The  girl's  articulation  was  bad,  but  the 
greatest  difficulty  of  understanding  her  arose  from  the  excessive  nasal 
quality  of  her  voice.  Externally,  she  was  much  disfigured  by  the  fact 
that  the  ala  of  the  nose,  on  the  side  where  the  hare-lip  had  been,  was 
more  sunken  than  is  usual — so  much  so,  indeed,  that  the  nostril  on  that 
side  was  completely  closed.  If  the  reader  will  read  aloud  a  few  lines 
on  this  page,  and  while  doing  so  will  close  one  nostril  by  pressing  down 
the  ala  with  one  finger,  he  will  readily  discover  that  such  closure  of  the 
nostril  produces  considerable  nasal  quality  of  voice.  Thus  it  was  very 
desirable,  both  from  a  cosmetic  standpoint  and  for  the  benefit  of  her 
speech,  that  the  sunken  ala  should  be  raised.  Indeed,  the  father  of  the 
child  earnestly  solicited  an  attempt  of  this  nature.  Thereupon  the  writer 
adopted  what  proved  to  be  a  simple  and  effectual  method  of  accomplish- 


CLEFT  PALATE. 


719 


ing  the  desired  end.  The  metal  plate  having  been  fitted,  a  square  platinum 
bar  was  soldered  to  the  upper  side  and  bent  so  that  it  protruded  through 
the  nostril,  when  it  was  cut  off  short  enough  to  be  out  of  sight.  The 
hard  rubber  intended  to  plug  the  aperture  in  the  hard  palate  was  then 


Fig.  966. 


""""UHjliiBgi)" 


attached,  and  with  the  soft-rubber  velum  in  position  the  result  is  seen 
in  Fig.  965,  the  end  of  the  platinum  bar  being  shown  at  a.  The  next 
step  was  to  make  a  square  tube  which  should  telescope  over  the  platinum 
bar,  fitting  accurately,  so  that  motion  would  be  prevented.  To  the  end 
of  this  tube  was  soldered  a  platinum  button,  so  placed  that  when  in 
position  it  rested  against  the  inner  surface  of  the  sunken  ala  and  lifted 
it  to  a  proper  position.  Two  views  of  this  tube  and  button  attachment 
are  shown  (Fig.  965,  b  and  c).  In  use  the  instrument  is  placed  in  the 
mouth,  the  platinum  bar  passing  readily  into  the  nostril ;  then  the  but- 
ton attachment  is  slipped  over  the  bar  through  the  external  orifice  of 
the  nose,  the  ala  being  thus  distended,  and  at  the  same  time  exerting 
sufficient  pressure  to  prevent  its  dislodgement.  The  fixture  is  worn 
with  comfort,  and  the  button  attachment  is  tolerated  by  the  nose,  the 
pressure  not  being  sufficient  to  produce  ulceration  or  absorption.  More- 
over, while  the  child's  speech,  of  course,  was  not  immediately  improved 
by  the  introduction  of  the  palate  instrument,  the  nasal  resonance  was 
very  markedly  lessened  instantly  by  the  lifting  of  the  ala.  Consequently, 
it  will  be  but  a  question  of  time  when  her  speech  will  be  rendered 
normal,  which  it  never  would  have  been  with  one  nostril  closed. 

It  may  be  well  to  emphasize  the  fact  that  the  mere  insertion  of  an 
artificial  palate  cannot  be  expected  to  enable  the  patient  to  speak  cor- 
rectly, any  more  than  the  possession  of  a  piano  or  violin  would  make  the 


720  PALATAL  MECHANISM. 

owner  an  accomplished  musician.  The  artificial  palate,  properly  con- 
structed, supplies  the  patient  with  the  means  of  perfecting  his  speech, 
but  perfection  itself  must  come  through  practice.  Education  by  a 
teacher  who  thoroughly  comprehends  the  needs  of  the  cleft-palate  patient 
will  greatly  shorten  the  time  required  for  improvement,  as  well  as  ensure 
a  better  final  result.  But  the  co-operation  of  the  patient  is  a  requisite 
which  is,  strangely  enough,  not  always  to  be  counted  upon.  And  it  is 
those  persons  who  have  no  ambition  to  help  themselves,  who  have  claimed 
that  artificial  palates  have  done  nothing  for  them.  An  instance  of  this 
is  noted  in  a  young  man  at  college  and  approaching  manhood  who  seems 
to  have  no  conception  of  the  wretched  sound  of  his  speech.  An  instru- 
ment admirably  adapted  to  his  needs,  and  one  which  undoubtedly  made 
it  possible  for  him  to  attain  perfect  speech,  was  worn  by  him  but  three 
months,  and  then  discarded  as  of  no  value  to  him. 

One  reason  why  the  artificial  palate  cannot  be  expected  to  enable  the 
patient  to  speak  properly  at  once  is  this  :  With  normal  organs  one  pro- 
duces articulate  sounds  by  utilizing  the  normal  actions  of  his  throat- 
muscles  and  the  tongue  and  lips.  With  abnormal  organs,  as  with  a  cleft 
palate  and  hare-lip,  the  individual,  in  the  effort  to  produce  the  sounds 
which  he  hears  from  others,  compels  his  tongue,  lips,  and  throat-muscles 
to  adopt  habits  which  are  totally  dissimilar  to  normal  movements.  When, 
therefore,  the  artificial  palate  is  inserted,  with  which  perfect  speech  can 
be  attained  only  by  normal  movements,  it  is  evident  that  the  incorrect 
habits  must  first  be  overcome ;  and,  secondly,  the  correct  action  of  the 
organs  must  be  acquired.  Consequently,  those  dentists  Avho  report  that 
instruments  of  their  devising  correct  the  patients'  defective  speech  in- 
stantly, simply  report  what  is  not,  and  cannot  be  true  if  the  case  be  a 
congenital  one. 

Since  the  acquirement  of  wrong  modes  of  speech  must  prove  so  deter- 
ring to  the  patient  who  essays  to  improve  his  speech  by  resorting  to  an 
artificial  palate,  it  is  a  reasonable  corollary  that  the  earlier  the  instru- 
ment is  made  the  less  will  the  patient  have  to  overcome.  It  is  therefore 
both  wise  and  feasible  to  insert  appliances  even  before  the  appearance  of 
the  permanent  teeth.  The  co-operation  of  the  patient,  however,  being 
of  such  importance,  especially  where  lessons  in  articulation  are  to  be 
given — which  is  always  desirable — it  is  scarcely  wise  to  undertake  a  case 
until  the  little  patient  is  old  enough  to  appreciate  the  conditions  and 
their  remedy.  Therefore,  except  in  rare  cases  where  the  child  is  un- 
usually well  developed  and  mentally  bright,  it  is  best  to  wait  until  the 
fifth  or  sixth  year. 

This  statement  is  introduced  at  this  point  because,  whatever  doubt 
there  may  be  in  older  patients  as  to  the  choice  between  the  soft  velum 
and  the  obturator,  with  children,  and  especially  young  children,  the  velum 
is  the  one  and  only  best  dependence. 

An  obturator  is  an  instrument  designed  to  merely  fill  a  gap  or  close 
an  opening  in  the  palate.  To  be  of  any  service  the  instrument  must  be 
so  constructed  that  it  accomplishes  all  that  the  artificial  velum  enables 
the  patient  to  do,  even  though  in  an  entirely  different  manner.  It  must 
accurately  fill  the  cleft  when  the  parts  are  at  rest;  it  must  also  fill  the 
fissure  whenever  and  no  matter  how  far  the  movable  sides  of  the  cleft  are 
draron  upward.    To  serve  such  a  purpose  the  obturator  must  be  so  thick 


CLEFT  PALATE. 


721 


that  when  the  sides  of  the  palate  are  drawn  upward  to  their  greatest 
limit  they  still  rest  against  the  sides  of  the  obturator.  Moreover  it 
must  be  of  sufficient  length  to  be  reached  by  the  posterior  wall  of  the 
pharynx,  and  it  must  be  thick  enough  at  the  back  end,  so  that  when  the 
pharynx  does  come  into  contact  with  it  the  closure  of  the  posterior  nares 
will  be  complete.  When  using  the  term  '•  thick,"  allusion  is  made  to  the 
diameter  through  the  obturator  from  the  oral  to  the  nasal  surface,  not  to 
the  thickness  of  the  rubber,  for  these  obturators  are  hollow  bulbs  and 
the  rubber  has  but  the  thickness  of  a  single  sheet. 

In  Fig.  967  is  shown  a  model  with  an  obturator  in  position.     The 

Fig.  967. 


plate  is  made  of  iridio-platinum  and  the  obturator  is  a  hollow  bulb  of 
hard  rubber.  This  figure  shows  the  length  of  the  obturator  in  relation 
to  the  uvulse,  as  well  as  the  manner  in  which  the  oral  surface  of  the 
instrument  fills  the  gap  and  completes  the  arch  of  the  vault.  In  Fig. 
968  the  same  instrument  is  shown  in  profile.     It  is  seen  that  the  rubber 

Fig.  968. 


bulb  is  attached  to  the  metal  plate  by  passing  over  a  bar  which  is  sol- 
dered to  the  plate,  a  nut  holding  it  fast.  Thus  the  bulb  may  be  removed 
in  order  to  repair  or  alter  clasps  or  to  do  anything  requiring  the  ope- 
ration of  soldering,  which  would  be  difficult  to  properly  perform  were 
the  rubber  bulb  permanently  attached.    The  figure  also  shows  the  thick- 

46 


722  PALATAL  MECHANISM. 

ness  of  the  obturator,  which  is  so  shaped  that  as  the  divided  palate  rises 
contact  is  preserved.  This  instrument  is  a  modification  of  the  original 
Suersen  device. 

In  use,  an  obturator  of  this  kind,  unlike  the  artificial  velum,  is  sta- 
tionary in  its  position,  but  it  is  of  such  form  that  the  pharyngeal  muscles 
of  the  throat  in  the  movements  incidental  to  the  production  of  articulate 
sounds  hug  the  obturator,  and  so  separate  the  cavity  of  the  nose  from 
the  cavity  of  the  mouth. 

In  the  American  System  of  Dentistry  (vol.  ii.  p.  1068)  there  is  figured 
a  Suersen  obturator,  modified  by  the  addition  of  a  hinge,  for  which  the 
following  claim  is  made  :  "  The  main  advantages  of  this  appliance  are — 
that  it  is  made  of  a  durable  material,  is  easily  constructed,  and  that 
articulation  can  be  learned  vnth  it  more  readily  than  ivith  any  other  appli- 
ance.''^ This  claim  appears  to  be  based  upon  the  operation  of  the  hinge 
which  unites  the  obturator  with  the  plate,  but  this  is  a  misleading 
device.  To  the  inexperienced  it  might  appear  to  be  an  improvement, 
but  in  actual  practice  it  will  be  found  to  possess  no  advantage  over  the 
Suersen  obturator  without  the  hinge. 

Fig.  969. 


That  the  reader  may  better  comprehend  the  explanation  of  this  fact, 
illustrations  of  a  hinged  obturator  have  been  inserted.  Fig.  969  gives 
a  view  from  the  oral  aspect,  while  Fig.  970  shows  the  upper  side.  In 
both  figures  A  represents  the  metal  plate,  B  the  hinge,  and  C  the 
rubber  bulb  or  obturator. 

Unlike  the  artificial  velum,  the  obturator  may  be  immovable  and  yet 
subserve  its  purpose,  because  the  soft  parts  throughout  all  their  varied 
motions  are  always  in  contact  with  the  instrument,  the  utterance  of 
articulate  sounds  being  thus  rendered  possible.  The  addition  of  the 
hinge  is  intended  to  allow  the  lifting  of  the  obturator.  Even  granting 
that  the  levator  muscles  would  be  powerful  enough  to  accomplish  this, 
the  question  arises.  What  will  be  gained?  Unfortunately,  nothing, 
because  the  same  benefits  will  obtain  with  an  instrument  of  exactly  the 


CLEFT  PALATE.  723 

same  shape,  immovably  attached.      But  when  further  examination  of 
this  sort  of  appliance  is  made  in  the  mouth,  it  is  readily  seen  that  the 

Fig.  970. 


levator  wuseles  do  not  lift  the  hinged  obturator,  hut,  on  the  contrary,  they 
raise  the  sides  of  the  cleft,  which  slide  along  the  bidb  exactly  as  though  it 
were  immovable. 

The  original  of  the  instrument  shown  in  Figs.  969  and  970  was 
made  for  a  patient  who  for  years  had  been  wearing  a  soft-rubber  velum, 
with  which  he  had  learned  to  speak  correctly.  This  hinged  obturator 
did  not  rise  and  fall  as  it  was  expected  to  do,  and  the  patient  discarded 
it  and  reverted  to  the  velum.  Nevertheless,  with  the  hinged  instrument 
this  patient  talked  very  well,  the  reason  being  that,  having  learned  to 
speak  with  his  velum,  he  could  speak  with  the  obturator,  and  this  in  spite 
of  the  failure  of  the  hinge  action. 

One  of  these  appliances  was  made  for  a  young  lady  who  was  assured 
that  she  would  speak  well  within  a  year,  but  at  the  end  of  three  years 
no  improvement  was  noticed.  An  examination  of  the  appliance  in  the 
mouth  showed  that  the  levator  muscles  did  not  lift  the  bulb  at  all,  and 
it  was  more  of  an  embarrassment  than  an  advantage.  Unlike  the  pre- 
vious case,  where  the  patient  had  learned  to  speak  with  a  soft  velum, 
this  hinged  instrument  was  the  initial  effort  made  for  her  relief.  Again 
the  hinge  failed,  and  the  obturator  was  practically  the  same  as  one  con- 
structed without  a  hinge.  But  this  patient  found  her  appliance  of  no 
benefit  to  her,  whereas  when  she  was  given  the  same  plate  with  the  same 
hinge,  but  with  a  soft-rubber  velum  attached  to  it,  a  course  of  instruction 
covering  a  few  weeks  enabled  her  to  speak  quite  well,  and  she  will 
unquestionably  continue  to  improve  until  her  speech  is  perfect. 

These  two  cases  emphasize  the  fact,  which  should  be  prominently 
borne  in  mind,  that  the  soft-rubber  velum  is  the  instrument  best  adapted 
for  correcting  the  speech  of  cleft-palate  patients  :  that  having  learned  to 
speak  by  using  a  soft-rubber  velum,  these  persons  will  do  well  with  a 
Suersen  obturator,  with  a  hinged  obturator  whether  the  hinge  works 
or  not,  and  in  some  cases  even  with  the  crude  class  of  instruments 
designed  for  no  other  purpose  than  to  stop  the  opening  in  the  hard 
palate. 

There  is  but  one  possible  condition  where  a  hinge  is  needed  in  con- 
nection with  a  hard-rubber  bulb,  and  that  is  where  a  surgical  operation 
has  failed,  a  bridge  having  been  constructed  across  the  centre  of  the 
fissure,  leaving  a  cleft  posteriorly  and  a  perforation  anteriorly.  The 
instrument  for  such  a  case  may  be  a  hard-rubber  bulb  which  passes 
through  the  anterior  opening,  filling  the  posterior  cleft  and  reaching  to 


724  PALATAL  MECHANISM. 

the  pharyngeal  wall  during  the  act  of  speaking.  Such  a  bulb  is  hinged 
to  the  plate,  and  it  necessarily  rises  and  falls,  because  it  rests  upon  the 
upper  side  of  the  surgical  bridge,  and  the  levator  muscles  cannot  elevate 
the  halves  of  the  divided  palate  without  raising  this  bridge  and  with  it 
the  extension  which  carries  the  obturator.  It  is  rare  that  such  an  ante- 
rior opening  will  permit  the  passage  of  the  hard  bulb,  though  such  cases 
have  been  treated. 

The  history  of  an  instructive  case  which  passed  through  the  writer's 
hands  a  few  months  ago  is  here  given.  Before  describing  this  case  refer- 
ence must  be  made  to  another  sort  of  obturator  which  had  been  employed 
in  this  instance.  The  object  in  hinging  a  hard-rubber  obturator  is  to 
furnish  an  instrument  which  will  simulate  the  action  of  the  artificial 
velum.  In  Germany  the  same  result  had  been  sought  in  a  different 
manner,  I  do  not  know  who  claims  to  be  the  inventor  of  the  method, 
but  the  one  which  was  seen  in  this  case  was  made  by  Dr.  C.  Schultsky 
of  Berlin.  This  was  merely  a  soft-rubber  obturator — in  other  words,  a 
soft-rubber  bulb — hollow  like  the  hard-rubber  bulbs,  but  so  fashioned 
that  it  could  be  inflated  something  after  the  manner  of  the  pneumatic 
bicycle  tire.  The  idea  evidently  is  that  the  soft-rubber  ball,  placed  in 
the  back  of  the  throat,  may  be  compressed  by  the  muscles,  thus  serving 
to  fill  the  gap  under  all  circumstances.  The  history  of  the  patient  is  as 
follows  : 

Mr.  F was  born  in  Posen,  Germany,  in  1861,  and  was  thirty- 
four  years  of  age  when  he  presented  himself  for  treatment.  At  birth  he 
had  a  fissure  of  the  soft  palate  which  reached  forward  to  the  border  of 
the  hard  palate,  but  did  not  extend  into  the  bone.  Nevertheless,  he  had 
a  hare-lip,  which  was  operated  upon  during  infancy  with  but  partial  suc- 
cess, an  opening  being  left  near  the  nostril.  At  thirteen  Dr.  Suersen 
made  for  him  an  obturator  having  a  hard-rubber  bulb.  This  was  worn 
for  a  year,  when  the  clasp  on  one  side  was  broken  and  the  fixture  was 
abandoned.  At  the  age  of  twenty  Prof.  Wolf  of  Berlin  accepted  him  as 
a  patient  at  his  private  clinic  and  undertook  to  close  the  cleft  surgi- 
cally, and  at  the  same  time  performed  a  supplementary  operation  on  the 

lip.     This  latter  operation  was  a  complete  success,  and  Mr.  F —  has 

now  a  good  lip  both  in  appearance  and  usefulness.  A  heavy  moustache 
almost  completely  covers  the  scar,  so  that  there  is  no  external  evidence 
of  his  deformity  The  operation  upon  the  cleft,  however,  was  another 
addition  to  the  list  of  cases  where  the  failure  of  surgical  measures  has 
rendered  the  dentist's  work  more  complicated,  without  compensating 
advantage  to  the  patient.  The  cleft  originally  extended  to  the  border 
of  the  hard  palate,  so  that  it  would  have  been  comparatively  simple  to 
provide  for  him  an  artificial  velum  similar  to  that  shown  in  Figs.  963 
and  964.  After  learning  to  speak  he  could  then  have  had  an  obturator 
should  he  have  desired  it.  The  operation,  however,  by  partly  closing 
the  cleft  constructed  a  bridge  of  soft  tissue  over  which  a  plate  could  not 
be  worn,  so  that  it  became  necessary  to  have  an  extension  to  the  plate 
which  should  carry  the  appliance  used  to  fill  the  gap.  Thus  the  patient 
was  very  much  worse  off  after,  than  before  his  operation.  A  year  later  he 
placed  himself  under  the  care  of  a  dentist,  Dr.  C.  Schultsky  of  Berlin,  who 
made  for  him  a  soft-rubber  obturator.  All  that  remains  of  this  instrument 
is  shown  in  Fig.  971.     This  consists  of  a  vulcanite  plate  clasped  to  the. 


CLEFT  PALATE. 


725 


natural  teeth  and  carrying  a  few  artificial  teeth.    Immediately  at  the  pos- 
terior border  is  a  small  extension  [a),  also  of  vulcanite,  which  is  connected 


Fig.  971. 


with  the  plate  proper  by  a  gold  slide  (6)  which  moves  forward  and  back- 
ward in  a  metal  slot,  thus  providing  for  antero-posterior  movement.  Next 
there  is  a  gold  spiral  spring  (c),  which  permits  the  obturator  to  follow  the 
play  of  the  muscles  in  any  direction.  At  the  posterior  end  of  the  gold 
spring  was  permanently  fastened  a  soft-rubber  bulb  or  ball  [d).  Judging 
from  what  was  left  of  this  bulb,  it  may  be  inferred  that  originally  it  was 
quite  thick  along  that  portion  which  formed  the  palatal  surface  and  was 
intended  to  complete  the  arch  of  the  vault.  Into  this  thick  portion  the 
spring  was  fastened.  Thinner  walls  extended  upward,  completing  the 
bulb  and  leaving  it  hollow.  There  was  some  sort  of  orifice  and  stop- 
valve,  inadequately  described  by  the  patient,  through  which  he  was 
instructed  to  inflate  the  bulb  every  morning,  the  air  gradually  escaping 
during  the  day. 

He  wore  this  instrument  for  five  years ;  during  this  time,  however, 
the  bulb  burst,  whereupon  he  continued  to  wear  it  in  its  ruptured  condi- 
tion. Then  he  had  a  second  bulb  attached  by  the  same  dentist,  which 
after  a  brief  time  also  burst.  Nevertheless,  he  continued  to  use  this 
appliance  for  eight  years  more,  and  the  figure  shows  the  fixture  as  I 
found  it.  Two  facts  in  connection  with  this  case  are  peculiarly 
instructive  :  so  long  as  the  original  bulb  remained  whole  there  was  no 
improvement  in  the  patient's  speech ;  second,  after  it  had  burst  he 
noticed  a  very  rapid  change,  and  Avithin  two  years  he  was  speaking  with 
approximate  correctness.  Thus  the  ruptured  bulb  was  better  than  the 
soft-rubber  obturator  which  it  was  intended  to  be ;  and  the  point  of 


726 


PALATAL  MECHANISM. 


great  interest  here  is  that,  though  in  a  very  crude  way,  still  in  principle, 
the  bulb  became  a  Kmgsley  soft  velum  as  soon  as  it  was  ruptured.  This 
can  be  better  comprehended  by  comparing  Fig.  971  (Dr.  Schultsky's 
instrument  with  bulb  ruptured)  with  Fig.  972  (which  shows  the  appli- 
ance constructed  for  him  by  the  writer).  It  will  be  seen  at  a  glance 
that  the  velum  here  appears  to  differ  from  the  typical  form  shown  in 
Figs.  960,  961,  and  962  in  that  there  is  but  a  single  flap.  It  is  there- 
fore necessary  to  explain  how  it  is  that  the  principle  is  the  same  though 
the  form  is  different.  The  typical  velum  has  two  flaps,  one  of  which 
lies  in  the  upper  cavity  resting  upon  the  sides  of  the  cleft,  while  the 
lower  flap  is  below,  the  two  forming  grooves  in  which  the  sides  of  the 

Fig.  972. 


cleft  move.     When  closed,  the  uvulse,  or  extreme  posterior  ends  of  the 
split   velum,  approximate   one   another,  hugging   the   artificial   velum 

closely. 

Fig.  973. 


Fig.  973  shows  a  model  of  Mr.  F 's  mouth,  and  the  absence  of  the 

uvulse  will  be  observed.     The  uvulte  were  originally  present,  but  were 
destroyed  by  the  surgical  operation,  and  the  sides  of  the  cleft  poste- 


CLEFT  PALATE. 


727 


riorly  are  now  continuous  with  the  pillars  of  the  fauces.  Here,  there- 
fore, there  was  no  need  for  grooves,  there  being  no  possibility  of  the 
close  approach  of  the  sides  of  the  cleft.  A  single  flap  was  made^  such 
as  is  shown  in  Fig.  972.  The  anterior  edges  were  made  heavie/  than 
usual,  to  offer  sufficient  resistance  to  ensure  the  raising  of  the  hinge  ex- 
tension which  connected  the  velum  with  the  plate  in  the  roof  of  the 
mouth.  The  single  flap  is  similar  in  the  theory  of  its  office  to  the  single 
flap  of  Dr.  Sercombe,  but  modified  to  assume  the  more  practical  form 
seen  in  the  upper  flap  of  the  Kingsley  velum.  Dr.  Sercombe  claimed 
that  the  flap  should  not  reach  the  posterior  wall  of  the  pharynx ;  in  this 
he  made  a  grave  error. 

Here,  tlien,  may  be  indicated  the  reason  why  the  hinge  is  of  no 
value  with  an  obturator,  and  yet  becomes  a  necessity  with  such  a  case 
as  the  last  two — viz.  where  the  apex  of  the  fissure  is  distant  from  the 
posterior  border  of  the  hard  palate.  Obturators  are  constructed  of 
hard  rubber,  have  sloping  sides,  and  are  highly  polished.  In  the 
efforts  to  close  the  cavity  of  the  nares  the  levator  muscles  draw  the  sides 
of  the  cleft  upward  and  slightly  backward,  and  if  a  patient  can  be  made 
to  swallow  with  the  mouth  open,  the  operator  will  readily  discover  that 
the  tissues  slide  along  the  smooth  sides  of  the  obturator,  but  do  not 
raise  it.  The  hinge,  therefore,  is  useless.  With  the  other  condition  a 
totally  different  result  obtains.  The  soft  velum,  lying  entirely  upon  the 
upper  surface  of  the  cleft,  and  the  anterior  edge  of  the  velum  being  stiff" 
and  wide,  while  the  apex  of  the  fissure  presents  the  usual  angle,  it  fol- 

FiG.  974. 


lows  that  the  natural  palate  cannot  rise  without  carrying  the  superincum- 
bent velum  with  it.  This  it  could  not  accomplish  if  the  extension  which 
connects  the  velum  with  the  plate  were  unyielding.     Consequently,  the 


hinge  is  a  positive  necessity. 


Fig. 


974  shows  the  model  of  Mr.  F- 


728  PALATAL  MECHANISM. 

with  appliance  in  position,  the  dotted  line  indicating  the  border  of  the 
velum,  which  is  above  the  fissured  sides  of  the  palate,  and  making  it 
clear  that  no  movement  can  displace  it,  while  the  least  retraction  of  the 
tissues  must  be  followed  by  a  responsive  movement  of  the  velum  and 
the  hinged  extension.  In  the  figure  the  velum  is  seen  at  a  and  the 
hinge  at  b.  The  plate  in  this  instance  was  made  of  vulcanite  to  suit 
the  wishes  of  the  patient,  his  original  plate  having  been  of  that  mate- 
rial.    Metal  would  have  been  preferable. 

Fig.  975  is  of  special  interest :  it  shows  a  similar  instrument  having 
a  hinged  extension,  but  the  soft  velum  is  of  the  typical  form,  because, 

Fig.  975. 


although  there  was  a  great  space  between  the  border  of  the  hard  palate 
and  the  apex  of  the  fissure,  thus  necessitating  the  hinged  extension, 
nevertheless  the  fissure  itself  was  fairly  regular,  the  uvulse  being  pres- 
ent, and  the  two  sides  of  the  cleft  when  shutting  off  the  cavity  of  the 
nares  working  co-ordinately.  The  model  of  this  case  is  seen  in  Fig. 
958,  while  the  instrument  with  tiny  velum  is  shown  in  Fig.  975.  In 
connection  with  hinged  artificial  palates  it  is  also  of  interest  to  record  the 
fact  that  this  case  was  treated  by  Dr.  Kingsley  some  twenty  years  ago. 

Taking  the  Impression  op  Olept  Palate. 

No  appliance  made  by  the  dentist  needs  to  be  more  accurately  fitted 
than  an  artificial  palate.  It  is  obviously  a  corollary,  therefore,  that  the 
plaster  model  should  be  as  nearly  as  possible  an  exact  reproduction  of 
the  mouth  which  it  represents. 

To  obtain  such  a  model  requires  skill,  but  not  more  than  should  be 
possessed  by  the  qualified  practitioner.  Yet  the  difficulty  of  taking  the 
impression  is  the  obstacle  which  has  hindered  many  from  attempting  to 
treat  these  cases,  while  the  ultimate  failure  of  many  others  who  have 
essayed  to  make  instruments  is  directly  traceable  to  their  inaccuracy  in 
this  initial  step. 

The  ordinary  impression  taken  for  artificial  dentures  is  easy,  because  a 
model  is  required  only  of  that  portion  of  the  mouth,  the  tissues  of  which 
overlie  bone.  Therefore,  whether  the  impression  material  be  introduced 
hot  or  cold,  hard  or  soft,  in  large  or  small  quantity,  the  resultant  im- 
pression is  approximately  the  same,  because  of  the  resistance  oflFered  by 
the  roof  of  the  mouth  against  which  it  is  pressed.  When,  however,  too 
much  material  is  carried  into  the  mouth,  so  that  it  extends  beyond  the 
border  of  the  hard  palate,  the  common  experience  is  what  is  called  "  gag- 
ging." A  consideration  of  what  tliis  "gagging"  is,  will  make  more 
readily  understood  a  fundamental  principle  involved  in  all  cleft-palate 
cases. 

The  soft  palate  is  sensitive,  and  when  the  impression  material  is 
brought  into  contact  with  it,  the  result  is  an  irritation  or  tickling,  where- 


TAKING   THE  IMPRESSION  OF  CLEFT  PALATE.  729 

upon  the  involuntary  muscles  of  the  throat  endeavor  to  draw  the  parts 
away  from  the  intruding  substance.  Thus  the  velum  is  elevated,  and 
consequently  were  a  model  to  be  made  from  such  an  impression  it  would 
be  inaccurate  as  to  the  posterior  portion  of  the  mouth,  in  that  it  would 
not  be  a  representation  of  the  parts  at  rest. 

With  the  velum  divided  as  in  cleft  palate,  the  disturbance  of  these 
sensitive  tissues  upon  the  introduction  of  the  impression  material  is  even 
greater.  The  two  halves  of  the  soft  palate  are  not  only  drawn  upward, 
but  they  also  approach  each  other.  Thus  the  resultant  model  will  show 
the  cleft  narrower  than  it  really  is  when  the  parts  are  at  rest,  and  the  pose 
of  the  divided  palate  will  be  wrong,  so  that  no  proper  calculation  can  be 
made  for  restoring  the  true  arch  of  the  vault.  This  will  obtain  whether 
the  impression  be  taken  with  plaster  of  Paris,  or  with  impression  com- 
pound softened  by  heat.  Where  the  impression  comi)ound,  however,  is 
not  very  soft,  or  where  the  divided  palate  is  lacking  in  vital  response, 
the  impression  material  will  merely  press  the  soft  tissues  before  it,  the 
final  model  being  absolutely  worthless. 

Thus  it  is  seen  that  no  one  can  obtain  an  absolutely  accurate 
impression  of  the  divided  velum  in  its  normal  pose.  Nevertheless,  a 
model  may  be  made  which  will  be  as  accurate  as  any  model  of  the  mouth 
can  be. 

The  method  of  procedure  is  as  follows:  Select  an  impression-tray  of 
the  ordinary  form,  just  large  enough  to  embrace  the  arch  without  stretch- 
ing the  mouth,  and  long  enough  to  reach  slightly  beyond  the  posterior 
border  of  the  hard  palate.  In  the  majority  of  cases  this  will  answer  all 
purposes,  but  occasionally  it  may  be  advantageous  to  extend  the  cup  by 
adding  to  it  a  flap  of  sheet  gutta-percha.  This  may  be  carried  back  as 
far  as  the  uvula,  but  should  not  touch  the  velum  at  any  point.  This  is 
to  be  ascertained  by  introducing  the  cup  empty. 

Plaster  of  Paris  is  mixed  in  the  usual  way,  a  little  salt  being  added 
to  hasten  the  setting,  and  warm  water  used  to  render  it  more  acceptable 
to  the  mouth.  A  pinch  of  powdered  vermilion  will  color  the  impres- 
sion, which  will  aid  in  separating,  and  is  preferable  to  placing  the  color 
in  the  plaster  for  the  model.  The  plaster  is  placed  in  the  tray  in  quan- 
tity proportionate  to  the  height  of  the  roof,  less  being  used  where  the 
cleft  is  in  the  velum  only,  than  where  the  fissure  enters  the  hard  palate 
also.  The  use  of  too  much  plaster  is  to  be  avoided,  lest  it  escape  and 
trickle  down  the  throat.  The  impression-tray  is  to  be  carried  into  the 
mouth  just  as  the  plaster  gives  evidence  of  setting,  and  is  pressed  up 
quickly  and  firmly,  and  then  held  steadily  until  sufficiently  hard  for 
removal.  With  a  little  practice  the  calculation  can  be  made  with  such 
nicety  that  the  time  required  will  be  not  more  than  one  minute.  The 
plaster  which  remains  in  the  vessel  in  which  it  was  prepared  will  be  a 
guide  to  its  setting,  and  as  soon  as  it  will  fracture  sharply  the  impres- 
sion should  be  withdrawn. 

Where  the  fissure  extends  into  the  hard  palate  it  will  occasionally 
occur  that  the  plaster  which  passes  up  into  the  nasal  cavity  cannot  be 
withdrawn  with  the  impression  ;  but  if  the  impression  be  removed  at 
the  proper  moment,  the  plaster  will  fracture  along  the  line  of  the  fissure, 
and  that  portion  left  up  in  the  nares  may  be  taken  away  with  the 
tweezers. 


730 


PALATAL  MECHANISM. 


Fig.  976. 


Before  passing  to  a  consideration  of  constructing  the  model  one  or 
two  other  points  in  relation  to  the  impression  are  to  be  considered. 

Ordinarily,  all  that  is  required  in  a  model  from  which  to  make  an 
instrument  for  a  cleft-palate  patient  will  be  absolute  accuracy  as  to  the 
oral  aspect  of  the  parts  and  the  borders  of  the  fissure  from  its  apiex  to 
the  uvulae.  It  will  very  rarely  be  essential  to  procure  a  perfect  impres- 
sion of  the  upper  or  nasal  side,  except  that  the  ope- 
rator should  observe  the  thickness  of  the  tissues 
along  the  borders  of  the  cleft,  the  position  of  the 
vomer,  and  Avhether  it  is  likely  to  interfere  with  the 
design  of  the  instrument,  as  it  often  will  where  the 
fissure  only  slightly  enters  the  hard  palate.  In  such 
cases  it  becomes  important  to  know  how  close  the 
insertion  of  the  vomer  is  to  the  border  of  the  cleft 
at  the  apex.  This  is  readily  accomplished  by  pla- 
cing a  small  quantity  of  plaster  up  into  the  nasal 
cavity  at  the  apex  of  the  fissure,  carrying  it  into 
place  with  a  narrow-bladed  knife,  or  other  suitable 
instrument,  just  before  introducing  the  impression. 
This  may  come  away  with  the  impression,  or  it 
may  fracture  and  remain  in  place,  in  which  case 
it  is  to  be  removed  with  tweezers  and  added  to  the 
impression. 

A  method  of  obtaining  the  impression  of  the 
upper  nares  is  described  in  the  American  System 
of  Dentistry  as  follows  :  "  This  impression,  if  prop- 
erly obtained,  will  show  a  distinct  outline  of  the 
cleft  and  uvula.  The  portion  of  the  plaster  occupy- 
ing the  fissure  or  cleft  is  next  cut  down  to  a  smooth 
surface,  and  a  little  forward  of  the  median  line  of 
the  cleft  a  hole  is  drilled  through  the  cup  and 
impression ;  in  addition  to  this,  two  pits  are  made 
in  the  smooth  surface  which  represent  the  cleft,  in 
the  same  manner  as  would  be  done  in  a  cast  for  a 
spider  articulator,  to  receive  corresponding  elevations 
in  the  second  half  of  the  impression.  The  whole 
surface  of  the  impression  is  then  painted  with  san- 
darac  varnish,  vaseline,  or  solution  of  soap  to  prevent 
adhesion.  The  next  procedure  is  to  pass  a  rubber 
tube  through  the  hole  in  the  impression,  replace  it 
in  the  mouth,  one  end  of  the  tube  extending  through- 
on  to  the  nasal  surface,  the  other  being  carried  for- 
ward and  held  with  the  cup  in  position  by  an  assistant. 
In  the  outer  end  of  the  tube  is  placed  the  nozzle  of  a 
syringe  ;  a  two-ounce  vaginal  syringe  answers  the 
purpose  (Fig.  976).  After  withdrawing  the  piston  the  required  quantity 
of  plaster  should  be  mixed  to  the  consistency  of  cream  in  a  vessel  with  a 
spout,  by  which  it  can  be  poured  into  the  syringe.  These  preparations 
having  been  made,  the  assistant  is  instructed  to  hold  the  syringe  in  posi- 
tion, and  the  plaster  is  poured  into  it  and  the  piston  replaced.  Slight 
pressure  on  the  handle  will  force  the  plaster  through  the  rubber  tube  on 


TAKING   THE  IMPRESSION  OF  CLEFT  PALATE.  731 

to  the  smooth  surface  and  adjacent  parts  of  the  impression  already  taken, 
ihe  patient  being  instructed  to  incline  the  head  forward  if  the  plaster  is 
felt  to  be  running  down  the  throat,  or  backward  if  it  runs  too  far  in  the 
opposite  direction,  the  object  being  to  keep  it  on  a  level  if  possible. 

"  Precaution  should  be  taken  before  the  plaster  sets  to  remove  the 
rubber  tube  and  syringe  and  cleanse  them  thoroughly  for  future  use. 
When  the  impression  is  ready  for  withdrawal— and  it  is  not  necessary 
for  the  plaster  to  set  very  hard — remove  the  lower  or  palatal  portion 
with  the  cup;  the  nasal  portion  can  be  readily  withdrawn  afterward 
with  a  pair  of  tweezers." 

If  this  method  is  intended  to  be  utilized  in  cases  where  the  fissure  is 
exclusively  in  the  soft  palate,  it  is  lacking  in  utility, /or  no  possible  occa- 
sion for  an  impression  of  the  nasal  cavity  is  conceivable,  the  position  of 
the  vomer  and  turbinated  bones  being  normal,  and  the  artificial  palate 
never  needing  to  reach  farther  forward  than  the  apex  of  the  fissure. 

Where  the  fissure  partly  enters  the  hard  palate,  as  has  been  already 
stated,  the  exact  position  of  the  vomer  must  be  comprehended.  The 
reason  is  that  where  an  artificial  velum  is  used,  it  engages  the  fissure,  so 
that  a  flap  extends  slightly  over  the  border  at  the  apex  on  the  nasal  side. 
In  some  cases  the  insertion  of  the  vomer  into  the  hard  palate  is  so  near 
to  the  border  at  the  apex  that  the  artificial  velum  might  rest  against  it 
and  cause  irritation,  unless  provision  be  made  to  guard  against  this. 
But  the  simple  method  of  carrying  a  little  plaster  through  the  fissure 
at  this  point  before  inserting  the  impression,  as  previously  described, 
accomplishes  the  required  result  perfectly,  without  resort  to  such  an 
intricate  process  as  the  one  quoted. 

Where  the  fissure  involves  the  whole  or  greater  part  of  the  hard 
palate  it  may  occasionally  be  required  to  secure  an  accurate  model  of 
the  nasal  cavity  as  well  as  of  the  oral.  An  example  of  such  an  instance 
is  shown  and  described  in  connection  with  Figs.  909  and  910. 

The  impression  here  is  obtained  by  carrying  the  plaster,  mixed  fairly 
stiff,  up  into  the  nasal  cavity,  filling  it  to  the  borders  of  the  fissure, 
whereupon  the  tray  with  additional  plaster  is  carried  to  place.  As  the 
plaster  in  the  tray  unites  with  that  which  is  in  the  nares,  great  care 
must  be  observed  to  remove  the  impression  at  the  first  moment  when  a 
sharp  fracture  is  possible.  With  a  sudden  sharp  movement  the  impres- 
sion comes  away,  leaving  the  plaster  in  the  nares,  the  fracture  along  the 
borders  of  the  fissure  being  sharp  and  clean,  so  that,  when  the  nasal 
portion  is  removed  by  sliding  it  back  toward  the  throat  and  allowing 
it  to  drop  down  upon  the  tongue,  it  is  readily  replaced  in  proper  posi- 
tion upon  the  impression.  If  the  operator  is  timid  about  attempting 
this,  after  filling  the  nares  with  plaster  he  may  allow  it  to  set.  Then 
after  oiling  the  exposed  portion  of  the  plaster,  which  now  finishes  out 
the  arch  of  the  roof,  the  impression  may  be  completed  without  danger 
of  the  two  parts  adhering. 

In  accidental  fissures  resulting  from  disease  or  other  cause  we  some- 
times find  merely  an  aperture  in  the  palate,  which  may  be  quite  small. 
In  taking  an  impression  the  plaster  would  ooze  through  this  hole  and 
form  a  knob  or  button  upon  the  upper  side,  which  of  course  would 
remain  after  the  removal  of  the  impression-cup.  Then,  as  the  posterior 
portion  of  the  soft  palate  would  be  normal,  it  might  become  a  very  dif- 


732  PALATAL  MECHANISM. 

ficult  matter  to  remove  this  plaster  without  permitting  it  to  pass  down 
into  the  pharynx.  In  these  cases  the  precaution  should  be  taken  to  lay 
across  the  aperture  a  bit  of  Japanese  tissue-paper  folded  two  or  three 
times.  This  paper  will  yield  sufficiently  to  allow  the  plaster  to  take  a 
perfect  impression,  yet  resists  its  passage  through. 

The  model  made  from  the  most  accurate  impression  will  represent 
the  cleft  with  its  sides  drawn  somewhat  together  and  possibly  pressed 
backward.  The  next  step,  therefore,  will  be  the  correction  of  these 
errors,  and  the  production  finally  of  a  model  which  will  be  an  accurate 
reproduction  of  the  mouth. 

A  trial-plate  made  upon  the  model,  with  an  extension  fitting  into  the 
fissure,  will  indicate  at  once,  when  carried  to  the  mouth,  how  much  wider 
the  natural  cleft  is  when  the  parts  are  at  rest.  The  natural  cleft  is  to 
be  observed  closely  in  connection  with  this  trial-plate,  and  the  cleft  in 
the  model  is  widened  and  altered  by  cutting  away  the  plaster  with  a 
knife  until  a  trial-plate  which  exactly  follows  the  outlines  of  the  cleft 
on  the  model  will  similarly  fit  the  cleft  in  the  mouth.  At  the  same  time 
the  edges  of  the  cleft  in  the  model  may  be  rounded,  and  the  pitch  of  the 
palate  corrected  to  agree  with  the  mouth,  by  adding  plaster  with  a  small 
camel's-hair  brush.  In  the  end  the  model  will  not  only  appear  to  agree 
with  the  mouth,  but  the  trial-plate  will  demonstrate  that  it  does  agree. 
It  is  not  guesswork,  but  absolute  accuracy,  even  the  bulbs  of  the  uvulae 
being  perfectly  reproduced. 

The  Making  of  Artificial  Vela. 

With  an  accurate  model  from  which  to  work  an  artificial  velum  could 
be  made  without  further  reference  to  the  patient,  though  it  might  be 
best  for  the  inexperienced  to  try  in  the  model  of  the  velum  before  pro- 
ceeding to  the  construction  of  metal  moulds. 

The  first  step  in  the  production  of  the  artificial  velum  will  be  to  make 
a  model  of  the  palatal  flap.  The  model  of  the  velum,  if  it  is  not  to  be 
tried  in  the  mouth,  may  be  made  of  wax,  otherwise  it  will  be  best  to  use 
sheet  gutta-percha.  The  palatal  flap  is  a  triangle  with  rounded  angles. 
The  apex  of  this  triangle  coincides  with  the  apex  of  the  fissure,  and  the 
base  extends  across  from  one  uvula  to  the  other.  This  flap  should  be 
made  just  large  enough  to  bridge  the  gap,  as  it  will  be  easy  to  widen  it 
later  by  scraping  the  mould  should  it  become  needful,  whereas  if  made 
too  large  at  the  outset  it  might  become  necessary  to  make  a  part  of  the 
mould  over.  The  pattern  of  the  flap  having  been  cut  out  from  gutta- 
percha, it  is  to  be  slightly  softened  and  then  pressed  against  the  model, 
so  that  it  assumes  the  proper  form  to  lie  close  to  the  surface  of  the  latter. 
It  will  often  occur  that  the  edges  of  the  natural  cleft  are  rounded  or 
rope-like,  thus  showing  a  depression  between  the  border  of  the  cleft 
and  the  maxillary  bone.  In  these  cases  the  upper  flap,  when  moulded 
upon  the  model,  will  assume  quite  a  curl  or  crimp,  especially  near  the 
uvulae.  If  the  model  is  accurate  and  the  flap  is  made  to  properly  conform 
to  this  peculiarity,  when  placed  in  the  mouth  it  will  lie  close  against  the 
soft  tissues.  Were  it  left  comparatively  a  plane,  the  edges  would  stand 
off  and  be  quite  noticeable  to  the  tongue.  This  curling  is  made  more 
apparent  because  of  the  fact  that  the  flap  is  slightly  depressed  between 


THE  MAKING   OF  ARTIFICIAL    VELA. 


733 


the  sides  of  the  cleft,  so  that  it  forms  a  part  of  the  arch  of  the  mouth 
and  completes  it.  As  soon  as  the  flap  has  been  moulded  into  proper 
form,  all  the  edges  being  quite  thin,  it  is  plunged  into  cold  water,  so 
that  it  shall  retain  its  shape. 

The  second  or  upper  flap  is  moulded  upon  the  model  in  a  similar 
manner,  the  form  being  again  triangular.  But  the  base  must  now  be 
fashioned  so  that  its  posterior  edge  will  meet  the  ridge  of  the  pharynx 
at  a  slight  angle.  The  general  adaptation  of  the  flap  to  the  model  having 
been  obtained,  it  is  placed  in  position,  and  the  model  and  flap  firmly  held 
in  the  left  hand,  while  with  the  thumb  and  fore  finger  of  the  right  hand 
the  operator  grasps  the  flap  at  the  centre  of  the  posterior  part  and  simply 
bends  it  up,  whereupon  it  asumes  the  form  shown  in  Figs.  960,  961,  and 
962.  Usually  the  guide  for  bending  this  tail-piece  is  to  form  it  so  that 
the  plane  of  that  surface  will  be  on  a  line  with  the  incising  edges  of  the 
anterior  teeth. 

The  two  flaps  are  next  placed  upon  the  model  at  the  same  time  and 
waxed  together  with  hard  wax.  The  velum  is  then  ready  to  be  tried  in 
the  mouth,  when  the  operator  may  correct  any  discrepancies  as  to  fit  or 
length. 

The  model  of  the  velum  having  been  satisfactorily  made,  it  becomes 
necessary  to  produce  metal  moulds  in  which  soft  rubber  may  be  vulcan- 
ized into  the  desired  form. 

Fig.  977. 


A  convenient  form  of  flask  for  holding  these  moulds  is  round  and  in 
two  parts,  one  of  which  has  a  square  hole  cut  at  the  centre. 

In  constructing  the  moulds  the  model  of  the  velum  is  placed  in  that 
half  of  the  flask  which  has  the  hole,  so  that  the  smaller  or  palatal  flap 


734 


PALATAL  MECHANISM. 


rests  over  the  hole.  The  flask  having  been  freely  oiled,  plaster  is  poured 
into  it  and  around  the  model.  When  hard  it  is  knocked  out  readily  and 
carved  into  shape.  It  is  then  varnished,  replaced  in  the  flask,  and  oiled. 
The  model  of  the  velum  still  being  in  position,  plaster  is  poured  over  it 
and  the  plaster  mould,  which  now  surrounds  it,  and  the  opposite  half  of 
the  flask,  well  oiled,  is  put  on  and  pressed  flrmly  to  place.  When  this 
is  hard  and  separated  the  two  parts  of  the  mould  are  complete.  The 
third  is  made  by  pouring  plaster  through  the  hole  in  the  top  of  the  flask, 

Fig.  978. 


completely  filling  the  space  left  within  the  flask,  and  covering  the  top 
flap.  These  three  pieces  of  plaster  are  then  reproduced  by  moulding  in 
sand  and  casting  in  type-metal.  The  general  appearance  when  complete 
is  shown  in  the  accompanying  illustrations.  Fig.  977  is  the  bottom-piece, 
in  which  a  pin  appears :  this  is  best  made  of  iridio-platinum  wire,  and 
is  driven  into  a  drilled  hole  after  the  mould  is  cast.  In  some  cases  it 
will  be  tight  enough,  but  occasionally  it  may  be  requisite  to  fasten  it 
Avith  soft  solder.  Its  purpose  is  to  produce  a  hole  in  the  velum  through 
which  the  bar  on  the  plate  passes.  The  two  aspects  of  the  central 
piece  of  the  mould  are  shown  in  Figs.  978  and  979,  while  Fig.  980 
shows  the  top-piece. 

The  surfaces  for  moulding  the  rubber  are  to  be  smoothed  with  a  pine 
stick  and  pumice.  The  metal  moulds  are  returned  to  their  respective 
positions  in  the  flask  sections. 

In  vulcanizing  the  soft  rubber  it  is  well  to  slightly  soap  the  surface 
of  the  moulds  before  packing,  as  this  facilitates  removal  after  vulcaniza- 
tion, and  avoids  a  tendency  on  the  part  of  the  rubber  to  adhere  to  the 
metal,  especially  should  any  rough  places  be  left,  which  of  course  should 
be  avoided. 


THE  MAKING   OF  ARTIFICIAL   VELA. 

Fig.  979. 


735 


The  flask  should  be  opened  and  excess  of  rubber  removed  ;  otherwise 
it  will  be  pressed  against  the  unpolished  portions  of  the  mould,  and  ren- 


FiG.  980. 


der  it  extremely  difficult  to  open  the  flask  after  vulcanization.     As  soft 
rubber  swells  considerably  during  vulcanization,  the  mould  need  not  be 


736  PALATAL  MECHANISM. 

quite  full,  but  care  should  be  taken  to  avoid  creases  in  the  rubber,  as 
they  will  not  be  filled  out  however  much  the  rubber  may  swell,  probably 
owing  to  the  imprisonment  of  air. 

The  best  results  in  the  vulcanization  of  soft  rubber  are  obtained  by 
observing  the  following  directions  :  Place  charcoal  or  other  substance  in 
the  bottom  of  the  vulcanizer  high  enough  to  stand  above  the  water  which 
is  poured  in.  Allow  the  flask  to  rest  upon  this  charcoal.  In  this  man- 
ner the  rubber  is  vulcanized  in  steam. 

The  thermometer  which  registers  the  heat  should  indicate  240°  for 
two  hours ;  250°  for  one  hour ;  260°  for  one  hour ;  and  270°  for  one 
hour. 

The  velum  when  taken  from  the  flask  will  have  a  peculiar  odor  if 
overdone,  as  though  it  had  been  burned.  In  that  case,  however  perfect 
and  elastic  it  may  appear,  it  will  be  worthless  within  a  very  few  weeks. 

The  Construction  of  an  Obturator. 

An  obturator  may  be  made  for  a  patient  where  the  cleft  involves  the 
soft  palate  only,  but  will  be  more  commonly  resorted  to  where  both  soft 
and  hard  palates  are  fissured.  The  process  in  connection  with  the  latter 
condition  is  described,  as  it  is  the  more  intricate. 

A  correct  model  having  been  obtained,  the  fissure  in  the  hard  palate 
is  filled  with  wax,  so  that  the  arch  of  the  vault  is  restored.  Dies  are 
made  and  a  plate  of  iridio-platinum  swaged  to  fit  this  reconstructed 
model,  with  the  result,  of  course,  that  when  carried  to  the  mouth  it 
bridges  over  the  gap  in  the  hard  palate.  The  plate  is  provided  with  an 
extension  at  the  posterior  part  which  shall  support  the  obturator,  and  it 
is  attached  to  the  teeth  by  gold  clasps.  For  this  purpose  it  is  best  to 
rely  upon  the  sixth-year  molars  as  ofl'ering  the  best  anchorage,  and  where 
these  teeth  are  badly  decayed  it  is  often  advisable  to  crown  them 
with  gold  before  fitting  the  clasps  about  them.  Thus  the  anchorages 
may  be  permanently  protected  against  loss  by  decay. 

No  matter  how  valuable  teeth  may  be  to  ordinary  persons,  they  are 
doubly  so  to  the  cleft-palate  patient,  who  must  depend  upon,  them  not 
alone  for  mastication,  but  also  for  speech,  since  they  serve  to  sustain  the 
instrument  which  enables  him  to  overcome  his  infirmity. 

The  metal  plate  and  clasps  having  been  accurately  fitted  to  the  mouth, 
a  loop  of  copper  wire  is  soldered  temporarily  to  the  upper  side  of  the 
plate  (with  soft  solder)  and  extended  backward  about  two-thirds  the 
length  of  the  fissure.  The  object  of  this  is  to  hold  a  mass  of  impression 
material  which  is  to  be  used  for  forming  the  model  of  the  obturator. 
This  mass  of  impression  material  is  wrapped  about  the  wire  loop  and 
then  fashioned  into  the  general  shape  of  the  fissure,  when  it  is  hardened 
in  cold  water.  A  trial  in  the  mouth  will  indicate  wherein  it  must  be 
altered  by  trimming  with  a  sharp  knife.  The  mass  having  been  brought 
to  an  approximation  of  the  proper  form  after  this  manner,  it  is  then 
slightly  softened  in  warm  water  and  again  placed  in  the  mouth,  where- 
upon the  patient  is  directed  to  swallow  several  times.  This  compels 
the  levator  and  constrictor  muscles  to  close  upon  the  softened  mass  and 
mould  it  into  such  shape  as  will  be  required  to  enable  the  patient  to 
completely  close  the  opening  to  the  nares.     Upon  removal  the  mass  will 


THE  CONSTRUCTION  OF  AN  OBTURATOR. 


737 


have  assumed  an  irregular  shape,  which  now  must  be  altered  to  furnish 
the  final  model  of  the  obturator.  The  palatal  surface  is  trimmed  into  a 
continuous  flat  surface,  so  that  in  connection  with  the  plate  the  arch  of 
the  vault  is  completed  and  the  gap  in  the  back  of  the  mouth  bridged 
over.  The  upper  surface  is  similarly  cut  away,  and  is  usually  best 
formed  with  a  depression  curved  laterally,  experience  having  taught  that 
such  a  form  is  best  adopted  for  the  obliteration  of  the  nasal  quality  of 
the  voice.  Thus  the  sides  and  the  posterior  end  are  left  undisturbed  as 
they  were  moulded  by  the  action  of  the  muscles. 

It  must  be  remembered  that  no  matter  how  yielding  the  mass 
may  have  been,  it  is  also  sufficiently  resistant  to  have  prevented  the 
muscles  from  closing  to  their  utmost  limits.  It  is  therefore  necessary 
to  trim  these  surfaces  so  as  to  still  further  reduce  the  size  of  the  bulb, 
especially  at  the  posterior  end,  where  the  ridge  of  the  pharynx  is  ex- 
pected to  touch  it.  In  the  region  of  the  uvulae  the  sides  must  be 
trimmed  away  so  that  they  may  close  under  the  obturator,  and  to  this 
end  that  part  of  the  bulb  may  be  narrowed  at  the  lower  and  widened  at 
the  upper  side,  thus  producing  inclined  planes  against  which  the  leva- 
tors will  play  and  be  in  contact  at  all  times  during  their  contractions. 
In  the  region  of  the  uvulae  the  bulb  may  be  cut  away  on  a  line  with  the 
bases  of  the  uvulse,  so  that  the  surface  produced  will  be  a  plane  which 
if  extended  by  an  imaginary  line  would  reach  the  incisive  edges  of  the 
anterior  teeth. 

Figs.  981-983  are  introduced  to  show  the  great  variations  in  the  forms 
of  bulbs,  the  size  and  shape  being  dependent  upon  the  peculiarities  of 


Fig.  981. 


Fig.  982. 


Fig.  983. 


the  fissures  and  the  activity  of  the  throat  muscles.  In  Figs.  ^81  and 
983  a  indicates  the  flat  surface  where,  as  has  been  described,  the  bulb  is 
cut  away  near  the  bases  of  the  uvulse,  while  6,  b  show  the  slanting  sides 
against  which  the  levatores  play.  Fig.  982  shows  the  nasal  surface  of  a 
large  obturator,  and  along  the  centre  is  seen  the  depression,  which, 
experience  has  taught,  is  serviceable  in  many  cases  in  correcting  the 
nasal  quality  of  the  voice  usually  present.  Upon  the  upper  surface 
the  depression  alluded  to  is  seen  at  c,  but  it  must  be  borne  m  mind 

47 


738  PALATAL  MECHANISM. 

that  this  is  not  always  a  necessity,  being  less  so  in  small  obturators  (as 
in  Figs.  981  and  983)  than  in  large. 

The  model  having  been  brought  to  this  point,  plaster  is  mixed  as  for 
an  impression,  and  a  little  placed  upon  the  upper  side  of  the  plate,  ex- 
tended from  where  the  impression  material  ends  sufficiently  forward  to 
reach  the  anterior  end  of  the  fissure  when  placed  in  the  mouth.  The 
plate,  with  plaster  upon  it,  is  then  quickly  carried  into  place,  and  upon 
removal  the  plaster  will  have  taken  an  impression  of  the  forward  part 
of  the  cleft.  It  is  cut  away  to  a  level  with  the  upper  side  of  the  im- 
pression material,  and  with  it  completes  the  model  of  the  obturator, 
which  must  now  be  reproduced  in  hard  rubber. 

Plaster  moulds  are  next  made  in  which  to  reproduce  the  bulb  in  hard 
rubber,  and  when  flashed  and  ready  for  packing  the  bulb  is  made  as 
follows  :  Patterns  of  the  upper  and  under  surfaces  are  cut  from  thick 
tin-foil,  and  a  single  pattern  to  extend  around  the  sides  and  end. 
These  are  similarly  cut  from  sheet  rubber,  and  are  united  in  the  general 
form  of  the  bulb  by  placing  the  edges  together  and  pinching  them  fast 
with  a  pair  of  tweezers.  Before  finally  closing,  water  should  be  intro- 
duced, filling  the  bulb  about  three-quarters  full,  great  care  being  observed 
lest  the  edges  of  the  rubber  should  become  wet,  which  would  prevent 
perfect  union  and  allow  an  escape  of  steam  during  vulcanization,  the 
result  being  a  collapse  of  the  bulb.  If  these  steps  are  accurately  taken 
and  the  flask  tightly  closed,  the  bulb  will  be  thoroughly  well  filled  out 
and  will  be  a  perfect  reproduction  of  the  model. 

The  bulb  is  next  to  be  fitted  to  the  plate,  the  proper  position  being 
determined  by  models  which  were  taken  while  the  plate  and  wax  (im- 
pression material)  model  were  united.  A  hole  is  then  drilled  through 
the  bulb  and  plate,  through  which  an  iridio-platinum  bar  is  passed  and 
soldered  to  the  plate,  the  opposite  end  being  screw  cut  and  supplied  with 
a  nut.  The  hole  drilled  through  the  bulb  for  the  passage  of  the  bar  also 
serves  for  the  removal  of  the  water  used  in  vulcanizing.  The  surface 
of  the  plate  over  which  the  bulb  is  to  lie  is  smeared  with  gutta-percha, 
the  bulb  slipped  over  the  bar,  and  the  nut  turned  down  until  it  im- 
pinges. Then  by  warming  the  plate  over  a  Bunsen  burner  the  gutta- 
percha is  softened  and  the  nut  screwed  down,  driving  the  obturator  tight 
against  the  plate,  the  gutta-percha  serving  to  form  a  water-tight  joint. 
The  plate  and  bulb  are  then  polished  and  are  ready  for  the  patient. 


INDEX 


ABSCESS,  blind,  treatment  of,  595 
recurring,  595 
Absorption,  excessive,  of  alveolar  process, 

707 
Accessories  of  plaster  table,  21 
Acid  pan,  60 

solutions,  60 
Adhesions,  cicatricial,  274 

treatment  of,  274 
Alexander's  removable  bridge,  685 
Alloy  or  alloys,  82 
aluminum  bronze,  144 
and  mercury,  144 
with  zinc  and  tin,  144 
Bean's,  468 

for  cheioplastic  operation,  148 
copper  and  gold,  136 
and  nickel,  136 
and  platinum,  136 
and  silver,  136 
decomposition  of,  85 
density  of,  83 
table  of,  84 
ductility  of,  84 
fusibility  of,  85 
fusible,  149 
gold  for  clasps,  204 
and  copper,  108 
fineness,  102,  107 
and  mercury,  108 
and  palladium,  108 
plate,  tables  of,  103,  104 
and  platinum,  108 
and  silver,  109 
and  tin,  108 
and  zinc,  108 
influence  of  constituent  metals,  85 
Kingsley's,  468 
lead,  132 

and  gold,  133 
and  meicury,  132 
and  platinum,  133 
and  tin,  133 
table  of,  84 
liquation  of,  86 
malleability  of,  84 
with  mercury,  148 
preparation  of,  86 
properties  of,  82 

color,  84 
Reese,  148,  468 
temper   86 
tenacity,  84 
tin  and  gold,  148 


Alloy,  tin  and  lead,  149 
and  palladium,  149 
and  platinum,  148 
and  silver,  148 
and  gold,  148 
varieties  of,  83 
zinc  and  copper,  139 
and  gold,  139 
and  lead,  139 
and  mercury,  138 
and  platinum,  139 
and  silver,  139 
and  tin,  139 
Aluminum,  alloys,  144,  145 
annealing,  143 
bronze,  137 

solders  for,  144 
casting,  145 

Carroll's  method,  145 
plates  of,  475-478 
compounds  of,  147 
history  of  142 
methods  of  obtaining,  143 
its  occurrence,  141 

forms  of,  141 
plates,  146 

rubber  attachments,  523,  527 
I      reduction  of,  142 
steel,  129 

soldering,  146,  147 
uses  and  properties,  145 
Amalgam,  aluminum,  144 
copper,  134 

making,  135 
gold.  109 
tin,  148 
zinc,  138 
Anvil,  swaging,  19 

Arch,  maxillary,  effects  of  resorption,  407 
shape  of,  368 

upper  and  lower,  368 
Arrangement  of  full  cases,  406,  407 
Articulating  models,  353  et  seq. 
metal,  355 
mounting  models  in,  353 
full  cases,  353 
partial  cases,  354 
plaster,  352 
teeth,  382-384 
Walker,  375 
Articulation,  360 

for  rubber  dentures,  482 
Articulator,  351,  352 

anatomical,   Walker's,  376 

739 


740 


INDEX. 


Articulator,  anatomical,  Bonwill's,  376 
application  of,  380  et  seq. 
Bonwill's,  352,  353 
crown,  354 
S.  S.  White's,  351 
Artificial  crown,  preparation  for,  mechan- 
ical, 596 
by  excision  of  crown,  596 
by  tiles,  596,  697 
Ottolengui's  process,  597 
roots,  mechanical,  596 
sterilization  of  pulp-canals,  594 
therapeutics  of  pulp,  594 
teeth,  history  of,  210 

varieties  of,  210 
vela,  function  of,  715 
Assaying,  111 
Aurous  chlorides,  109 

BABBITT  metal,  149 
Fletcher's,  150 
Haskell's,  150 
Backing  stays,  411-415 

fitting,  Trueman's  method,  417 
forms  of,  414,  415 
for  irregular  surfaces,  412,  413 
patterns  for,  412 
Bailey's  moulding  flasks,  19 
Baking  continuous  gum,  460-462 
Bands,  clamp.  Angle's  adjustable,  166 
Farrar's,  166 
material  for,  1 69 
to  solder  together,  169 
Barrel  crowns,  589 
to  detach,  643 
preparing  teeth  for.  598 
to  repair,  543 
Bars  for  regulating  appliances,  154 
Bending  rubber  plates,  535,  536 
Bellows,  Burgess's,  41 

Fletcher's,  42 
Bench,  laboratory,  17 
Binary  temperaments,  tables  of,  582,  583 
Bites,  abnormal,  388 

direct  antagonism,  391 
protrusion  of  lower  jaw,  388 
of  upper  jaw, 390 
consequences  of  inaccurate,  257 
difficulties  in  taking,  355 

to  remedy,  355,  356 
plates  for  (How's),  357-360 
to  take,  347 
Black  on  sore  mouth,  708 
Blowpipe,  automatic,  48 
Downie's,  28 
Fletcher's,  31,  32 
gasoline,  47 
hand,  45 
hot  blast,  48,  49 
Lee's,  46 
Mellotte's,  45 
mouth,  43,  44 
oxy hydrogen,  Knapp's,  27 
Bonwill  crown,  620 
fitting  of,  620,  621 
for  molars,  622 
Ottolengui's  clamps,  621 


Bonwill  crown,  setting  of,  621-624 
Bows,  labial  and  lingual,  178-180 
for  regulating,  192-194 
for  regulating.  Angle's,  201,  202 
Case's,  197 
extrusion,  196 
Farrar's,  196,  200    ' 
in  protrusion,  194 
for  rotation,  194,  195 
Case's,  double,  197 
their  action,  199 
Brass  moulds  for  porcelain  teeth,  243 
Bridges  or  bridge,  dental,  648  et  seq. 
classes  of,  649,  650 
extension,  650,  681,  682 
plate,  691-693 

conditions  of  abutments,  692 
removable,  crowns  with,  692 
restoring  contour  by,  692,  693 
porcelain,  fitting  caps  to  abutments,  694 
setting  of,  697 

barrel  crowns,  697 
bars,  697,  698 
cement  for,  697 
filling  retaining  slots,  697,  698 
post  crowns,  697 
Bridge-work,  advantages  claimed  for,  650 
of  removable,  710 
anterior  bridge,  672 

with  post  and  collar  crowns,  673 
attaching  caps  to  facings,  664 
breakage  of,  698 

case  showing  indications  for,  679 
casting  bodies  of,  669,  670 
for  changing  bite,  679 

method  of  making,  679 
change  of  stress  by,  652 
combined  with  plate-work,  691-693 
constructing  parts,  661,  662 
definition  of,  648 
and  dental  diseases,  655 
aesthetic  requisites  of,  659 
to  detnch  fixed  forms,  698 
die-i)lates  i'or,  666,  667 
with  discontinuous  body,  679 
and  engineering  principles,  652,  653 
extensive,  adjusting  sections,  678 

soldering  of,  678 
faults  of,  654,  655 
filling  of  caps,  664 

dummies,  667 
fitting  facings  for  dummies,  663 
incisors,  673 
stays  to  incisors,  673 
fixed,  649 

to  form  occlusion,  663 
forming  incisor  dummies,  673 
with  four  abutments,  676,  677 
preparing  abutments,  677 
history,  648,  649 

HoUihgsworth's  method  of  forming  occlu- 
sion, 664 
hygienic  relation  of,  709,  710 

requisites  of,  659 
ill  effects  of,  710 
for  incisors,  671-675 
indication  for,  651 


INDEX. 


741 


Bridge-work,  limit  of,  682 

Litch's  method  of,  672 
making  bodies  of  bridges,  562 
manufacture  of,  661 

precautions,  661 
measuring  stress  upon,  653 
mechanical  aspect  of,  651 
Mellotte's,  671 

forming  collars  671,  672 
modes  of  attachment,  649,  650 
objections  against,  650 
porcelain,  693 

preparation  of  abutments,  656-659 
proper  forms  for  bars,  658 
reducing  abutments,  657 
removable,  649,  682-691 

Alexander's,  685 

choice  of,  683 

Curtis's,  686 

definition  of,  682 

objects  of,  682 

Eiiein's,  687-691 

construction  of,  689,  690 

Eiclimond's,  687 

sockets  for,  686 

Willis's,  684 

Winder's,  684,  685 
repair  of,  698 
repairing  of,  Bryant  on,  700,  701 

Darby  method,  700 

dummies,  699 

Mason's,  700 

post  abutments,  699 

splitting  crowns,  699 
requisites  of,  correct,  659 
rules  in  making,  654-656 
selection  of  variety,  660 
shaping  of  teeth,  656-659 

of  abutments,  reasons  for,  656,  657 

and  adjusting  bars,  677 

slots  in  abutments,  678 
for  bars,  658 

to  split  crowns,  698,  699 
stress  upon  abutments,  651-653 

anterior  bridge,  654 

pin  anchorages,  654 

pALCIUM  sulphate,  22 

\J  Callahan's  method  of  entering  canals, 

595 
Cap  and  bit,  203,  204 
Angle's,  204 
Goddard's,  203 
Mattheson's,  165 
occipital,  202 
Carroll's  method  of  casting  aluminum,  475- 

477 
Carving  block  teeth,  231  et  seq. 
Case's  double  bows,  197 
Cassius,  purple  of,  109,  221 
Cast  metal  dentures,  468 
base- plates  for,  469 

stiff,  for,  470 
beads  upon  palatal  surface,  469 
chamber  forms  (Chupein'sj,  468 
finishing,  473 
flasking,  471 


Cast  metal  dentures,  flasks  for,  471,  472 
fusing  alloy,  472 
gates  in  investment,  471 

in  Watt's  flask,  472 
grinding  gum  teeth,  470 
investment  for,  468 
luting  flask,  472 
pouring,  473 
repairs,  473 

requisites  of  alloys  for,  468 
to  solder,  473 
teeth  for  close  bites,  469 
plates,  aluminum,  475-478 
Bean's  method,  475 
Carroll's  method,  475-477 

crucible,  476 
gates  for,  476 
finishing,  477 
flasks  for,  476 
pouring,  477 
Carroll's  alloy,  477,  478 
clasps  for,  475 
vulcanite  attachments,  474 
plaster,  pouring  of,  299 

separating  from  impression,  300 
partial.  Case's,  301 
Cavities  in  teeth,  241 
Celluloid,  553 

alleged  deficiencies  of,  566 

cases   illustrating  artistic  features,    567- 

577 
composition  of,  555 
cooling  of  investments,  565 
dentures,  arranging  teeth,  562 
baking,  564 
base-plates  for,  561 
carving  wax  for,  562 
impression  for,  561 
investing,  563 
models  for,  561 
selection  of  teeth  for,  561,  562 
stippling  of,  563 
trimming  wax,  562 
vents  in  investments,  564 
history  of,  553,  554 
manufacture  of,  555 
moulding  of,  556,  565 

dry  heat  process.  Hunt's,  556 
glycerin  process,  566 
machines  for  "  Best,"  556,  557 
Camf)bell's,  558 
Evans',  558 
oil-bath  process,  556 
in  steam,  Alexander's,  556 
nature  of,  554 
physical  structure  of,  567 
properties  of,  555,  556 
to  remove  cases  from  flask,  565 
repairing  of,  565 
texture  of,  560 
teeth  for,  altering  forms,  468 
warping  of  plates,  567 
work,  plaster  for,  566 
models  for,  566 
Chamber  metal,  480 
Chambers,  vacuum,  303 
Cheioplastic  alloy,  148 


742 


INDEX. 


Chin  retractors,  205,  206 
Chlorides,  metallic,  87 
Choice  of  material  for  plate,  274 
Clasps,  337 
alloy,  104 

attached  to  plates,  341 
Bon  will's,  342 
bracing,  Essig's,  344 
broken  to  repair,  428 
upon  cast-metal  plates,  475 
fitting  of,  340 
forms  of,  338,  341,  342 
indications  for,  276 
making  of,  339 
partial,  341 
plates,  334  et  seq. 
on  rubber  plates,  514-516 
teeth,  273 

for  upper  dentures,  334  et  seq. 
uses  of,  337 

precautions,  338 
in  porcelain  teeth,  214 
Cleft  palate,  712 

acquired,  extent  of,  713 

artificial  vela  for,  715 

congenital  cases,  conditions  presenting, 

714 
education  of  patient,  720 

necessity  for,  720 
ill    efiects   of    surgical    measures,  713, 

714 
impressions  of,  728 
Kingsley's  velum  for,  716 

action  of,  717 
prognosis  of  congenital  cases,  713 

acquired  cases,  713 
varieties  of,  712 
vela  for  children,  720 
Coffin  split  plates,  164 
Collar  crowns,  609 
to  detach,  643 
to  fit  new  facing,  644 
fitting  barrel,  611 
forming  articulating  surface,  613 

band,  610 
Huey's   method   of    attaching   facings, 

617 
mandrels  for,  612 
measuring  root,  610 
with  molars,  616,  617 

porcelain  facings,  615-618 
for  bicuspids,  615 
and  post  crowns  for  bridge-work,  673 
with  post  in  roots,  616 
preparing  teeth  for,  610 
requisites  of,  610 
shaping  barrel,  611 
swaging  caps  for,  614 

Mellotte's  method,  614 
Color  frits,  216 

blue.  Hall's,  216 
gold  in,  216 
platinum  in,  216 
Wildman's,  217 
Colors  used  in  porcelain  teeth,  215 
(.'ombination  dentures,  521-529 
silver  and  rubber,  522 


Combination  enamels,  making  of,  218 

Hall's  formulae,  218,  219 
Continuous-gum    dentures,    advantages    of, 
446 
Allen's,  446 
arranging,  446,  453 
bites  for,  452 
Chemant,  446 
clicking  of,  447 

to  prevent,  447 
electric  furnace,  Custer's,  456 
enamelling,  461 
finishing,  462 
fitting  stays,  454 
forming  plate  for,  449 
care  in,  449,  450 
lower  plates,  450 
second  coating,  461 
forms  of  stays,  455 
fracture  of,  447 
to  avoid,  447 
enamel,  458 
furnace  fuel  for,  457 
fire-building,  458 
care  of,  458 
heel  to  plate,  450,  451 
impression  for,  448 
investing  for  soldering,  454 
mounting  teeth,  453 

upon  vulcanite,  464-466 
forming  block,  465 
objections  to,  447 
office  of  body,  458 

of  second  body,  461 
plates  for  soldering,  451 

testing  adaptation  of,  452 
remaking,  463 
repairing,  463 
setting  up  furnace,  457 
single  teeth  added  to,  464 
soldering,  455 
Tees  furnace,  456 
teeth  employed,  452 
treatment  of  models,  447-449 
vacuum  chamber,  448 
omission  of,  448 
when  employed,  447 
Copper,  133 
alloj's,  136 
amalgams,  134 
properties,  134 
reduction  from  ores,  134 
strips  with  Hollingsworth  system,  642 
tests  for,  137 
Cores  for  vulcanite  plates,  537,  538 
Corundum  wheels,  64 
Cotton  wedges  in  regulating,  175 
Counter-dies,  316 
metals  for,  312 
Crib,  Jackson,  185 

its  construction,  185,  186 
Crowns,  accidents  to,  643 
for  abraded  teeth,  618 
in  column,  618 
artificial,  anatomical  relations  of,  589 
classes,  588,  589 
collar  variety,  609 


INDEX. 


743 


Crowns,  artificial,  condition  of  enamel,  592 
detaching  barrel  crowns,  643 
forms  in  relation  to  stress,  591 
function  of  barrel,  590 

post,  590 
history  of,  588 

hygienic  relations  of,  709,  710 
over  vital  pulps,  591 
pathological  relations,  592 
of  pulp,  592 
of  dentine,  592 
pericementum,  592,  593 
physiological  condition  of  dentine,  592 
of  pericementum,  592 
relations  of,  591 
post  and  plate,  606 
support,  588,  589 
preparation  of  roots  for,  593-601 

teeth,  therapeutic,  593 
relations  to  stress,  590 
requisites  of,  602 
selection  of  type,  603 
what  constitutes,  588 
barrel,  598 

preparing  teeth  for,  Case,  599 
How,  600 
Starr,  600 
Bonwill,  620 
Brown,  632 

cervical  outlines  of,  601,  602 
to  detach,  when  set  with  gutta-percha, 

644 
Downie,  622 
Gates-Bonwill,  623 

use  of  screws  with,  623 
Hoi  lings  worth  system,  636 
Logan,  623-631 
Mason's  detachable,  619,  620 
partial,  603-606 

incisors,  603,  604 
shells,  605,  606 
for  molars,  605 
for  incisors,  606 
porcelain  faced  for  vital  teeth,  618 
post  and  collar,  619 
ready-made,  620 
removable,  634-636 
with  removable  pins,  636 
repairing  of,  643,  644 
restoring  root-forms  for,  600,  601 
retaining  media  for,  645 
Richmond,  619 
Crucibles,  35 
Custer  electric  furnace,  456,  458 

method  of  fusing  platinum,  29,  30 
Curtis  removable  bridge,  686,  687 

sockets  for  bridge-work,  686,  687 
Cusp  crowns  for  molars,  617 

DENTIMETER,  Kirk's,  611 
Dentures  of  all  porcelain,  255,  256 
artificial  cleansing  of,  705,  711 
acid  mouths,  705 
care  in,  711 
clasps,  effects  of,  703-705 
evil  effects  of,  702  et  seq. 
functions  of,  702 


Dentures,     artificial,     hygienic     conditions 
aflected  by  materials,  702 
effects  of  spiral  springs,  703 

of  bases,  705,  706 
relations  of,  702  et  seq. 
requisites  of  clasps,  703-705 
ill  effects  of  uncleanliness,  706 
means  of  retention,  hygienic  effects,  703 
to  prevent  irritation  by,  711 
wearmg  at  night,  704,  705 
upon  celluloid  without  anterior  gum,  573 
changes  effected  by  altering  arrange- 
ment, 568 
effects  of  spacing  teeth,  575 

of  omitting,  575,  576 
for  elderly  persons,  568-570 
illustrating  artistic  features,  567-577 
imitation  of  irregularities,  576,  577 
with  spiral  springs,  574,  575 
for  young  adult,  578 
combination,  521-529 
partial,  392 

use  of  gum  teeth,  392 
plain  teeth,  393,  394 
plate  teeth,  393,  394 
temporary,  387,  388 
trial  of,  in  mouth,  408 
type  selected,  276 

conditions  governing,  276 
Dies,  309 

advantages  of  zinc,  310 
for  bridge-work,  662,  663 
counter-;  139,  312,  316 
and  counter-die  metals,  care  of,  23 
making  by  dipping,  318 
of  fusible  alloys,  318 
metals.  Babbitt's,  311 

requisites,  properties  of,  310 
Spence's,  311 

use  of,  311,  312 
used,  310,  31 1 
zinc,  Bertiia,  311 
plates  for  forming  caps,  666,  667 
pouring,  316 

Babbitt  metal,  316 
zinc,  316 
separating  from  counter-die,  318 
Dinitro-cellulin,  554 
Downie's  crown,  making,  262 

furnace,  uses  of,  262,  263 
Drag  screw,  183 

Angle's  method  of  using,  184 
Goddard's  methods  of  using,  184 
Draw-plate,  38 
Drawing  wire,  157 

EBONITE,  479 
plate  with  pink  rim,  513 
flasking,  513 
Electric  furnace,  29,  264 

to  fuse  platinum  by,  265 
Electro-deposit  plate,  345 
Electrolysis,  reduction  of  metallic  salts  by, 

93 
Enamels  for  continuous-gum  work,  223 
Allen's,  224 
Hall's,  219 


^44 


INDEX. 


Enamels   for  continuous-gum   vrork.   Hun- 
ter's, 223 
Moffeii's,  223 
Smith's  223 
Wildman's.  217 

their  application.  220 
Enamelling  continuous  gum,  462 
English  teeth,  26-5 

Eruption,  appliances  for  forcible.  182 
Essig's  clasp  for  lower  dentures.  344 

method  of  mounting  natural  teeth,  429, 
516,  517 
of  repairing  bv  riveting,  429 
Evans  celluloid  machine,  5oS.  559 

use  of,  559,  560 
Expansion  of  arch,  appliances  for.  1S9-190 
Extension  bridges,  6*1,  682 

Parr's.  682 
Extruded  teeth,  appliances  for,  181 
for  construction  of,  ISl 

FACIXGS  for  bridge-work.  662.  663 
Feldspar  in  porcelain  teeth,  212 
Files  for  plate  work.  413 

rubber  work,  510 
Finishing  palatal  surfaces  of  metal  plates,  421 
soldered  dentures.  419 

means  employed.  419,  420 
Flasking  cases  for  rubber  dentures,  491 
Flasks  for  anificiai  vela.  733.  734 
Brown,  491 

for  cast-metal  dentures.  471.  472 
for  celluloid  work,  560 
Griswold.  489 
Hayes,  491 
moulding.  19 
Bailev%.  313 
Hawe's,  313 
for  rubber  work,  488-491 
Seabury,  494 
Star.  488 

Whitney,  4S9,  490 
Flexible  rims,  539 
Fluorides,  88 
Forces  applied  in  regulating  teeth,  171 

received  by  teeth.  376—379 
Forcible  eruption  of  teeth,  182,  183 
Formulas  for  continuous-gum  body,  467 

enamel,  467 
Fracmred  jaw,  impression  of  296 
Furnaces  for  baking  porcelain  teeth,  258 
Downie's.  261 
Land's.  259 
Verrier's,  260 
carbon,  26 
electric.  29 

Custer's.  264 
gas.  Downie.  .35 

Fletcher.  24,  32,  34 
gasoline,  25 
muffles.  Meyer's.  263 
Fusible  alloys.  149 
Mellottes.  149 
Eichmond's,  149 

/"lAERETSON'S  bite-guide.  355 
Ijr  Gasoline  furnace,  Geofrorers.  25 


Gauge.  Brown  and  Sharpe,  154 
Gauge-plate,  38 
Gear's  shaded  rubber,  535 
,  Genese  crown,  635 
1  German  silver,  136 

-  Girdwood's     method     of    banding    Logan 
I  crowns.  630 

i  Gold.  93 

'      alloys  of  102-108 
tsoldei-s).  105,  106 
analysis  of  native,  94 
assays  of  110 

by  scorification.  111 
brittle,  treatment  of  98 
chemically  pure,  preparation  of,  99 

for  clasps,  207.  404 
compounds  of,  108 
chlorides.  108.  109 
with  chlorine.  108.  109 
discrimination  of,  110 
extreme  tenuity,  94  .    _ 

I      fulminating,  110 

methods  of  obtaining.  95.  96 
iiy  amalgamation.  96 
by  washing,  95 
native  forms  of,  95 
occurrence  and  distribution.  93 
precipitation  of  from  solution,  100-102 
properties  of.  93.  94 
recovery  of.  from  sweeping,  112 
reducing  fineness  of,  106 
refining.  96.  97 
by  chlorine.  98 
nitric- acid  process.  97 
quartation  process.  96 
sulphuric-acid  process,  97 
shredded.  101 
silicate  of  217 

making  of  217 
and  sodium  hyposulphite  (^sel  d'orj,  109 
tests  for.  110  " 
volatility  of,  94 
Grinding  blocks,  405 

full  c-ases  plate  teeth,  406,  407 
teeth.  402-405 
gum.  402.  403 
Gum  frit.  221 

making  of,  221.  222 
Gums,  natural  structure  of,  270 
m'  rbid  conditions,  270,  271 
to  remove  from  root  faces,  595,  596 
spongy,  272 
wash  for.  272 
Gntta-percha  heater.  How's,  647 

indications  for  using  to  set  crowns,  645 
setting  crowns  with,  646,  647 

HEATEE  for  rubber,  496 
Hippocrates  on  temperament,  578 
Hollingsworth   method  of  banding  Logan 
crowns,  631 
of  casting  bridges,  669,  670 
of  making  dummy  caps,  665 
system  of  copper  strips,  642 
of  crowning,  636—643 
of  forming  dies,  638,  639 
solid  cusps,  640 


IXDEX. 


745 


Hollingsworth  system  of  gold  crowns,  638 
et  seq. 

%for  incisors,  640,  641 
inserting  porcelain  facings,  641,  642 
Hooks,  application  of,  176 

for  regulating  appliances,  167 
How's  gutta-percha  heater,  647 
Huey's  method  of  attaching  porcelain   to 

collar  crowns,  617 
Hypertrophied  gum,  to  remove  from  root 
faces,  595,  596 

TMPEESSIONS  of  cleft  palate,  728 
X     fusible  metal  casts  of,  296 
of  irritable  palate,  2S8 
materials  employed,  277 
beeswax,  277 

mixtures  of,  278 
plaster  of  Paris,  277 
for  obturator.  736 

partial  dentures,  289-295 
in  plaster,  taking  of,  285  et  seq. 
preparation  of  patient,  286 
selection  of  material,  284 

plaster,  284 
taking,  for  fractured  jaw,  296 
in  heat-softened  materials,  285 
loose  teeth.  295 
palatal  defects,  296 
trays,  278 

altering  forms  of,  282 

for  special  cases,  292-294 
Bean"s  method  of  making,  284 
Catchings,  289 
for  lower  jaw,  279 
office  of,  278 

partial  lower  cases,  280,  281 
upper  cases,  280 
adjustable,  280 
for  special  cases,  283 
treatment  of,  for  casting,  297 
Incisors,  partial  crowns  for,  603,  604 
of  gold.  604 
of  porcelain,  605 
Ingot  moulds.  36 
Interdental  splints,  547 
Investing  dentures,  415 
Investment  material,  415 
Iodides.  88 
Iron,  alloys,  new.  129 

to  distinguish  from  steel,  132 
distribution,  127 
malleable.  132 
properties  of.  127 
Irritable  palate  in  impression-taking.  288 

JACK'S  regulating  plate,  flasking  for.  547 
for  retaining.  546 
for  traction,  546 
Jack-screws.  Angle's,  171 
application  of.  173 
Farrar"s,  171.  172 
Jacque.  definition  of  temperament,  578 

table  of  temperaments.  581 
Joints  between  gum-blocks.  386 
discolored  in  rubber  work,  486 
to  prevent  ingress  of  rubber  into,  496 


KAOLIX  in  porcelain  teeth,  214 
Key-making,  161 
Kingslev's  slotted  regulating  plate,  545 

velum,  715,  716 
Kirk  on  sore  mouth,  709 
Kirk's  dentimeter,  611 

method  of  fitting  Logan  crowns,  625 
Knapp's  blowpipe,  27 

LABOEATOEY  workbench,  17 
accessories  of,  18 
Ladle-melting,  24 
Lamp,  alcohol,  50,  51 
I  Lathes,  61-64 

accessories,  61—68 
chucks,  62 

corundum  wheels,  64 
Lead,  alloys,  132 

reduction  of,  132 
Ligatures  in  regulating,  175 
silk,  175 
wire,  176 
Lining,  Vulcan,  529 

vulcanite  plates,  529,  530 
Lip  line,  351 
Liquid  silex  with  rubber  dentures,  use  of, 

497 
Litch's  pin  attachment,  672 
Local  effects  of  artificial  dentures,  702,  703 
Logan  crown,  623-631 
to  band,  629-631 
fitting  of,  without  model,  625 

Kirk's  method,  625 
selection  and  fitting  of,  624-631 
to  set  with  gutta-percha,  629 

zinc  phosphate,  628 
"White's  method  of  attaching  porcelain, 
627 
of  fitting,  626,  627 
Lower  jaw,  articulation  of,  346 
movements  of,  346,  375 
plates,  329 

MAXDEELS  for  shaping  barrels,  612 
Mason's  detachable  crown,  619,  620 
Matrices  for  forming  blocks,  242 

brass,  243 
Maxillary  arches  after  resorption,  407 
Mellotte's  bulkhead  bridge.  671 
Melting  metals,  appliances  empiloyed.  22-35 
by  electric  current  i  Custer  ),  29.  30 
modes  of,  24 
Metals,  agents  which  volatilize,  82 
conduction  of  electricity,  79 

of  heat,  78 
crystallization  of,  81 
ductility  of,  79 

employed  in  metallic  condition,  75 
expansion,  77,  78 

(alloys),  78 
fusiug-points  of,  76,  77 
gauge.  154 
ingot.  153 
malleability  oi,  79 
noble.  75 
plate,  153 
properties  of,  75-82 


746 


INDEX. 


Metals,  properties  of,  color,  76 
lustre,  76 
odor,,  76 
taste,  76 
reduction  of,  90 
for  regulating  appliances,  154 
specific  heat  of,  77 
table  of,  74,  75 
tenacity  of,  80 
volatility  of,  81 
Meyer's  mnfiles,  263 
Mills,  rolling,  37 
Models  for  celluloid  work,  566 
plaster,  trimming  of,  301 

waxing  to  prevent  bruising,  302,  303 
preparation  of,  for  moulding,  307 
waxing  for  rim,  308 
to  prevent  pressure,  308 
Mono-nitro-cellulin,  554 
Moulding  box,  18 
accessories  of,  19 
celluloid,  565 

conditions  complicating,  314 
cores  in,  315 
flasks,  Bailey's,  19,  313 

Hawes',  313 
process  of,  313  et  seq. 
Moulds,  ingot,  36 

NATUEAL  teeth  to  mount  on  plates,  516, 
517,429 
Nut-making,  160 

OBTUEATOR  to  attach  to  plates,  738 
attached  to  plate,  721 
construction  of,  736 
forming  model  for,  736 

patterns  for,  738 
function  of,  722 
with  hinge,  722 
impressions  for,  731,  736 
indications  for  use  of  hinge,  723 
ineffectiveness  of  hinge,  722 
making  plate,  736 
mode  of  attaching  to  plate,  721 

of  investing,  738 

of  packing  rubber,  738 
pattern  for,  737 
requisites  of,  720,  721 
Schnltsky's,  724,  725 
shapes  of,  737 
Suersen's,  722 
for  syphilitic  lesion,  538 
value  of  natural  teeth  for  retention  of,  736 
with  velum,  718 

making  of,  for  special  case,  718,  719 
Occipital  cap,  202 
Occlusion,  346  et  seq. 
balance  of,  372 
Bonwill  on,  370  et  seq. 
complete,  346 
curvature  of,  372 
movements  of,  347 
normal,  369-371 
obtaining,  347-349 
overbite,  371 
wax  blocks,  350 


Occlusion,  wax  blocks,  trimming  of,  351 
Ottolengui's  root-clamps,  621 

root  facers,  597 
Oxides,  reduction  of,  88,  89 
Oxyphosphate,  setting  crowns  with,  645,  646 

PALATAL  defects,  impression  for,  296 
Palate,  cleft,  712-738 
Parallel  pliers,  414 
Parr's  extension  bridge,  682 

sockets  for  bridge-work,  686 
Partial  cases,  vulcanite,  514,  518 
dentures,  arranging  teeth,  392 
lower  plates,  330-333 
Patterns,  forming  of,  321 
Pickling,  forming,  60 
Pin  punch,  413 

splitter,  413 
Pink  rubber  on  soldered  dentures,  540 

investing,  541 
Plaster  cast,  pouring  of,  299 

for  casting,  requisite  properties  of,  298 

for  impressions,  23,  284 

for  models,  23 

of  Paris,  22 

rules  for  using,  284,  285 

table,  20 

accessories  of,  21 
Plates,  articulating  wax,  348 
attaching  chamber  piece  to,  325 
bridges,  691-693 
clasp,  334  et  seq. 

making  of,  336,  337 
configuration  of  palatal  surface,  396 

effects  of,  395,  396 
draw-,  38 

electro-deposit,  345 
files,  413 

forming  chamber  cap,  324 
cutting  out,  324 
upon  die,  322 
malleting,  323 
pattern  for,  321 
gauge,  38 
lower,  329 

making  of,  329,  330 
partial,  330-333 
classes  of,  331 
forming  upon  die.  333 
models  for,  332 
strengthening  pieces  foi",  333 
uniting  sections,  330 
metal,  indications  for,  274 
metallic,  indications  for,  320 
metals,  properties  of,  320 
outline,  marking  of,  301 

full  upper  cases,  301,  302 

lower  cases,  302 
partial  lower  cases,  302 
for  regulating,  162,  163 

Coffin,  164 
to  rim,  408-410 
strengtiiening  pieces  for,  328 
swaged  metals  for,  319 
swaging  aluminum,  326 
of  partial,  326  et  seq. 
rim,  325 


INDEX. 


14:1 


Plates,  swaging,  without  cut-out   chamber, 
326 
testing  adaptation  of,  324 
thickness  of  metals  used,  322 
vacuum  chamber,  275 

lateral,  275 
vulcanite,  indications  for,  275 
wiring,  410,  411 
Platinum,  121 
alloys,  125 
black,  125 

chemical  properties,  125 
chloride,  126 
discrimination  of,  127 
effects  of,  upon  tissues,  704 
to  fuse,  265 

fusing  of,  by  electricity,  29,  30 
fusion  of,  124 
and   gold  frits,  making,  Hall's   method, 

216 
impurities,  124 
oxides,  126 
properties,  124 
reduction  from  ores,  122 
separation  of,  123 
solder  for,  126 
solvent  of,  125 
spongy,  127 
sulphides,  127 
welding,  123 
Plumpers  for  vulcanite  plates,  537 
Polishing  soldered  dentures,  420 
Porcelain  body  for  continuous  gum,  458,  467 
first  coat,  458,  459 
forming,  459 
fusing,  460 
bridge-baking,  695 

fitting  caps  to  abutments,  694 
stay  and  bar,  594 
teeth,  694-696 
incisors,  69.6 

upon  bicuspids  and  molars,  696 
incisors,  695 
plates,  695,  696 
with  post  crown,  696 
for  restoring  contour,  695,  696 
work,  693 
dentures,  254 
teeth,  bodies  of,  211 
burning,  257,  258 
enamels  of,  212 
history  of,  210 

materials  used  in  making,  211 
Posts  for  artificial  ci'owns,  size  of,  606 
and  collar  crown,  589 
crowns,  588,  589 
and  plate  crown,  607 
backing,  609 
fitting  tooth,  609 
finishing,  609 
making  of,  607-609 
preparing  base,  608 
soldering,  609 
shaping  root,  607 
swaging  plate,  607 
Powders,  finishing,  67 
Precious  metals,  care  of,  240 


Protrusion  of  lower  jaw,  388 

of  upper  jaw,  390 
Pulps,  to  devitalize,  593,  594 
Purple  of  Cassius,  109,  221 
preparation  of,  109 

Wildraan's  methods,  109 

/QUARTZ  in  porcelain  teeth,  213 

REDUCING  fineness  of  gold,  106 
teeth  for  barrel  crowns,  598 
Reduction  of  metallic  chlorides,  91 
of  metals,  90 
sulphides,  91 
oxides,  92 

salts  by  electrolysis,  93 
Regulating  appliances,  bars  for,  154 
Coffin's,  541-543 

to  form  wires,  542,  543 
nuts  for,  155,  170 
rubber,  541  et  seq. 

retaining,  features  of,  544 
screws,  retaining,  155 
swaged  caps  for,  155 
tools  required  in  making,  155 
tubes  for,  154,  170 
wire  for,  154,  170 
piano,  for,  155 
plates,  rubber,  for  protruding  teeth,  544 
for  rotating  teeth,  545 
Kingsley's  slotted,  545 
for  traction.  Jack's,  546 
teeth,  forces  applied,  171 
Removable  bridges,  682-691 
bridge-work,  Cnrtis's,  686 
Rhein's,  687-691 
crowns  for,  689 
sockets  for,  690,  691 
Richmond's,  687 
crowns,  634-636 
Repairing  bridge-work.  698 
cast-metal  dentures,  473 
celluloid,  565 
crowns,  643 
facings,  collar  crowns,  644 

post  and  plate  crown,  644 
soldered  dentures,  424 
adding  tooth,  427 
clasps,  428 
cracks,  427 

faulty  adaptation,  425 
modus  operandi  of,  425 
patches,  426 
remaking,  425 
resorption  necessitating,  425 
■  riveting,  427 
riveting,  Essig's  method,  429 
using  old  tooth,  428 
vulcanite  plates,  518-521 
Retaining  appliances,  207 
bands,  207,  208^ 
and  wires,  207 
plates,  209 

twisted  wires  (Case's),  208 
media  for  artificial  crowns,  645 
plates,  rubber,  544 


748 


INDEX. 


Retractor,  chin,  205,  206 

Ribbons,  metallic,  for  regulating  appliances, 

165 
Eichmond  crowns,  619 
attaching  cap,  619 

to  post,  619 
fitting  band,  619 
Richmond's  new  crown,  632-634 
fitting  crown,  633 
precautions,  634 
setting,  633 
shaping  tooth  for,  632 
uses  of,  634 
removable  bridge,  687 
crown,  635 
Rimming  plates,  408-410 
Rims,  flexible,  539 

for  vulcanite  attachments,  523-526 
Rolling  mill,  37 
Root  forms,  restoring,  600,  601 
Roots,  neck  sections  of,  599 

of  teeth,  mechanical  function  of,  589,  590 
stress  upon,  589,  590 
Rotation,  double,  178 
by  hooks,  177 
sockets  and  level's  for,  179 
Rubber,  or  caoutchouc,  479 
attachments,  522-529 
dentures,  articulation  for,  482 
models,  483 
points  observed,  483 
base-plates  for,  481 

gutta-percha,  481 
black  with  pink  rim,  513 
buffing,  512        ^ 
carving  wax,  487 
casts  for,  480 

cause  of  discolored  joints,  486 
clasps,  514-516 
finishing,  509 
files  for,  510 
flasking,  491 

cases  without  i-ims,  475 
undercut  cases,  494 
flasks  for,  488-491 
flexible  rims,  539 
gauging  quantity  of  rubber,  498 
by  weight,  498 
rubber  for  pink  rim,  499 
heater,  496 
partial,  514r-518 
lower,  515 
bars  in,  516 
gold  in,  515 
pink  rubber  rim,  484 
plate  teeth  on,  514 
polishing,  512 
presses  for,  500 

to  prevent  discolored  joints,  486,  496 
removing  wax  from  matrix,  492 
repairing,  518-521 
scraping,  511 
smoothing,  511 
softening  rubber,  499 
teeth  in,  484.     See  Plate  on  p.  485. 

advantages  of  single,  484 
tin-foil  in  matrix,  497 


Rubber  dentures,  use  of  liquid  silex,  497 
vacuum  chamber,  481 

omission  of,  481 
vents  for  surplus  rubber,  492,  493 
vulcanizers,  500-504 
wax  carvers,  486 
waxing  cases,  487 
effects  of,  as  base,  706,  707 

causes  of,  707 
hard,  479 
impurities  of,  479 
origin  of,  479 

plates,  absence  of  free  mercury  in,  708 
beading,  535,  536 
fracture  of,  518,  519 
hvgienic  reasons  for  perfect  vulcanizing, 
708 
sore  mouth,  706 
tubing  for  regulating,  174 

bands  made  of,  174 
vulcanizable  composition  of,  480' 

dentures  upon,  480 
wedges  in  regulating,  175 
Rules  for  soldering,  418 

SAND  for  moulding,  309 
preparation  of,  309,  310 
Schultsky's  obturator,  724,  725 

its  value  as  compared  with  velum,  725 
Scrapers,  Kingsley's,  512 
Selecting  teeth,  398 
Separating  media,  21,  22,  299 
collodion,  297 
soapsuds,  297 
varnishes,  298 
Sercombe's  velum,  727 
Shapes  of  teeth,  224 
Sheet  metal  or  plate,  153 
Shot,  swaging  with,  344,  345 
Silex,  liquid,  497 
Silica  in  porcelain  teeth,  213 
Silver,  alloys,  119,  TiO 
compounds  of,  117 
discrimination  of,  117 
dry  process,  118 
wet  process,  118 
electro-deposit  of,  121 
German,  136 

hygienic  effects  of,  702,  704 
its  occurrence  and  distribution,  113 
properties  of,  113 
pure,  118 

obtaining,  119 
precipitation  of,  119 
reduction  of,  115, 116 
separation  from  ores,  114,  115 
solders,  120,  121 
whitening  of,  121 
Sockets  for  removable  bridges.  Parr's,  686 
Sodium  silicate,  497 
Soft  gums,  272 
solders,  133 
Solder  silver,  120,  121 
Soldering  cast-metal  dentures,  473 
accessories,  39,  40,  56-59 
clamps,  58 
Mellotte's,  58,  59 


INDEX. 


749 


Soldering,  accessories,  tweezers,  56,  57 
apparatus,  39 
furnaces,  54,  55 
precautions,  39 
rules  for,  418 
stays  to  plate,  419 
supports,  51-55 

carbon  basins,  52,  53 
charcoal,  51 

graphite  and  fire-clay,  52 
tables,  40 
Bishop's,  41 
Solders,  82 
gold,  105,  106 
soft,  133 
Speech,  mechanism  of,  715 
Speyer's  adhesion  forms,  530 

plates,  530 
Spiral  springs,  421  et  seq. 
arms  for,  424 
with  celluloid,  574,  575 
making  of,  422,  423 
Splints,  interdental,  articulation  for,  548 
Bean's,  547 
Gunning's,  547 
impressions  for,  547,  548 
Kingsley's,  551,  552 
models  for,  548 
packing  rubber  for,  550 
investing  for,  550 
waxing  for,  549 
Split  plate.  Coffin's,  its  uses,  187,  188 

Goddard's  modification,  188 
Spring,  Matteson's,  174 

Talbot's,  173 
Springs,  spiral,  421  et  seq. 
Spiirzheim  on  temperament,  579 
Staining  porcelain  teeth,  268,  269 

teeth,  240,  241 
Starr's  removable  bridge,  683,  684 
Stays,  backing,  411-415 
for  bridge-work,  673 
Steel,  128 

aluminum,  129 

Bessemer,  129 

case-hardening,  132  < 

chrome,  130 

copper,  130 

hardening  and  tempering,  131 

temperatures  of,  131 
making  of,  129 
manganese,  130 
nickel,  130 
Stippling  wax,  celluloid  dentures,  563 
Stomatitis,  treatment  of,  271 
Suersen's  obturator,  722 
Sulphides,  90 
Swaging  anvil,  19 
block,  19 

with  shot  (Parker),  344,  345 
Syphilitic  lesion,  538 

obturator,  denture  for,  538 

TABLE,  plaster,  20 
soldering,  40 
of  temperatures  and   pressures  of  steam, 
507 


Tables  of  temperaments,  580-587 
Taps  and  dies,  158 

Teeth,  actual  and  relative  sizes  of,  226,  227 
adapting  to  plate,  402,  403 
alteration  of  forms  of  porcelain,  228 
anatomy  of,  362,  363 
arrangement  of,  229,  230,  401 

ethnological  features  in,  230 
artificial  classes  of,  364 

their  application,  365  et  seq. 
blocks,  bisciiiting,  237 
carving  guide-walls,  282 
instruments  used,  234,  235 
mixing  body  for,  233 
moulding,  236 
trimming,  237 
enamelling,  238,  239 
errors  in  baking,  240 
fitting  sections  of  moulds,  251,  252 
forming  matrices,  242 

plaster  moulds,  247,  248 
making  brass  moulds,  248,  249 
foundation  plate,  245 
frame,  246 
moulding  in  brass  moulds,  252,  253 
moulds  for  special  cases,  253,  254 
plaster  blanks  for,  243,  244 

moulds,  245 
precautions  in  baking,  240 
staining,  240,  241 
trimming  brass  moulds,  250 
unusual  forms,  567 
carving  of  blocks,  231  et  seq. 
clasp,  273 
for  continuous-gum  work,  267 

Land's,  267 
countersink,  266 
English,  265 
extraction  of,  271,  272 

discrimination  in,  272 
forms  in  temperaments,  225 
geometrical  arrangement  of,  373,  374 

Walker's,  376 
grinding  of,  402 
jointing  of,  402 

natural,  to  utilize  in  prosthesis,  273 
j)inless  blocks,  265 
positions  of  ai-tificial,  401,  402 
selection  of,  398  et  seq. 

of  gum,  398 
shapes  of,  224 
sizes  of,  224 
staining,  268 
surfaces  of,  361 

occluding,  362 
tinting,  268 
unusual  shapes,  228 
Temperamental  characteristics  of  the  teeth, 

table  of,  584,  586,^587 
Temperaments,  analysis  of,  578 
the  balanced,  578 
bilious  (Spurzheim),  579 
binary,  585 

cause  of  (Hippocrates),  578 
choleric  (Hippocrates),  578 
definition  of,  578 
by  Hippocrates,  578 


750 


INDEX. 


Temperaments,  Jacque's  classification,  579 
J.  W.  White  on,  585 
lymphatic  (Spurzheim),  579 
melancholic  (Hippocrates),  578 
mental  (Hippocrates),  579 
motive  (Jacque),  579 
nervous  (Gregory),  579 

(Spurzheim),  579 
pathological,  579 
phlegmatic  (Hippocrates),  578 
sanguine  (Hippocrates),  578 

(Spurzheim),  579 
Spurzheim  on,  579 
table  of  binary  compounds,  582,  583 
for  the  diagnosis  of,  580 
illustrating  dental  relations,  584 
of  Jacque's    anatomical    classification, 

581 
vital,  579 
Temperamentum,  temperatum,  578 
Temporary  dentures,  387,  388 
Temporo-maxillary  articulation,  exact  move- 
ment of,  376 
Thread-cutting,  159 
Tin  chlorides,  151 
detection  of,  152 

foil  with  rubber  dentures,  use  of,  497 
history  and  properties,  148 
obtaining  pure,  150 
solvents  of,  151 

in  the  vulcanizing  process,  151 
for  weighting  dentures,  151 
Tools,  bench,  71-73 

care  of,  73 
Tooth  bodies,  214 
formulae  for,  214 
Hall's,  215 
Wildman's,  215 
Townsend's    method     of    banding     Logan 

crowns,  629,  630 
Traction  apparatus  with  tubes  and  bands,  179 

by  hooks,  177 
Trays,  impression,  for  lower  jaw,  279 
Treatment  of  impression  for  casting,  297 
Tri-nitro-cellulin,  554 
Tube  teeth,  430 

alloys  for  posts,  444 
attaching  to  plate,  435 
for  bridge-work,  439 

making  bridges,  440 
base  for,  441 
clasps  for,  442 
(fixed),  442-445 
construction  of,  430 
for  crown  replacement,  436 
crowns  upon  living  teeth,  438 
as  crowns,  436-438 

posts  for,  436 
fitting  posts  for,  433 
fixation  with  zinc  phosphate,  445 
Girdwood,  430,  434 
grinding,  434 
with  gums,  435 
to  hide  posts,  445 
over  metallic  root-caps,  438 
on  partial  cases,  435 
on  plates,  432  et  seq. 


Tube  teeth,  soldering  posts  for,  433 
tools  used  in  mounting,  431,  432 
uses  of,  430,  431 
Tubes,  application  of,  176 

for  regulating  appliances,  154 
as  sockets,  180,  181 
to  solder  to  band,  168 
their  uses  in  regulating,  178 
upon  traction  apparatus,  180 
Tubing,  making   of,  for  regulating   appli- 
ances, 158 

TTNDEECUT  ridges,  to  flask,  494 

VACUUM  chambers,  303 
horseshoe,  306 
lateral,  307 
position  of,  304,  305 

conditions  governing,  306,  307 
Vela,  artificial  function  of,  715 
correction  of  models  for,  732 
flasks  for  investing,  733,  734 
impressions  for,  728,  729 

for,  causes  of  inaccuracy,  729 
foi',  parts  embraced  in,  730,  731 
of  nasal  cavity,  731 
investing  in  flask,  733,  734 

metal  moulds,  734 
making  of,  732 
models  of,  732,  733 
of  fitting,  733 
for  plaster,  728 
moulding  metal  forms  for,  734 
packing  rubber  in  moulds,  735 
trial  plates  for,  732 
vulcanizing,  736 
Velum,  artificial,  Kingsley's,  715 
choice  of,  for  children,  720 
with  hinged  extension,  726,  728 
mode  of  arranging  with  hinge,  727,  728 
with  obturator,  718 
Sercombe's,  727 
Vulcanite  attachments,  522-529 
aluminum  not  suited  for,  523 
cleats  for,  524 
on  fusible  alloy,  522 
Vulcanizable  rubber,  479 
Vulcanizers,  Davis's,  501 
escape  of  steam  from,  508 
explosion  of,  508 
gas  regulators  for,  504-506 
Hayes's,  500 
Lewis's,  501,  502 
pressure  in,  507 
Seabury's,  503,  504 
thermometers,  507 

broken  mercury  column,  507 
mercury  bath  for,  508 
scales  for,  508 
time  regulators  for,  505,  506 
rule  for  setting,  505 
Vulcanizing  process,  509 
on  tin,  151 

WALKER'S  discovery  in  regional  anat- 
omy, 376 


INDEX. 


751 


Walker's  granular  gum,  534 
Wax,  adhesive,  69 
fluxed,  69 
spatula,  70 

heater,  71 
Wedges  in  regulating,  wood,  174 

cotton,  175 

rubber,  175 
Weighted  rubber,  536 

use  of,  536,  537 
Wheels,  corundum,  64 

brush,  66,  67 
White,  J.  W.,  on  temperaments,  585 
White's  method  of  fitting   Logan   crowns, 

626,  627 
Williams'  bridge,  680 

construction  of,  681 
Willis'  removable  bridge,  684 
Winder's  removable  bridge,  684,  685 
Wire,  pinched  in  regulating,  176 


Wire  for  regulating  appliances,  134 

to  solder  to  band,  168 
Wire-drawing,  157 
Wiring  plates.  410,  411 
Wood  compressed  in  regulating,  174 
Wunsche's  plates,  531 

application  of,  532,  533 

ZINC,  alloys  of,  138 
antiquity  of,  138 
compounds  of,  141 
counter-dies,  140 

uses  of,  140 
dies,  139 
ores  of,  138 
properties  of,  138 

phosphate,    setting     crowns    with,     645, 
646 
Zylonite,  553,  555 
advantages  over  celluloid,  577 


Date  Due 

^^2  3  1^ 

'^s. 

-miUM^B 

JM 

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nAi 

nov^6 

[3'***' 

$) 

M651 
Essig 

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dentistry-*, 


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